The lateral twofifths of the clavicle are flattened and have a superior attached. Medially, this surface is related to the lower end of the internal
and an inferior surface, limited by an anterior and a posterior border. jugular vein (from which it is separated by sternohyoid), the termina
The anterior border is concave, thin and roughened, and may be marked tion of the subclavian vein, and the start of the brachiocephalic vein.
by a small deltoid tubercle. The posterior border, also roughened by More laterally, the clavicle arches in front of the trunks and divisions
muscular attachments, is convex backwards. The superior surface is of the brachial plexus and the third part of the subclavian artery. The
roughened near its margins but is smooth centrally, where it can be felt thyrocervical trunk and its branches, the suprascapular and transverse
through the skin. The inferior surface presents two obvious markings. cervical vessels, are immediately behind and above the upper aspect of
Close to the posterior border, at the junction of the lateral fourth with this surface. Subclavius is inserted in the subclavian groove on the
the rest of the bone, a prominent conoid tubercle gives attachment to inferior surface; the clavipectoral fascia is attached to the edges of the
the conoid part of the coracoclavicular ligament. A narrow, roughened groove. The posterior lip of the groove is continuous with the conoid
strip, the trapezoid line, runs forwards and laterally from the lateral side tubercle laterally and brings the clavipectoral fascia into continuity with
of this tubercle, almost as far as the acromial end (see Fig. 48.6B). The the conoid ligament. A nutrient foramen is found in the lateral end of
trapezoid part of the coracoclavicular ligament is attached to it. A small, the groove, running in a lateral direction; the nutrient artery is derived
oval articular facet, for articulation with the medial aspect of the from the suprascapular artery.
acromion, faces laterally and slightly downwards at the lateral end of
Sternal end
the shaft.


Subclavius is attached to the groove on the inferior surface (see Fig. The sternal end of the clavicle is directed medially, downwards and
48.6B). The clavipectoral fascia is attached to the edges of the groove. forwards, and articulates with the clavicular notch of the manubrium
The posterior edge of the groove runs to the conoid tubercle, where sterni. The sternal surface, usually irregular and pitted, is quadrangular
fascia and conoid ligament merge. There is a laterally inclined nutrient (sometimes triangular). Its uppermost part is slightly roughened for
foramen lateral to the groove. Deltoid (anterior) and trapezius (pos attachment of the interclavicular ligament, sternoclavicular capsule and
terior) are attached to the lateral twofifths of the shaft; both muscles articular disc. Elsewhere, the surface is smooth and articular, and it
are directly inserted into the clavicle but are also indirectly inserted into extends on to the inferior surface for a short distance, where it articu
the clavicular periosteum. The coracoclavicular ligaments, attached to lates with the first costal cartilage. The sternal end of the clavicle projects


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upwards beyond the manubrium sterni; it can be felt and seen easily, at around 18–20 years, but this epiphysis is always small and rudimen
forming the lateral wall of the jugular notch, behind which are the tary, and rapidly joins the shaft. Growth is usually complete by 23 years
cricoid cartilage, cricothyroid membrane, the lower part of the thyroid in both sexes.
cartilage of the larynx and the brachiocephalic vein. The sternal ends of
each clavicle thus form a guide to the jugular notch: if the sternal end
of the clavicle is displaced backwards (by traumatic dislocation), the SCAPULA
landmarks of the notch are lost, the trachea is displaced and there will
be difficulty breathing. If the trachea is displaced to one side (for The scapula is a large, triangular bone that lies over the posterolateral
instance, by pneumothorax), the features of the larynx cannot be pal chest wall, covering parts of the second to seventh ribs (see Fig. 46.7),
pated readily. with a vertical long (craniocaudal) axis. It has costal and dorsal surfaces;
superior, lateral and medial borders; inferior, superior and lateral
Ossification
angles; and three processes: the spine, its continuation – the acromion,
The clavicle begins to ossify before any other bone in the body. The and the coracoid process (Figs 48.8, 48.9).
shaft of the bone is ossified in condensed mesenchyme from two The superior and lateral borders and the supraspinous and infra
primary centres, medial and lateral, that appear between the fifth and spinous fossae converge laterally at the lateral angle of the scapula. This
sixth weeks of intrauterine life, and fuse about the fourth–fifth day. region comprises the glenoid fossa, the coracoid process and the neck
Cartilage then develops at both ends of the clavicle. The medial carti of the scapula. Thus, three robust columns of bone converge at the neck
laginous mass contributes more to growth in length than does the region: the lateral border of the spine of the scapula, the coracoid, and


lateral mass; the two centres of ossification meet between the medial the lateral border of the scapula. Load applied through the glenoid fossa
threefifths and lateral twofifths of the clavicle. A secondary centre for or through the coracoid is transmitted into the scapula through these
the sternal end appears in the late teens, or even early twenties, usually columns, which also provide a robust framework for the scapular body.
2 years earlier in females (Fig. 48.7). Fusion is probably rapid but reli The main processes, and thicker parts of the scapula, contain trabecular
able data are lacking. An acromial secondary centre sometimes develops bone for loadbearing; the rest consists of a thin layer of compact bone
for muscular attachments.
Costal surface
Secondary centre
The costal surface, which is directed medially and forwards when the
arm is by the side, is gently concave, especially in its upper part, match
ing the contour of the chest wall (see Fig. 48.8B).
Near the lateral border, there is a longitudinal rounded ridge, promi
nent near the neck but less so below, which is separated from the lateral
Primary centres border by a narrow, grooved area. Subscapularis arises from the sub
Fig. 48.7 The three constant centres of ossification of the clavicle. scapular fossa that comprises nearly the whole of the costal surface,
1 9
11
12 1
10
2
2
3 11
3 4
5
13
4 14
12
5 15
16
17
18 13
6
19
20
6
7
21
8 7
8
9
10
22
A B
23
Fig. 48.8 The left scapula, showing sites of muscular and ligamentous attachment and articular surfaces. A, Posterior aspect. Key: 1, clavicular facet; 2,
biceps brachii (short head); 3, acromion; 4, deltoid; 5, glenoid fossa; 6, triceps brachii (long head); 7 and 9, teres minor; 8, groove for circumflex scapular


artery; 10, teres major; 11, conoid tubercle; 12, coracoid process; 13, omohyoid (inferior belly); 14, superior angle; 15, supraspinatus; 16, levator
scapulae; 17, spine; 18, trapezius; 19, rhomboid minor; 20, infraspinatus; 21, rhomboid major; 22, latissimus dorsi; 23, inferior angle. B, Anterior aspect.
Key: 1, attachment of trapezoid ligament; 2, attachment of conoid ligament; 3, acromion process; 4, suprascapular notch; 5, omohyoid (inferior belly); 6,
serratus anterior; 7, subscapularis; 8, ridge for intermuscular tendon of subscapularis; 9, deltoid; 10, biceps brachii (short head) and coracobrachialis; 11,
pectoralis minor; 12, glenoid fossa; 13, triceps brachii (long head).


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The shaft of the clavicle is usually fractured as a result of a violent
impact to the side of the shoulder. The fracture typically occurs at the
junction of the lateral twofifths and medial threefifths, where the
transition from antecurve to retrocurve occurs. The weight of the arm
causes displacement of the lateral fragment downwards, inwards and
into forward (ventral) rotation. If the fracture heals in this position, the
dimensions and shape of the retroclavicular space are altered, particu
larly during elevation of the arm above shoulder level, and the brachial
plexus (and its perfusion) and the subclavian vessels can be distorted
(one of the many causes of the syndrome associated with thoracic outlet
obstruction).
The clavicle does not ossify exclusively by intramembranous ossifi
cation. In 14 mm embryos, the clavicle is a band of condensed mesen
chyme between the acromion and apex of the first rib, and is continuous
with the sternal rudiment. Medial and lateral zones of early cartilage
transformation (‘precartilage’) occur within this band; intramembra
nous centres of ossification appear, and soon fuse, in the mesenchyme
between them. Sternal and acromial zones become true cartilage into
which ossification extends from the shaft. Length increases by intersti
tial growth of these terminal cartilages; the latter develop zones of
hypertrophy, calcification and advancing endochondral ossification
like other growth cartilages. Diameter increases by subperichondral
deposition in the extremities and subperiosteal deposition in the shaft.
Epiphyses are endochondral and probably fuse in the same way as they
do in long bones. Clavicle growth and development defects include
those of ossification, of morphology (shape) and of length. Defects of
ossification in the clavicle and those cranial bones that ossify by
intramembranous ossification occasionally coincide, e.g. in cleido
cranial dysostosis.
Defects of morphology and length occur in the immature clavicle in
birth lesions of the brachial plexus; the lateral twofifths are affected.


In a typical case, the acromial end of the clavicle is hypercurved, ven
trally rotated by up to 90° and short. The coracoclavicular ligaments
are normal. The coracoid is long and more vertical than usual; the
scapula is often small, and the scapular neck region short with variable
glenoid dysplasia. These characteristic defects are predominantly associ
ated with the upper trunk lesion (C5 and C6) that results in a muscular
imbalance across the acromioclavicular and glenohumeral joints; the
flexor and medial (internal) rotator muscles are relatively short. The
short, tight pectoralis minor and coracobrachialis produce a distorting
force on the coracoid, which elongates and rotates dorsally. With retro
pulsion of the humeral head posteriorly, the scapula rotates ventrally,
particularly if there is posterior glenoid dysplasia. Deltoid shortening
creates a downward distraction on the developing acromion, which
lengthens and curves distally. The spine of scapula is parallel to the
body of the scapula rather than dorsally directed; these deformities
cause the acromioclavicular joint to be orientated more horizontally.
As a result, the lateral clavicle hypercurves ventrally. The concept here
is that dysmorphology is driven by asymmetrical muscle paralysis and
partial recovery, and that form follows the neural lesion. While poor
movement (causing a lack of ‘motivation’ for growth in length) might
explain the clavicular shortening, an equally valid explanation might
involve a vascular insufficiency of the lateral ossification centre of the
clavicle (with a similar insufficiency of the lateral ossification centres of
the scapula for the glenoid): both have a contribution from the supra
scapular artery, which is ‘at risk’ during injuries that lead to brachial
plexus palsy. Length is a function of perfusion and shortening follows
vascular insufficiency (Kambhampati et al 2006).


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5
6
1
7 6
8 1
2 7
2
9
3
10
4
3
5
4
8
A B 9
Fig. 48.9 The left scapula, showing sites of muscular and ligamentous attachment and articular surfaces. A, Superior aspect. Key: 1, facet for clavicle;
2, acromial process; 3, spine; 4, superior border; 5, head; 6, glenoid fossa; 7, neck; 8, conoid tubercle (for conoid ligament); 9, coracoid process; 10,
attachment of trapezoid ligament. B, Lateral aspect. Key: 1, coracoid process; 2, supraglenoid tubercle; 3, glenoid fossa; 4, infraglenoid tubercle for long
head of triceps brachii; 5, ventral surface; 6, acromion; 7, acromial angle; 8, lateral border; 9, inferior angle.
including the grooved area immediately adjoining the lateral border, the infraspinous fossa. The lower limit of the attachment of teres minor
but excluding the area next to the neck of the bone. Small, fibrous is indicated by an oblique ridge, which runs from the lateral border to
intramuscular septa are attached to four or five roughened ridges that the neighbourhood of the inferior angle and cuts off a somewhat oval
subdivide this surface incompletely into a number of smooth areas. The area where teres major is attached. The dorsal aspect of the inferior
anterior aspect of the neck is separated from subscapularis by a bursal angle may give origin to a small slip that joins the deep surface of latis
protrusion of the synovial membrane of the shoulder joint (subscapular simus dorsi. The infraspinous fossa is hollowed out laterally but is
‘bursa’). The lower five or six digitations of serratus anterior are attached convex medially. Infraspinatus is attached to the infraspinous fossa,


to an oval area near the inferior angle. The remainder of the muscle is with the exception of an area near the neck of the bone. The strong
inserted into a narrow strip along the ventral aspect of the medial infraspinatus fascia passes on to teres minor and teres major, and sends
border, which is wider above, where it receives the large first digitation. fascial partitions between them that reach the bone along the ridges
The longitudinal thickening of the bone near the lateral border provides marking the limits of their attachments.
a column of the necessary strength to withstand the pull of serratus
anterior on the inferior angle during lateral scapular rotation, when the Superior border
glenoid cavity is turned to face more directly upwards as the arm is The superior border, thin and sharp, is the shortest. At its anterolateral
raised from the side and carried above the head against gravity. end, it is separated from the root of the coracoid process by the supra
scapular notch (see Fig. 48.8B), which can vary in shape and size.
Dorsal surface Medial to the suprascapular notch, the superior border gives origin to
The dorsal surface is divided by the transverse, shelflike spine of the the inferior belly of omohyoid. The notch is bridged by the superior
scapula into two unequal parts: a smaller supraspinous fossa above and transverse ligament (or suprascapular ligament), which is attached lat
an infraspinous fossa below. The fossae are confluent at the spino erally to the root of the coracoid process and medially to the limit of
glenoid notch between the lateral border of the spine and the dorsal the notch. The ligament is sometimes ossified. The foramen, thus com
aspect of the neck; their central parts may be very thin (see Fig. 48.8A). pleted, transmits the suprascapular nerve to the supraspinous fossa,
The supraspinous fossa is bounded superiorly and anteriorly by the whereas the suprascapular vessels pass backwards above the ligament.
superior border, from the suprascapular notch and dorsal aspect of the
Lateral border
root of the coracoid laterally, to the superior angle medially; and medi


ally, by the upper part of the medial border. The infraspinous fossa is The lateral border has a triangular or rhomboidal crosssection. It forms
bounded by the medial and lateral borders and the inferior angle. a clearly defined, sharp, roughened ridge that runs sinuously from the
Supraspinatus is attached to the medial twothirds of the supra inferior angle to the glenoid cavity. At its upper end, it widens into a
spinous fossa on the dorsal surface; the fascia that covers the muscle is rough, somewhat triangular, area: the infraglenoid tubercle (see Fig.
attached to the margins of the fossa. A fat pad lies between the supra 48.9B). The lateral border separates the attachments of subscapularis
spinatus fascia and the undersurface of trapezius. Teres minor is and teres minor and major. These muscles project beyond the bone and,
attached to the upper twothirds of a flattened strip that adjoins the with latissimus dorsi below, cover it so completely that it cannot be felt
lateral border. The strip is grooved near its upper end by the circumflex through the skin. The long head of triceps is attached to the infraglenoid
scapular vessels passing between teres minor and the bone as they enter tubercle.


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The grooved part of the costal surface, the narrow, flat lateral strip border of the crest and, to a variable extent, to the medial border by
of the dorsal surface and the adjacent thickened ridge (see Fig. 48.9B) attachment to the infraspinatus fascia. The middle fibres of trapezius
are often included in the ‘lateral column’ in surgical practice. By defini are attached to the upper border of the crest. The lowest fibres of tra
tion, the remainder of the scapular body (costal and dorsal surfaces) pezius terminate in a flat, triangular tendon that glides over the smooth
and the medial border are called the ‘medial column’. area at the base of the spine and inserts into a rough prominence,
erroneously called the deltoid tubercle, on the dorsal or subcutaneous
Medial border
aspect of the spine near its medial end.
The medial border extends from the inferior to the superior angle. It is
Acromion
slightly thickened and flat, and is further thickened at the medial end
of the spine. In its lower twothirds, this border can easily be felt The acromion projects forwards, almost at right angles, from the lateral
through the skin, but its upper third is more deeply placed and more end of the spine, with which it is continuous. The lower border of the
difficult to palpate. It is thin and often angled opposite the root of the crest of the spine becomes continuous with the lateral border of the
spine. Levator scapulae is attached to a narrow strip, extending from the acromion at the acromial angle, which forms a reliable, subcutaneous,
superior angle to the root of the spine, and rhomboid minor is attached bony landmark. The medial border of the acromion is short and is
below this, opposite the root of the spine. Rhomboid major is attached marked anteriorly by a small, oval facet, directed upwards and medially,
to the remainder of the border. for articulation with the lateral end of the clavicle. The lateral border,
tip and upper surface of the acromion can all be felt through the skin
Scapular angles without difficulty. There may be an accessory articular facet on the


The inferior angle lies over the seventh rib, or over the seventh inter inferior surface of the acromion.
costal space. It can be felt through the skin and the muscles that cover The acromion is subcutaneous over its dorsal surface, being covered
it, and, when the arm is raised above the head, it can be seen to rotate only by the skin and superficial fascia. The lateral border, which is thick
forwards (protract) around the chest wall; when the arm is lowered, the and irregular, and the tip of the process, as far round as the clavicular
scapula should restitute (retract) to its original position without a dis facet, give origin to the middle fibres of deltoid. The medial aspect of
turbance of rhythm. It is covered on its dorsal aspect by the upper the tip gives attachment, below deltoid, to the lateral end of the coraco
border of latissimus dorsi, a small slip from which is frequently attached acromial ligament. The articular capsule of the acromioclavicular joint
to the inferior angle. The superior angle, at the junction of the superior is attached around the margins of the clavicular facet. Behind the facet,
and medial borders, is obscured by the upper part of trapezius. It lies the medial border of the acromion gives insertion to the horizontal
over the dorsal surface of the second rib and can be palpated deeply (middle) fibres of trapezius. The inferior aspect of the acromion is rela
above and behind the clavicle. tively smooth and forms a protective arch over the shoulder joint,
The lateral angle, truncated and broad, comprises the glenoid fossa together with the coracoacromial ligament and the coracoid process.
(cavity) and scapular neck, with the coracoid projecting forwards. When The tendon of supraspinatus passes below the overhanging acromion
the arm is by the side, the fossa is directed forwards, laterally and and is separated from it and from deltoid by the subacromial bursa.
slightly upwards. When the arm is raised above the head, it is directed
Coracoid process
almost straight upwards, i.e. the plane of the fossa is horizontal. The


supraglenoid tubercle is a small, rough, sloping area at the cranial The coracoid process arises from the upper border of the neck of the
margin of the fossa; it often encroaches on the root of the coracoid scapula and its body is bent sharply so as to project forwards and
process, and is the site of attachment for the tendon of the long head slightly laterally (see Figs 48.8, 48.9). When the arm is by the side, the
of biceps brachii. The infraglenoid tubercle is a larger, rough area at the coracoid process points almost straight forwards. Its tip can be felt
caudal margin of the glenoid fossa, at the upper end of the lateral through the skin and is covered by the anterior fibres of deltoid, about
margin, and is the site of attachment for the tendon of the long head 2.5 cm below the clavicle at the junction of the lateral fifth with the rest
of the triceps brachii. The anatomical neck is the region of the scapula of the bone, at the lateral border of the infraclavicular fossa. It forms a
extending between the infraglenoid and supraglenoid tubercles anteri short, curved cantilever fixed to the scapula at its base and is displaced
orly and posteriorly, lateral to the root of the coracoid process; anteri by the actions of the muscles attached to its body and tip. Pectoralis
orly, there is no landmark to distinguish the anatomical neck from the minor pulls the coracoid (and, therefore, the scapula) forwards and
costal surface of the body of the scapula. Posteriorly, the anatomical medially around the chest wall, balanced by trapezius, its antagonist;
neck is limited by the spinoglenoid notch at the root of the spine of this action forms the foundation on which coracobrachialis can help
the scapula. The bone here has an asymmetric, triangular crosssectional support the long lever arm of the humerus during humeral motion,
shape; the plane of the anterior surface of the neck makes an acute angle together with its antagonist, the deltoid.


of about 60° with the plane of the glenoid fossa, but the dimension The infraclavicular brachial plexus and the axillary vessels lie below
and shape of the posterior surface are more variable. and medial to the coracoid. The acromial branch of the thoraco
acromial artery passes above it, and the sensory branch of the lateral
Spine of the scapula pectoral nerve to the rotator interval capsule, together with accompany
The spine of the scapula forms a shelflike projection on the upper part ing vessels, lies immediately below.
of the dorsal surface of the bone, and is triangular in shape (see Fig. On the dorsal aspect of the coracoid process, at the point where it
48.8A). Its lateral border is free, thick and rounded, and bounds the changes direction, a rough impression forms part of the region of
spinoglenoid notch, which lies between it and the dorsal surface attachment of the conoid portion of the coracoclavicular ligament. The
of the neck of the bone. Its anterior aspect joins the dorsal surface of trapezoid portion of the coracoclavicular ligament is attached to the
the scapula along a line that runs laterally and slightly upwards from upper aspect of the horizontal part of the process, anterior to the conoid
the junction of the upper and middle thirds of the medial border. The part. Pectoralis minor is attached to the superior and medial aspects of
platelike body of the bone is bent along this line, which accounts for the coracoid process. The wider, medial, end of the coracoacromial
the concavity of the upper part of the costal surface. The dorsal border ligament is attached to the lateral border and is continuous inferiorly
is the crest of the spine and is subcutaneous throughout nearly its whole with the lateral aponeurotic part of the tendon of the short head of
extent. The crest expands into a smooth, triangular area at its medial biceps brachii. The coracohumeral ligament is attached to the root of
end. Elsewhere, the upper and lower edges and the surface of the crest the coracoid at its lateral border. The interval between the anterior
are roughened for muscular attachments. The upper surface of the spine aspect of the scapular neck immediately medial to the glenoid fossa


widens as it is traced laterally and is slightly hollowed out. Together and the deep surface of the coracoid is often bridged by the glenocora
with the upper area of the dorsal surface of the bone, the upper surface coid ligament. The inferior aspect of the coracoid process is otherwise
of the spine forms the supraspinous fossa. The lower surface is overhung smooth and saddleshaped. When the arm is elevated, the upper border
by the crest at its medial, narrow end, but is gently convex in its wider, of subscapularis is apposed to, and runs under, this surface, which
lateral portion. Together with the lower area of the dorsal surface of the forms a pulley for the muscle, increasing the power generated during
bone, the lower surface of the spine forms the infraspinous fossa, which forceful medial (internal) rotation of the shoulder in elevation, such as
communicates with the supraspinous fossa through the spinoglenoid during a serve in tennis. Coracobrachialis is attached to the deep aspect
notch. of the lower part of the medial side and the deep surface of the tip of
Supraspinatus is attached to the upper surface of the spine of the the process, and the short head of biceps is attached to the lateral side
scapula; the infraspinatus, by contrast, is not attached to the lower and superficial aspect of the tip.
surface of the spine. The flattened triangular area at its root lies opposite
Scapular movements
the spine of the third thoracic vertebra and is covered by the tendon of
trapezius; a bursa intervenes to enable the tendon to play over this part Scapular movement is a product of interconnected suspension, motion
of the bone. The posterior fibres of deltoid are attached to the lower and articulation mechanisms. The suspension mechanism consists of


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the scapular articulation with the clavicle and the suspension muscles A
of the scapula and clavicle, notably trapezius, attached to the lateral Distal acromial centre
clavicle, the acromion and the spine of scapula. The articulation with
Proximal acromial centre
the clavicle comprises two linked systems: ‘clavicle – acromioclavicular
Coracoid centre
joint – acromion – spine of scapula – lateral scapular angle’ and ‘clavicle
– coracoclavicular ligament – coracoid – lateral scapular angle – spine
of scapula’. This mechanism therefore subserves the function of scapular
rotation or tilt limited by the ellipsoid range of motion of the lateral
clavicle. The motion mechanism consists of the agonist–antagonist
force couple of serratus anterior passing to the chest wall anterolaterally,
and levator scapulae, rhomboid major, rhomboid minor and serratus
posterior (when present), which all pass to the vertebral column medi
ally. This mechanism therefore subserves the function of scapular pro Centre for medial border
traction and retraction around the elliptic paraboloid of the chest wall.
The articulation mechanism consists of the scapular neck region and
the glenoid fossa, which articulates with the humeral head. The muscles
that subserve the function of holding the humeral head on the glenoid
through the wide range of motion of the glenohumeral joint are the
rotator cuff muscles, which take their attachment from the body of the
scapula. This mechanism therefore concerns the relationship between
the position and orientation of the glenoid fossa and the scapular body.
Ossification
The cartilaginous scapula is ossified from eight or more centres: one in
the body, two each in the coracoid process and the acromion, and one
each in the medial border, inferior angle and lower part of the rim of
the glenoid cavity (Fig. 48.10). The centre for the body appears in the
Centre at inferior angle
eighth intrauterine week. Ossification begins in the middle of the cora
B
coid process in the first year or, in a small proportion of individuals,


before birth; the process joins the rest of the bone about the fifteenth
Subcoracoid centre
year. At or soon after puberty, centres of ossification occur in the rest of Distal acromial centre
the coracoid process (subcoracoid centre), in the rim of the lower part
of the glenoid cavity, frequently at the tip of the coracoid process, in
the acromion, in the inferior angle and contiguous part of the medial
border and in the medial border. A variable area of the upper part of
the glenoid cavity, usually the upper third, is ossified from the subcora
coid centre; it unites with the rest of the bone in the fourteenth year in Glenoid centre
the female and the seventeenth year in the male. A horseshoeshaped
epiphysis appears for the rim of the lower part of the glenoid cavity;
thicker at its peripheral than at its central margin, it converts the flat
glenoid cavity of the child into the gently concave fossa of the adult.
The base of the acromion is formed by an extension from the spine;
the rest of the acromion is ossified from two centres that unite and then
join the extension from the spine. The various epiphyses of the scapula
have all joined the bone by about the twentieth year.
The normal fetal scapula differentiates in somitic ectoderm at about
5 weeks in utero juxtaposed to the fourth, fifth and sixth cervical verte
bral anlagen. As the neural axis and cardiac primordia develop between
the ninth and twelfth weeks, the primordial scapula migrates caudally
to its usual position at a level between the second and seventh ribs.
With further development, the scapula alters shape.
Ligaments Fig. 48.10 Ossification of the scapula. A, Dorsal aspect. B, Lateral
The intrinsic scapular ligaments are strengthening ligaments (coraco aspect. (Adapted from Drake RL, Vogl AW, Mitchell A (eds), Gray’s
acromial ligament) and bounding ligaments (superior transverse Anatomy for Students, 2nd ed, Elsevier, Churchill Livingstone. Copyright
scapular or suprascapular ligament, inferior transverse scapular or 2010.)
spinoglenoid ligament, and the variable glenocoracoid ligament).


Coraco-acromial ligament The coracoacromial ligament is a strong
triangular band between the coracoid process and acromion. It is notch into a foramen; it is sometimes ossified. A flat fasciculus, it
attached apically to the acromion anterior to its clavicular articular narrows towards its attachments to the base of the coracoid process,
surface, and by its base along the whole lateral border of the coracoid. blending with the lower fibres of the conoid ligament, and to the
Together with the coracoid process and acromion, it completes an arch medial side of the scapular notch. The suprascapular nerve traverses the
above the humeral head. It may be composed of two strong marginal foramen, and the suprascapular vessels cross above the ligament.
bands with a thinner centre; when pectoralis minor is inserted into the
humeral capsule instead of the coracoid process, which happens occa Inferior transverse scapular (spinoglenoid) ligament When present,
sionally, its tendon passes between the bands. The subacromial bursa the inferior transverse scapular ligament is a membranous ligament
facilitates movement between the coracoacromial arch and the sub that may stretch from the lateral border of the spine of the scapula to
jacent supraspinatus and shoulder joint, functioning as a secondary the glenoid margin (see Fig. 48.33). It forms an arch over the branches
synovial articulation. When the coracoacromial ligament is cut, it is of the suprascapular nerve and vessels entering the infraspinous fossa
impossible to appose the two cut surfaces afterwards: this suggests there to supply infraspinatus.
is resting tension in the ligament, which forms a ‘tension band’ between
the acromial and coracoid processes of the scapula, so ‘pretensioning’
both processes against the distracting forces of deltoid and trapezius, HUMERUS
and pectoralis minor and the conjoined short head of biceps brachii
and coracobrachialis, respectively. The humerus, the longest and largest bone in the upper limb, has
expanded ends and a shaft (Figs 48.11–48.12). The spheroidal humeral


Superior transverse scapular (suprascapular) ligament The superior head forms an enarthrodial articulation with the glenoid fossa of the
transverse scapular (suprascapular) ligament converts the scapular scapula. The lesser tubercle projects from the front of the shaft, close


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Initially, the horizontal diameter exceeds the vertical but the ratio
gradually decreases until mature dimensions are reached, an adaptation
thought to provide upright hominids with increased range, and there
fore freedom of use, of the upper limb. Avian genedeletion studies have
shed light on the development of the scapula. Scapular body develop
ment appears to be controlled by the Emx2 gene, also expressed in the
developing mesonephros. The development of the acromion and the
spine of the scapula are controlled by the Pax1 gene, and glenoid and
coracoid development is controlled by the Hoxc6 gene (Huang et al
2000), one of the homeobox genes responsible for somite differentia
tion and development; development of the glenoid and coracoid
appears likely to be more intimately related to the development of the
upper limb bud as a whole. The development of the scapular body
appears to be independent of that of the processes and glenoid region.
Adult scapulae may show a line of fusion across the body and spine of
the scapula, suggesting that the primordia of the processes (including
the glenoid) and the primordium of the body migrate towards each
other; since the trapezius is derived from branchial arch mesoderm it
would appear that the development of the spine of the scapula and
acromion and trapezius are intimately related, but separate from the
body. This hypothesis is supported by the observation that; in the con
dition of socalled Sprengel shoulder (more correctly termed congenital
undescended scapular syndrome), the development of the scapular
body is altered, and there is intramuscular ossification of variable parts
of the medial scapulospinal muscles, but the development of the pro
cesses (including the glenoid) is unaffected (Dhir and Lambert 2014).
The suprascapular nerve may be entrapped by the ligament if this is
thickened or ossified and this may cause the syndrome of neurostenal
gia, a typical pain of unremitting burning or aching nature, due to
stenosis or distortion of the nerve trunk by extrinsic compression.
Weakness of supraspinatus and infraspinatus may subsequently occur.


Surgical release of the ligament is often helpful; this may be undertaken
by open or arthroscopic surgical exposure and division of the ligament.
A ganglion (an outpouching of the synovial membrane of the gleno
humeral joint) may occur immediately behind and above the postero
superior corner of the glenoid fossa; this can compress the branch of
the suprascapular nerve that supplies infraspinatus as it courses around
the lateral aspect of the spine of the scapula under the inferior scapular
ligament. Since the nerve cannot move aside (it is ‘held’ under the liga
ment), it can be readily distorted; there is characteristic severe pain,
followed by specific atrophy of infraspinatus. Decompression of the
ganglion and division of the ligament are curative in the early stage of
this syndrome. An intraneural ganglion may arise from the articular
branch of the suprascapular nerve; muscular pain and atrophy would
be expected to be more rapid than in the case of the synovial ganglion
(Spinner et al 2006).


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Fig. 48.11 The left humerus showing sites of
6 muscular attachments. A, Anterior aspect. Key: 1,
1 subscapularis; 2, triceps brachii (medial head); 3,
coracobrachialis; 4, pronator teres (humeral head);
1 5, common flexor origin; 6, supraspinatus; 7,
2
pectoralis major; 8, latissimus dorsi; 9, teres
major; 10, deltoid; 11, brachialis; 12,
brachioradialis; 13, extensor carpi radialis longus;
14, common extensor origin. B, Posterior aspect.
Key: 1, infraspinatus; 2, teres minor; 3, triceps
brachii (lateral head); 4, deltoid; 5, brachialis; 6,
7
3 triceps brachii (medial head); 7, anconeus.
8
9
4
2
3 10
5
11
6
12
13
4
14
5
A B
7
Fig. 48.12 The proximal end of the left humerus.
A, Anterior aspect. Key: 1, head; 2, anatomical
neck; 3, surgical neck; 4, greater tubercle; 5,
1 4 1 5 l Be ,s s Pe or s t tu eb rie or rc ale s; p 6 e, c i tn . t Ke ert yu :b 1e ,r c gu rela ar t es ru l tc uu bs e; r c7 l, e s ; h 2a , ft.
surgical neck; 3, shaft; 4, radial groove; 5, head;
5 6 6, anatomical neck.
2
6
2
3
3
7
4
A B


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to the head, and is limited on its lateral side by the wellmarked groove, upper part of this area and separate it from deltoid. The intertubercular
the intertubercular sulcus, by which it is separated from the greater sulcus (bicipital groove) lies between the tubercles. It contains the long
tubercle. The distal end is adapted to the forearm bones at the elbow tendon of biceps, its synovial sheath, and an ascending branch from
joint and carries the medial and lateral epicondyles with the articular the anterior circumflex humeral artery. The rough lateral lip of the
surfaces for the radius and ulna between them. The axis between the groove is marked by the bilaminar tendon of pectoralis major, and its
epicondyles is the interepicondylar axis. medial lip by the tendon and muscular insertion of teres major. The
The shaft of the human (and primate) humerus is relatively medially floor of the groove provides attachment for a frequent upward extension
rotated with respect to the humeral head, compared with quadripedal of the tendon of pectoralis major, and for the tendon of latissimus dorsi
ancestors; this gives the characteristically greater range of external rota more caudally (Dancker 2013).
tion at the glenohumeral joint than that obtaining in other species. This
is reflected in the spiroidal architecture of the adult humeral medullary Shaft
cavity, the arrangement and relationship of the posterior compartment
of brachial muscles and the radial nerve, and the disposition to long
The shaft of the humerus is almost cylindrical in its proximal half.
spiroidal fractures caused by external twisting forces.
Distal to the deltoid tuberosity, it is equilaterally triangular in cross
With the arm by the side in the anatomical position, and with the
section, flaring out into a broad isosceles triangular crosssection just
medial and lateral epicondyles in the same (frontal) plane (i.e. the
above the elbow joint. It can be readily palpated laterally and medially,
interepicondylar axis is in the frontal plane), the humeral head is


but the muscles of the anterior and posterior compartments obscure
rotated posteriorly at an angle averaging 15–20° in European cadaveric
the bone to palpation anteriorly and posteriorly. It has three surfaces
specimens (Boileau and Walch 1997). Since the glenoid fossa of the
and three borders, which are only distinct towards the elbow joint. The
scapula faces anterolaterally, the humerus is not rotated posteriorly
shaft comprises the middle threefifths of the humerus.
relative to the scapula in the anatomical position. It is important to
remember this position of the bone when movements of the arm and Surfaces
forearm are considered; movements are recorded relative to the trunk The posterior surface, between the medial and lateral borders, is broad,
(starting in the anatomical position) or relative to the scapula, and it flat and convex distally. The medial head of triceps is attached to the
is important to define which method is in use. posterior surface over an elongated triangular area, the apex of which
is placed on the medial part of the bone above the level of the lower
Proximal end limit of insertion of teres major. The area widens below and covers the
whole surface almost down to the lower end of the bone. The lateral
head of triceps is attached to a ridge, sometimes rough, that descends
The proximal end of the humerus consists of the head, anatomical neck,
obliquely and laterally above the attachment for the medial head.
and the greater and lesser tubercles. It joins the shaft at an illdefined
Above triceps, the axillary nerve and the posterior circumflex humeral
‘surgical neck’, which is closely related on its medial side to the axillary
vessels wind around the bone on the deep surface of deltoid. Below the
nerve and posterior humeral circumflex artery (see Figs 48.22, 48.31,
attachment of the lateral head of triceps, but above the attachment of
48.33). The proximal end of the humerus makes up the upper fifth of
the medial head, a shallow groove runs from the upper medial aspect
the length of the bone.
of the surface downwards and laterally towards the lateral border; it
contains the radial nerve and its branches, and the profunda brachii
Head
vessels.


The head of the humerus forms rather less than half a spheroid; in
The anterolateral surface is bounded by the anterior and lateral
sectional profile, it is spheroidal (strictly, ovoidal) (see Fig. 48.12). Its
borders, and is smooth and featureless in its upper part, which is
smooth articular surface is covered with hyaline cartilage that is thicker
covered by deltoid. About, or a little above, the middle of this surface,
centrally. When the arm is at rest by the side, it is directed medially,
deltoid is attached to the deltoid tubercle. Further distally, the surface
backwards and upwards to articulate with the glenoid cavity of the
gives origin to the lateral fibres of brachialis, which extend upwards into
scapula. The humeral articular surface is much more extensive than the the floor of the lower end of the groove for the radial nerve (see Fig.
glenoid cavity, which means that only a portion of it is in contact with
48.11). The nerve perforates the lateral intermuscular septum close to
the cavity in any one position of the arm.
the bone at the level of the junction of the upper threefifths and lower
twofifths of the humerus, and enters the anterior compartment of the
Anatomical neck
arm close to the anterolateral surface, between brachialis medially and
The anatomical neck of the humerus immediately adjoins the margin brachioradialis laterally.
of the head, forming a slight constriction that is least obvious next to The anteromedial surface is bounded by the anterior and medial
the greater tubercle. A slight roughness indicates the line of capsular borders. Below the intertubercular sulcus, the rest of the upper half of
attachment of the shoulder joint, other than at the intertubercular the surface is smooth and devoid of muscular attachment; its lower
sulcus, where the long tendon of biceps brachii emerges. Medially, the half is occupied by the medial part of brachialis (see Fig. 48.11A).
capsular attachment diverges from the anatomical neck and descends Coracobrachialis is attached to a long rough strip in the middle third


1 cm or more on to the shaft. of the medial border, posterior to the brachial neurovascular sheath,
which lies in close relation to the humerus in the middle third of this
Lesser tubercle
surface. The humeral head of pronator teres is attached to a narrow
The lesser tubercle is anterior to and just distal to the anatomical neck. area close to the lowest part of the medial supracondylar ridge; the
It is palpable through the thickness of deltoid about 3 cm below the ridge itself gives attachment to the medial intermuscular septum of
anterior edge of the acromion. It can be distinguished from the coracoid the arm.
by rotation of the humerus under the palpating finger; the lesser tuber A little below its midpoint, the nutrient foramen, which is directed
cle slips away from the examining finger, the tip of the coracoid does downwards, opens close to the medial border. A hookshaped process
not. The lateral edge of the lesser tubercle is sharp and forms the medial of bone, the supracondylar process, ranging from 2 to 20 mm in length,
border of the intertubercular sulcus. Subscapularis is attached to the occasionally projects from the anteromedial surface of the shaft,
lesser tubercle (see Fig. 48.11A). The transverse ligament of the shoulder approximately 5 cm proximal to the medial epicondyle. It is curved
(transverse humeral ligament) is attached to the upper aspect of the downwards and forwards, and its pointed apex is connected to the
lateral margin of the tubercle. medial border, just above the epicondyle, by a fibrous band, to which
part of pronator teres is attached. The foramen completed by this
Greater tubercle
fibrous band usually transmits the median nerve and brachial artery,
The greater tubercle is the most lateral part of the proximal end of the but sometimes encloses only the nerve, or the nerve plus the ulnar artery
humerus and projects beyond the lateral border of the acromion. Its (in cases of high division of the brachial artery). A groove that lodges
posterosuperior aspect, near the anatomical neck, bears three smooth, the artery and nerve usually exists behind the process.


flattened impressions for the attachment of supraspinatus (uppermost),
Anterior border
infraspinatus (middle) and teres minor (lowest and placed on the pos
terior surface of the tubercle) (see Fig. 48.11). The attachments of sub The anterior border starts on the front of the greater tubercle and runs
scapularis and teres minor are not confined to their respective tubercles, downwards almost to the lower end of the bone. Its proximal third
but extend for varying distances on to the adjacent metaphysis. The forms the lateral lip of the intertubercular sulcus and is roughened for
projecting lateral surface of the tubercle presents numerous vascular muscular attachments. The succeeding portion is also roughened and
foraminae and is covered by deltoid, producing the normal rounded forms the anterior limit of the deltoid tubercle; the lower half of the
contour of the shoulder. A part of the subacromial bursa may cover the border is smooth and rounded.


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Lateral border Fractures of the humeral shaft
The lateral border is most conspicuous at the lower end of the bone, Humeral shaft fractures are common; the pattern of the fracture and
where it is thickened to form the lateral supracondylar ridge, and its the displacement of the fragments depend on the force of injury and
sharp edge is roughened along its anterior aspect. In its middle and on the level at which the bone is broken. If there is wide displacement
upper thirds, the border is barely discernible, but in a wellmarked bone at the time of fracture, closely associated nerves and vessels are at risk
it can be traced upwards to the posterior surface of the greater tubercle. of direct injury. Nerves that are ‘fixed’ in relation to the bone and
A little above its middle, it is marked by a Vshaped, roughened area: attached septa are at further risk of indirect injury by stretching or, later,
the deltoid tubercle. The limbs of the V are broad; the groove for the by the callus of bone healing. (For a discussion of radial nerve injury
radial nerve runs downwards and laterally behind the posterior limb and fractures of the humeral shaft, see Lambert (2005).)
and fades away on the lower part of the anterolateral surface. The
lateral intermuscular septum is attached to the lateral border, and is a Distal end
condensation of the fascia over the lower part of deltoid and the neigh
bouring brachialis, forming a septum between the anterior and poste
The distal end of the humerus is described in on page 838.
rior muscular compartments. The septum is most obvious in the lower
threefifths of the arm, and is perforated by the radial nerve and accom
Ossification
panying vessels.
Medial border
The proximal humerus and shaft are ossified from four centres: one
The medial border, although rounded, can be identified without diffi each in the shaft, head, greater and lesser tubercles (Fig. 48.13). The
culty in the lower half of the shaft, where it becomes the medial supra centre for the shaft appears near its middle in the eighth week of intrau


condylar ridge. In its proximal third, the medial border is indistinct terine life, and gradually extends towards the ends. Most growth occurs
until it broadens out to form a triangular area. The lateral border of at the distal end of the bone. Ossification begins in the head before
this area forms the medial lip of the intertubercular sulcus, and the birth (20%) or in the first 6 months afterwards; the greater tubercle
medial border runs upwards as the calcar humerale to the anatomical starts to ossify during the first year in females and second year in males;
neck, where it is roughened, with vascular apertures, and forms the area the lesser tubercle begins to ossify at about the fifth year.
of attachment of the inferior part of the shoulder capsule. In its middle By the sixth year, the centres for the head and tubercles have joined
third, the medial border is interrupted by a wide, shallow groove, the to form a single large epiphysis, hollowed out on its inferior surface to
radial (spiral) groove that crosses the bone obliquely, passing down adapt to the conical upper end of the metaphysis. This macroscopic
wards and forwards from its posterior to its anterior surface. topography provides for mechanical stability in the physis during
A Fuse at sixth year
Six months Eighteen months Second year Fifth year Ninth to tenth year Twelth year
al
Fet
Unites with shaft
at twentieth year
Blend at puberty and unite with
shaft at fourteen to sixteen years
B Joins shaft at C Joins shaft at
fourteenth fourteenth
to seventeenth to sixteenth
year year
h h
birt
At first year At fourth to fifth year At eighteenth year
birt
At At
Fifth to sixth year Ninth to eleventh year Sixteenth year
Joins shaft at
Joins shaft at seventeenth to
seventeenth to
eighteenth year
nineteenth year
Fig. 48.13 The stages in ossification of (A) the humerus, (B) the radius and (C) the ulna (not to scale).


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Articular disc Fibrocartilages Anterior sternoclavicular ligament
Interclavicular ligament
Costoclavicular ligament,
posterior fibres Costoclavicular ligament
First costal cartilage
Second costal cartilage
Second sternocostal joint;
double synovial; fibrocartilages;
Manubriosternal symphysis intra-articular ligament
Fig. 48.14 The sternoclavicular joints, anterior aspect. The joint on the left side is intact and the joint on the right side is shown in coronal section.
growth, although rotational stability is still relatively poor; adolescent sternal ends of both clavicles; some fibres are attached to the superior
proximal humeral physial fractureseparations are commonly unstable manubrial margin.
in rotation. The proximal humeral epiphysis fuses with the shaft of the
humerus at about the thirteenth or fourteenth year in females, begin Costoclavicular ligament The costoclavicular ligament is like an
ning on the medial aspect of the physial line, and between the four inverted cone, but short and flattened. It has anterior and posterior
teenth to sixteenth year in males. laminae that are attached to the upper surface of the first rib and costal
cartilage, and ascends to the margins of an impression on the inferior
clavicular surface at its medial end. Fibres of the anterior lamina ascend
JOINTS laterally and those of the posterior lamina (which are shorter) ascend
medially (see Fig. 48.14). They fuse laterally and are closely related to
the attachments of subclavius, particularly the tendon of origin; it can
STERNOCLAVICULAR JOINT
be hard to distinguish the lateral border of the ligament from the
tendon. The ligament merges medially with the capsule. It can be ossi
The sternoclavicular joint is a synovial sellar (saddle, or hyperbolic
fied in older adults, particularly females. A few deep fibres of pectoralis
paraboloid) joint with an intraarticular fibrocartilaginous disc. It is the
major attach to the external surface of the ligament, adjacent first rib,
only skeletal articulation between the upper limb and the axial skeleton


first costal cartilage and manubrium sterni.
(Sewell et al 2013).
Articular disc The fibrocartilaginous articular disc divides the cavity
Articulating surfaces The articulating surfaces are the sternal end
of the joint into two compartments between the sternal and clavicular
of the clavicle and the clavicular notch of the sternum, together with
surfaces. It is attached above to the posterosuperior border of the articu
the adjacent superior surface of the first costal cartilage (Fig. 48.14).
lar surface of the clavicle, below to the first costal cartilage near its
The larger clavicular articular surface is covered by fibrocartilage, which
sternal junction, and by the rest of its circumference to the capsule, and
is thicker than the fibrocartilaginous lamina on the sternum. The joint
therefore adapts to the contour of the clavicular surface. It is thicker
is convex vertically but slightly concave anteroposteriorly, and is there
peripherally, especially superoposteriorly and inferomedially; the
fore sellar; the clavicular notch of the sternum is reciprocally curved but
central part of the disc may be perforated in later life.
the two surfaces are not fully congruent. An articular disc completely
divides the joint. Vascular supply The sternoclavicular joint is supplied by branches
from the internal thoracic and suprascapular arteries.
Fibrous capsule The capsule is thickened anteriorly and posteriorly,
but superiorly and especially inferiorly, it is little more than loose Innervation The sternoclavicular joint is innervated superficially by
areolar tissue. branches from the medial supraclavicular nerve and deeply by the nerve
to subclavius.
Ligaments There are two sets of associated ligaments. The intrinsic
ligaments are the anterior and posterior sternoclavicular ligaments; the Factors maintaining stability There is almost no bony articular
extrinsic ligaments are the midline interclavicular ligament and the congruence at the sternoclavicular joint. However, the strength of its
costoclavicular ligaments on each side. associated ligaments and the articular disc produce durable stability.
These factors make sternoclavicular joint dislocation rare; fracture of


Anterior sternoclavicular ligament The anterior sternoclavicular liga the clavicular shaft is far more common for the same force directed
ment is broad and attached above to the anterosuperior aspect of the along the clavicle. (See Sewell et al (2013)) for a review of the mecha
sternal end of the clavicle. It passes inferomedially to the upper anterior nisms and treatment of sternoclavicular instability.)
aspect of the manubrium, spreading on to the first costal cartilage.
Movements The capsule around the clavicular attachment is more
Posterior sternoclavicular ligament The posterior sternoclavicular lax. Movements between the clavicle and the disc are more extensive
ligament is a weaker band posterior to the joint. It descends inferomedi than those between the disc and sternum. The sellar shape of the articu
ally from the posterior aspect of the sternal end of the clavicle to the lar surfaces permits translation or gliding in approximately anteropos
posterior aspect of the upper manubrium. terior and vertical planes, with rotation about the long axis of the
clavicle. Closepacking coincides with maximum posterior rotation
Interclavicular ligament The interclavicular ligament is continuous associated with full scapular rotation, i.e. in high elevation of the arm
above with the deep cervical fascia. It unites the superior aspect of the above shoulder height.


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In this position, the tension developed in the anterior sternoclavicu orly by the acromioclavicular ligament and the fibres of the attachment
lar ligament and anterior component of the costoclavicular ligament of trapezius, posteriorly by the fibres of attachment of trapezius, and
causes the clavicle to undergo an obligatory posterior translation. It also anteriorly by the fibres of attachment of deltoid. The inferior capsule is
acts as a checkrein on further rotation and displacement, so protecting often incomplete in later life.
the relatively weaker posterior sternoclavicular ligament from overload.
Although the function of subclavius is unknown, a consideration of the Ligaments There are two sets of associated ligaments. The intrinsic
simple biomechanics of forceful elevation of the arm above shoulder ligaments are the acromioclavicular ligaments; the extrinsic ligaments
height suggests that this muscle has an important role in decelerating are the coracoclavicular ligaments.
the elevating arm, so protecting the medial ‘clavicular–costal–sternal’
ligamentous structures from recurrent stretching that is likely to acceler Acromioclavicular ligaments The superior acromioclavicular ligament
ate degeneration and injury. The common innervation of the sternocla is quadrilateral. It extends between the upper aspects of the lateral end
vicular joint (the deep afferent–mechanoceptor system) and subclavius of the clavicle and the adjoining acromion. Its parallel fibres interlace
suggests an intimate functional relationship between these structures. with the aponeuroses of trapezius and deltoid. The inferior acromio
In daily activities, in which the upper limb is used largely in front of clavicular ligament is thin, and often perforated in later life; it extends
the trunk, the sternal end of the clavicle glides on the sternal facet about between the inferior surface of the lateral end of the clavicle and the
the fulcrum provided by the costoclavicular ligament. All joints in adjoining acromion. It provides attachment for the intraarticular disc
which polyaxial gliding occurs, producing shear forces (rotation with when this is present and complete.
translation), possess either intraarticular synovial bursae or intra


articular fibrocartilaginous discs; the latter degenerate over time, pro Coracoclavicular ligament The coracoclavicular ligament connects the
ducing characteristic exophytic degenerative arthritis. In this context, it clavicle and the coracoid process of the scapula (Fig. 48.16). Though
is interesting that degeneration of the sternoclavicular joint and ossifica separate from the acromioclavicular joint, it is an efficient and impor
tion of the costoclavicular ligaments (claviculocostal synostosis) are tant accessory ligament because it helps to maintain the apposition of
almost exclusively found in females above the age of 50 years. the acromion to the clavicle, and so contributes to the suspension
mechanism of the scapula (see above). The trapezoid and conoid parts
of the ligament, usually separated by fat or, frequently, by a bursa,
ACROMIOCLAVICULAR JOINT connect the posterior (more horizontal) part of the coracoid process
and the lateral end of the subclavian groove of the clavicle: these adja
The acromioclavicular joint is a synovial plane joint and has an intra cent areas may even be covered by cartilage to form a coracoclavicular
articular fibrocartilaginous disc. joint.
The trapezoid part is anterolateral and is broad, thin and quadrilat
Articulating surfaces The articulating surfaces are between the eral, ascending slightly from the upper coracoid surface to the trapezoid
acromial end of the clavicle and the medial acromial margin (Fig. line on the inferior clavicular surface. Its anterior border is free, and its
48.15). The joint is approximately plane but either surface may be posterior border is joined to the conoid part, forming an angle that
slightly convex, the other being reciprocally concave; both surfaces are projects backwards and upwards. Quadrilateral ligaments twist when
covered by fibrocartilage. The clavicular surface is a narrow, oval area the adjoined bones rotate with respect to each other, and as they twist,
that faces laterally or inferolaterally and overlaps a corresponding facet the apposed surfaces must approach each other; such ligaments, there


on the medial acromial border. The long axis is anteroposterior fore, act to oppose excessive rotation of the adjoining bones.
(ColegateStone et al 2010). The conoid part is posteromedial and is a dense, almost vertical,
triangular or conical band. Its broader base is attached superiorly to the
Fibrous capsule The capsule completely surrounds the articular conoid tubercle of the clavicle; its inferior apex is attached posteromedi
margins. It is lined by synovial membrane and is strengthened superi ally to the dorsal surface and root of the coracoid process immediately
Tendon of biceps brachii, long head Acromioclavicular ligament Fig. 48.15 The interior of the left shoulder
joint, anterolateral aspect. (With permission
from Waschke J, Paulsen F (eds), Sobotta
Trapezoid ligament Coraco-acromial ligament Atlas of Human Anatomy, 15th ed, Elsevier,
Subacromial bursa Urban & Fischer. Copyright 2013.)
Coracohumeral ligament
Supraspinatus
Subclavius
Pectoralis major
Deltoid
Pectoral fascia
Acromion
Pectoral fascia, opening for
cephalic vein
Conoid ligament
Tip of coracoid process Infraspinatus
Coracobrachial bursa
Joint capsule
Pectoralis minor
Biceps brachii, short head
Teres minor
Coracobrachialis
Subtendinous bursa of subscapularis Glenoid cavity
Subscapularis Glenoid labrum
Triceps brachii, long head


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Coraco-acromial ligament
Trapezoid ligament
Clavicle
Conoid ligament
Superior transverse Subscapularis bursa
scapular ligament
Acromioclavicular
ligament
Coracohumeral
ligament
Superior gleno-
humeral ligament
Opening of
subscapularis bursa
Transverse humeral
ligament
Lesser tubercle
Biceps tendon,
long head
Latissimus dorsi
Pectoralis major
Capsule dependent in adduction
Transverse humeral
Middle glenohumeral ligament
ligament
Fibrous capsule of shoulder joint Synovial sheath
of biceps brachii
Inferior glenohumeral ligament
A B
Fig. 48.16 A, The ligaments associated with the left shoulder, anterior aspect. B, A deeper view, showing the subscapularis bursa.
lateral to the scapular notch, and is contiguous with the superior trans are known collectively as the scapulothoracic articulation. Scapular
verse scapular ligament. Conical ligaments are constructed to oppose movements on the thoracic wall are facilitated by loose areolar tissue
distraction; the conoid ligament, therefore, helps to keep the coracoid between subscapularis and serratus anterior, and between serratus an
and the clavicle closely apposed. If the trapezoid ligament is disrupted, terior and the chest wall; the latter gliding plane is the scapulothoracic
the conoid ligament forms a vertical fulcrum around which the cora joint. It is a virtual space. There may be a bursa between the superior
coid can rotate under the clavicle, particularly if the acromioclavicular angle of the scapula and the dorsal aspect of the second rib.
ligaments are also disrupted. This is the anatomical basis for the spec The following account should be read together with the description
trum of acromioclavicular joint dislocation. of movements of the glenohumeral joint. It is important to keep in
mind the fact that the purpose of scapular motion is the appropriate
Articular disc The articular disc is a complete fibrocartilaginous positioning of the glenohumeral joint in space, and the purpose of


partition in juvenile and adolescent joints, creating medial and lateral scapular stability is to provide a foundation for glenohumeral motion.
compartments; over time, the centre of the disc perforates, and in adults
(more than 20 years old), it is often incomplete inferiorly. Elevation and depression
Vascular supply The acromioclavicular joint receives its arterial
Scapular elevation, as in ‘shrugging the shoulders’, is generated by tra
supply from branches of the suprascapular and thoracoacromial
pezius acting on the lateral clavicle, acromion and spine of the scapula.
arteries.
If levator scapulae is less active, the scapula rotates laterally (i.e. the
inferior angle protracts around the chest wall), with dorsal rotation at
Innervation The acromioclavicular joint is innervated by branches
the acromioclavicular joint; this is resisted by the rhomboid muscles
from the suprascapular and lateral pectoral nerves. It has been suggested
and controlled by pectoralis minor. If levator scapulae is more active,
that the density of nociceptors is greatest in the inferior acromioclavicu
then the scapula ascends with less rotation. The sternal end of the
lar ligament and capsule.
clavicle, rotating about an anteroposterior axis through the bone above
the medial attachment of the costoclavicular ligament, slides down over
Factors maintaining stability The acromioclavicular ligaments
the articular disc. This is resisted by subclavius and by tension in the
provide the greatest resistance to anteroposterior displacement of the
costoclavicular ligament and sternoclavicular joint capsule. In scapular
acromioclavicular joint, while the coracoclavicular ligaments resist rota
depression, ventral rotation occurs at the acromioclavicular joint, and
tion and vertical translation of the joint.
the clavicle slides up on the disc at the sternoclavicular joint. The move
ments are checked by the cervical fibres of trapezius, the interclavicular
Movements Movements at the joint complement those of the ster
and superior sternoclavicular ligaments and the articular disc. Usually,


noclavicular joint (Figs 48.17–48.20). The sternal end of the clavicle is
gravity alone is sufficient; when necessary, the lowest part of serratus
robustly supported by strong ligaments, and a similar, but less robust,
anterior and pectoralis minor are active depressors.
arrangement of ligaments suspends the scapula from the lateral end of
the bone. The motion of the acromioclavicular joint is limited by its
Protraction and retraction
small surface area and the articular capsule.
Protraction (forward movement) round the thoracic wall occurs in
MOVEMENTS AT THE SCAPULOTHORACIC ‘JOINT’ pushing, thrusting and reaching movements, usually with some lateral
rotation. The acromion advances over the clavicular facet to the limit,
The sternoclavicular and the acromioclavicular joints, in combination and the shoulder is simultaneously advanced by forward movement of
with the fascial space between the scapula and underlying chest wall, the lateral end of the clavicle and posterior translation of its sternal end


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The three long nerves innervating the scapulothoracic ‘joint’, i.e.
accessory, long thoracic and dorsal scapular, innervate the three major
muscle groups of scapulothoracic motion, namely: trapezius, serratus
anterior and the medial scapular stabilizing muscles (levator scapulae
and the rhomboids).


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Fig. 48.17 Clavicular motion about the medial fulcrum
of the sternoclavicular joint. The lateral (acromial) end of
10
the clavicle describes an asymmetric conical path
30˚ during motion of the upper extremity. The maximal
range of rotation of the clavicle (subtended by the
3
sternoclavicular joint) is 30°; the maximal range of
rotation of the scapula (sternoclavicular and
acromioclavicular joints combined) is about 60° with
respect to the sternum. The scapula is suspended from
the distal clavicle at the acromioclavicular joint, which
can be considered as the true joint (the cavity bounded
50˚ by the acromioclavicular capsule and ligaments); it is
30˚ also part of an extended articulation that comprises the
true joint and the coracoclavicular suspensory
ligaments. Arguably, the ligaments might be better
3
10 defined as the claviculocoracoid ligaments, to
acknowledge their role as the spiroid fulcrum around
which the body of the scapula, and therefore the
glenoid fossa, rotate during protraction and retraction of
the scapula. The action of subclavius is to resist upward
Subclavius Coracoclavicular ligament
displacement of the distal clavicle, or to decelerate the
clavicle moving into elevation. Linear measurements are
given in centimetres.
Costoclavicular
ligament
Fig. 48.18 The distal clavicle is moved by
trapezius, which has an extensive attachment
along the spine of the scapula and the medial
aspect of the distal third of the clavicle. The
antagonist of trapezial power is pectoralis minor,
which, rarely, has an extension or slip of tendon
that joins the coraco-acromial ligament. The latter
acts as a tension band between the ‘outriggers’ of
the acromion and coracoid. If surgically divided,
Trapezius the cut surfaces of the coraco-acromial ligament
cannot be readily reapposed, suggesting a
mechanical role in pre-tensioning the acromion


and coracoid against the pull of trapezius.
Shortening or tightness of pectoralis minor will
create fixed protraction of the scapula, which then
rotates ventrally around the chest wall. As a
consequence, the acromion tilts and the space
between it and the cranial surface of the rotator
cuff below (the subacromial space) diminishes,
creating the conditions in which forceful coaptation
of the apposed surface of the rotator cuff and the
coraco-acromial ligament may occur. This is the
Costoclavicular
painful condition of ‘impingement’.
ligament
Coraco-acromial ligament
Coracoclavicular ligament
Subclavius
Pectoralis minor
over the sternal facet, carrying the disc with it. Pectoralis major, together also acts like a strap across the inferior scapular angle in protraction
with the anterior sternoclavicular ligament and posterior lamina of the and lateral rotation.
costoclavicular ligament, check backward slide of the sternal end. Ser In scapular retraction, i.e. bracing back the shoulders, these move
ratus anterior and pectoralis minor are prime movers and maintain ments are reversed and checked at the sternoclavicular joint by the
continuous apposition of the scapula, especially its medial border, in posterior sternoclavicular ligament and anterior lamina of the costo
smooth gliding on the thoracic wall, with the rhomboid muscles con clavicular ligament. Trapezius (horizontal and lower fibres) and the
trolling the rate and range of motion. The upper part of latissimus dorsi rhomboids are prime movers.


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Fig. 48.19 Motion of the medial border of the
scapula is governed by the opposing actions of
the medial parascapular group (levator scapulae
and rhomboids minor and major) and the
Levator scapulae scapulothoracic group (serratus anterior), causing
Rhomboid minor retraction and protraction, respectively.
Rhomboid major
Costoclavicular
ligament
Coraco-acromial ligament
Coracoclavicular ligament
Serratus anterior
Fig. 48.20 The closely related humeral
attachments of pectoralis major and deltoid
(between one-third and one-half of the way down
the shaft of the bone) enable the pectoralis
major–deltoid muscular envelope to move the
elbow, forearm and hand in space, using the
shoulder as a fulcrum for effective delivery of
Trapezius
power through a wide range of motion from in
Deltoid front of the trunk to behind. The relative
coarseness of these muscles underlies their ability
to produce great torque in upper-extremity
motion; motion generated by these muscles is
‘fine-tuned’ by the rotator cuff working
concordantly with the outer envelope (each
segment or part of the rotator cuff can be said to
have an equivalent segment or part in the outer
envelope of muscles; this pattern is considered as
a force-couple generating stable motion of the
humerus on the scapula at the glenoid).
Coraco-acromial ligament
Pectoralis major (clavicular head)
Pectoralis minor
Pectoralis major (sternal head)


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Lateral and medial rotation Articulating surfaces The articular surfaces are reciprocally curved
and are correctly termed ovoids. The surface area of the humeral convex
Lateral (upward) rotation of the scapula increases the range of humeral ity is approximately four times that of the glenoid concavity, which
elevation by turning the glenoid cavity to face almost directly up, e.g. means that only a small portion of the head opposes the glenoid in any
when raising the arm above the head. This movement is always associ position (Fig. 48.22). The radius of curvature of the glenoid fossa in
ated with humeral elevation and rotation at the glenohumeral joint, the coronal plane is greater than that of the humeral head, and is deep
and with protraction of the scapula. Scapular rotation requires move ened by a fibrocartilaginous rim, the glenoid labrum (see Fig. 48.15;
ment at both sternoclavicular and acromioclavicular joints; the sterno Fig. 48.23). Both articular surfaces are covered by hyaline cartilage,
clavicular joint permits elevation of the lateral end of the clavicle, a thickest centrally and thinner peripherally over the humerus, and vice
movement that is almost complete when the arm is abducted to 90°. versa over the glenoid cavity. In most positions, their curvatures are not
The acromioclavicular joint moves in the first 30° of abduction, when fully congruent and the joint is loosepacked; closepacking (full con
the conoid ligament becomes taut, and is subsequently accompanied gruence) is probably only reached with the humerus abducted and
by clavicular rotation at the sternoclavicular joint around the longitu laterally rotated.
dinal axis of the bone. The medial end is depressed further as the lateral
end continues to rise. Some acromioclavicular movement also occurs Glenoid labrum The glenoid labrum is a fibrocartilaginous rim
in the final stages of humeral abduction. Trapezius (cervical fibres) and around the glenoid fossa. Anteriorly, it is triangular in section; posteri


serratus anterior (the lower part) are prime movers, with the rhomboids orly, it is more ovoid; while inferiorly, it may be flattened and almost
providing resistance to motion. deficient. It varies in size and thickness. The attachment to the edge of
Medial (downward) rotation is usually effected by gravity; gradual the glenoid fossa is secure superiorly where it blends with the anterior
active lengthening of trapezius and serratus anterior is sufficient to and posterior fasciculi of the long tendon of biceps (Vangsness et al
control it. When more force is needed, levator scapulae, the rhomboids 1994), less secure posteriorly, but relatively more secure anteroinferi
and, in the initial stages, pectoralis minor are prime movers in returning orly (Bankart 1923). There may be an aperture between the free deep
the scapula to a position of rest. edge of the labrum and the anterior glenoid rim above the midpoint
of the fossa. In slightly less than onefifth of normal shoulders, there
may be no anterior labrum, in which case its place taken by a cordlike
GLENOHUMERAL (SHOULDER) JOINT middle glenohumeral ligament. The labrum may be hypoplastic or
absent in patients with collagen deficiency but with normal shoulder
The glenohumeral joint is a synovial multiaxial spheroidal joint between function (hypermobility syndrome); these shoulders are not necessarily
the roughly hemispherical head of the humerus and the shallow glenoid unstable. The labrum deepens the glenoid cavity and so may assist in
fossa of the scapula (Fig. 48.21). It is the most mobile joint in the body stabilizing the humeral head on the fossa, although the mechanism of
and the most frequently dislocated. Its anatomy is a compromise this function remains uncertain. It may protect the bone and probably
between the requirements for motion and stability; both depend on the assists lubrication.
surrounding muscular and soft tissue envelope more than on the shape
and surface area of the articulating surfaces. Fibrous capsule A fibrous capsule envelops the joint (see Figs 48.16,


The humeral head is held to the concave glenoid fossa by the com 48.22). It is attached medially to the glenoid neck at a variable distance
pressive action of the rotator cuff muscles; the stabilizing mechanism from the glenoid labrum, so forming recesses anterior and posterior to
of the glenohumeral joint is one of concavity compression. The rotator the scapular neck; it includes the supraglenoid tubercle, to which the
cuff muscles are attached to the proximal humerus through a musculo long head of biceps attaches, and which is therefore intracapsular. Lat
tendinous envelope (see below), the deep surface of which fuses with erally, it is attached to the anatomical neck of the humerus, i.e. near the
the lateral part of the articular fibrous capsule. The humeral head is then articular margin, except inferomedially, where it descends more than
contained in a spherical space bounded medially by the glenoid fossa 1 cm on the calcar humerale. The fibres of the capsule are orientated in
and elsewhere by the deep surface of the fibrous capsule, a form of a spiral fashion, so that, in elevation of the arm, the capsule tightens,
osseofibrous acetabulum. The walls of this ‘acetabulum’ (i.e. the rotator so bringing the articular surfaces into closer apposition and contribut
cuff muscles and tendons) are contained within a roughly spherical ing to the concavity compression. In some individuals, a deeper band
space bounded by the coracoid anteriorly; the coracoacromial ligament of fibres orientated in a reverse obliquity to the main capsular fibres
anterosuperiorly; the acromion and spine of the scapula posteriorly, passes from the region of the lesser tubercle to the lower part of the
posterosuperiorly and posterolaterally; and the deep surface of deltoid anterior rim of the glenoid fossa. This is the anterior oblique band; its
anterolaterally and laterally. This arrangement creates two gliding contribution to stability is uncertain.
planes, one internal (the glenohumeral articular gliding plane) and one The lateral part of the external surface of the fibrous capsule is


external (the subcoracoid–subacromial–subdeltoid plane); the latter is blended with the tendons of supraspinatus (superiorly), infraspinatus
continuous with the plane under the scapula (the scapulothoracic and teres minor (posteriorly), subscapularis (anteriorly) and by the
gliding plane). Gliding is facilitated by the synovial lined cavities of the tendon of the long head of triceps at the infraglenoid tubercle (inferi
glenohumeral joint and the subcoracoid, subacromial and subdeltoid orly). The rotator interval is a medially based, triangular area of uncov
bursae, which are nearly always contiguous. Infection, inflammation ered capsule between the superior edge of subscapularis and the anterior
and injury commonly cause adhesions and fibrosis (with subsequent edge of supraspinatus, with the base of the coracoid as the medial
contracture) in these planes; restriction of motion follows, specific to boundary of the interval. It is reinforced by the coracohumeral liga
the site and extent of adhesion. The surfaces of both gliding planes are ment, the superior glenohumeral ligament, and fibres from the suprasp
extensive and fibrosis is consequently very restricting. inatus tendon laterally. The axillary nerve and posterior circumflex
3 5 4 Fig. 48.21 Radiographs of the left shoulder of
3
an 18-year-old female. A, Anteroposterior
5 view. B, Axillary view with the arm abducted.
Key: 1, head of humerus; 2, acromion;
4 3, clavicle; 4, acromioclavicular joint;
2 2 5, coracoid process; 6, glenoid fossa;
7, glenohumeral articulation.
1
1
7
6
6
A B


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A
Supraspinatus
Clavicular facet
Coracohumeral
Acromion
ligament 1
Biceps brachii, 2 6
long head, Subacromial
tendon bursa
Glenoidal
labrum 7
Glenoid
cavity
3
8
Head
Scapula 4
Intertubercular
tendon sheath 5
Axillary recess Biceps brachii,
long head,
tendon
A
Humerus
7
1
8
B 2
Supraspinatus
Acromion 3
Subacromial bursa
9
Tendon of biceps brachii, long head
4
Deltoid
10
5
Axillary nerve
6
11
Posterior circumflex B
humeral artery and
venae comitantes
Fig. 48.23 MRI of the shoulder. A, Axial T1 weighted view. Key: 1,
deltoid; 2, coracobrachialis; 3, glenoid; 4, subscapularis; 5, infraspinatus;
6, tendon of the long head of biceps; 7, head of humerus; 8, posterior
labrum. B, Median sagittal oblique image at the base of the coracoid.
Quadrangular space
Key: 1, clavicle; 2, supraspinatus; 3, coracoid; 4, subscapularis; 5, axillary
artery; 6, latissimus dorsi; 7, trapezius; 8, scapular spine; 9, infraspinatus;
10, deltoid; 11, triceps. Compare A with Figure 48.46.
Teres major
Profunda brachii humeral vessels are separated from the inferior capsule by the inferior
artery and
border of subscapularis. The capsule is least supported inferiorly, and
venae comitantes
subjected to the greatest strain in full abduction, when it is stretched
Radial nerve tightly across the humeral head. It is supported in this position by the
proximal part of the long head of triceps and the broad bulk of teres


Triceps brachii, major.
long head There are two openings in the capsule: below the coracoid process,
connecting the joint cavity to a bursa that may envelop the upper border
Unossified (cartilaginous) region Circumflex scapular artery of the tendon of subscapularis (anteriorly); and between the humeral
and venae comitantes tubercles, allowing passage of the long tendon of biceps and its synovial
Fig. 48.22 Coronal sections through the left shoulder joint, posterior sheath.
aspect. A, Anterior view. B, Posterior view. Note the subacromial bursa
and contents of the quadrangular space. (A, With permission from Ligaments The ligaments associated with the glenohumeral joint are
Waschke J, Paulsen F (eds), Sobotta Atlas of Human Anatomy, 15th ed, the glenohumeral (superior, middle and inferior), coracohumeral and
Elsevier, Urban & Fischer. Copyright 2013.) transverse humeral. A ligament only restricts a specific motion of a joint
when discrete parts of the ligament become tight; this only occurs at
the limits of a specific motion of the joint when the ligament acts as a
‘checkrein’. For movements that lie within the limit of motion, liga
ments have no mechanical role. Mechanoreceptors and nociceptors are
clustered at each end of the ligaments, more on the glenoid side than
the humeral side (Halata and Baumann 2008). The capsule, ligaments


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Superior glenohumeral Biceps brachii tendon, which blend with the capsule, to the greater and lesser tubercles (see
ligament long head Fig. 48.16). Portions of the coracohumeral ligament form a tunnel for
the biceps tendon on the anterior side of the joint. The rotator interval
is reinforced by the coracohumeral ligament. It also blends inferiorly
with the superior glenohumeral ligament. The ligament tightens in
external rotation of the glenohumeral joint.
Transverse humeral ligament The transverse humeral ligament is a
broad band that passes between the humeral tubercles, and is attached
superior to the epiphysial line (see Fig. 48.16). It converts the inter
tubercular sulcus into a canal, and acts as a retinaculum for the long
tendon of biceps.
Synovial membrane The synovial membrane lines the capsule and
covers parts of the anatomical neck. The long tendon of biceps brachii
traverses the joint in a synovial sheath that continues into the inter
tubercular sulcus as far as the surgical neck of the humerus (see Figs
48.16, 48.22A). The intraarticular bicipital sheath may be connected
to the articular surface of the superior capsule above by a mesotenon,
which may be incomplete, presenting as one or several strands. This
arrangement can only be the case if the biceps tendon was originally
an extraarticular structure and invaginated, with its synovial sheath,
into the glenohumeral joint as the upper limb rotated into external
rotation relative to the trunk during development.
Bursae Many bursae adjoin the shoulder joint (see Fig. 48.16). They
are usually found between the tendon of subscapularis and the capsule,
communicating with the joint between the superior and middle gleno
humeral ligaments; on the superior acromial aspect; between the cora
coid process and capsule; between teres major and the long head of
Middle glenohumeral Anterior inferior Posterior glenohumeral triceps; and anterior and posterior to the tendon of latissimus dorsi.


ligament glenohumeral ligament ligament The subacromial bursa, between deltoid and the capsule, does not com
Fig. 48.24 A sagittal magnetic resonance arthrogram image following municate with the joint cavity but is prolonged under the acromion
distension of the glenohumeral joint by intra-articular contrast injection in and coracoacromial ligament, and between them and supraspinatus:
a 28-year-old male. Note the clearly outlined glenohumeral ligaments. it appears to be attached, together with the subdeltoid fascia, to the
acromion. Bursae sometimes occur behind coracobrachialis and
between the tendon of infraspinatus and the capsule, occasionally
and labrum contain the deep afferent innervation of the glenohumeral opening into the joint.
joint and therefore contribute to stability of the joint through facilita
tion of the rotator cuff activity within the normal range of human Vascular supply The glenohumeral joint is supplied by branches
shoulder motion. from the anterior and posterior circumflex humeral, suprascapular and
circumflex scapular vessels.
Glenohumeral ligaments Three glenohumeral ligaments, only visible
from within the joint, reinforce the capsule anteriorly and inferiorly Innervation The glenohumeral joint is innervated mainly from the
(Fig. 48.24). The superior glenohumeral ligament passes from the sup posterior cord of the brachial plexus through the subscapular nerves.
raglenoid tubercle, just anterior to the origin of the long head of biceps, The capsule is supplied by the suprascapular nerve (posterior and supe
to the humerus at the fovea capitis, near the proximal tip of the lesser rior parts), axillary nerve (anteroinferior) and the lateral pectoral nerve
tubercle on the medial ridge of the intertubercular sulcus. It forms an (anterosuperior, including the rotator interval capsule).
anterior cover around the long head of biceps and is part of the rotator
interval. Together with the coracohumeral ligament, it is an important Factors maintaining stability The articulation between the


stabilizer in the inferior direction, helping to keep the humeral head relatively large humeral head and the shallow glenoid fossa allows
suspended (the coracohumeral ligament is more robust than the super a wide range of movement but is a challenge for the stability of
ior glenohumeral ligament). the joint.
The middle glenohumeral ligament arises from a wide attachment
below the superior glenohumeral ligament, along the anterior glenoid
margin as far as the inferior third of the rim, and passes obliquely MOVEMENTS AT THE GLENOHUMERAL JOINT
inferolaterally, enlarging as it does so, to attach to the lesser tubercle
deep to the tendon of subscapularis, with which it blends. The width The shoulder is capable of any combination of swing and spin over a
and thickness of this ligament may be as much as 2 cm and 4 mm, range far wider than that of any other joint in the body. Flexion–
respectively. It provides anterior stability between 45° and 60° of extension, abduction–adduction, and medial (internal) and lateral
abduction in the scapular plane. However, 30% of individuals may not (external) rotation all occur at the shoulder. A combination of all of
have a middle glenohumeral ligament; these individuals are not more these results in the motion of circumduction, which is not a useful
likely to have unstable shoulders. It may be thickened and cordlike in movement to record in clinical practice. Although the majority of the
the Buford complex (a congenital glenoidal labrum variant), again with movement of the shoulder occurs at the glenohumeral joint, the
no apparent disadvantage for stability. scapulothoracic articulation contributes to overall shoulder motion in
The thicker and longer inferior glenohumeral ligament complex is a all directions, including lateral rotation.
hammocklike structure with anchor points on the anterior and pos
terior sides of the glenoid. It arises from the anterior, middle and Muscles producing movements The muscles that produce move
posterior margins of the glenoid labrum, below the epiphysial line, and ments at the glenohumeral joint are principally the scapulohumeral and


passes anteroinferiorly to the inferior and medial aspects of the neck of thoracobrachial muscles: deltoid, pectoralis major and latissimus dorsi,
the humerus. The anterior, superior edge of the inferior ligament is assisted by coracobrachialis. The translating effect of these muscles on
thickened as the anterior band; there is an equivalent, but not so robust, the shoulder joint is counteracted by the rotator cuff, a group of short
thickening of the posterior capsule: the posterior band. Between the two muscles (subscapularis, supraspinatus, infraspinatus and teres minor),
bands is a region of thin capsule known as the axillary pouch. (For including teres major, that are attached closer to the joint, and that
further details, consult Burkart and Debski (2002); Di Giacomo et al centre the head of the humerus in the glenoid fossa through the entire
(2008).) range of motion.
Coracohumeral ligament The coracohumeral ligament is attached to Flexion Flexion is carried out by pectoralis major (clavicular part),
the dorsolateral base of the coracoid process and extends as two bands, deltoid (anterior fibres) and coracobrachialis, assisted by biceps. The


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In anatomical analysis of shoulder movements, it is usual to relate said to be 10° and scapular movement 5°, but this ratio is not linear
humeral movement to the scapula, rather than to conventional ana throughout the range of motion. During the initial stages of abduction,
tomical planes. However, in clinical practice, movements are related to the entire rotator cuff counteracts the strong upward component of the
the conventional anatomical planes. When the arm hangs at rest, the pull of deltoid, which would otherwise cause the humeral head to slide
glenoid fossa faces almost equally forwards and laterally, and the up the glenoid surface; the additive turning moments exerted by the
humeral capitular and scapular (topographical) axes correspond, combined deltoid and supraspinatus forcecouple may then abduct the
although the humerus, relative to the anatomical position, is medially arm. Deltoid also acts with the other elements of the rotator cuff,
rotated. With the humerus in the anatomical position, i.e. with the according to the position of the arm in space, to maintain rotation,
interepicondylar axis in the frontal plane, the humeral head axis is flexion and extension of the arm. It is important to consider the syner
posteriorly directed, in line with the axis of the scapula. gistic relation between the rotator cuff and deltoid as a continuum in
Using the anatomical description, flexion carries the arm antero which the rotator cuff muscles act to provide a stable base on which
medially on an axis through the humeral head orthogonal to the deltoid can work effectively, whatever the position of the arm.
glenoid fossa at its centre. Abduction and adduction occur in a vertical In flexion, the humerus swings at right angles to the scapular plane,
plane orthogonal to that of flexion–extension and the axis is horizontal, and scapular rotation cannot increase the elevation (120°) that is
through the humeral head and parallel with the glenoid plane. Pure obtainable in full flexion. If the fully flexed humerus is also abducted,


abduction raises the arm anterolaterally in the plane of the scapula. elevation increases pro rata until, when the humerus reaches the scapu
However, when referred to the trunk, flexion and extension occur in the lar plane, i.e. when true abduction is reached, 180° of elevation becomes
paramedian plane, and abduction and adduction occur in the coronal possible. In medial or lateral rotation, the humerus revolves about one
plane. In this sense, raising the arm vertically from flexion or raising it quarter of a circle around a vertical axis; the range is greatest when the
from abduction are both accompanied by humeral rotation in opposite arm is pendant, and least when it is vertical. When the rotational range
directions. Whether ‘scapular’ or any other plane of abduction is at the glenohumeral joint is assessed, the forearm should be flexed to
described, these are selections from an infinite series. In scapular abduc a right angle at the elbow in order to prevent the effects of superadded
tion, points on the humeral surface pursue vertical cords, but in rota pronation or supination in the pendant limb. In circumduction, which
tion, they are horizontal. In ‘pure’ flexion–extension, in a plane is a succession of the foregoing movements, the distal end of the
orthogonal to the scapula, the axis of movement and the notional humerus describes the base of a cone with its apex at the humeral head.
‘mechanical axis’ are regarded as projected from the centre of the This glenohumeral movement may be greatly increased by scapular
glenoid cavity. movements, e.g. in acts of slinging objects with force.
Glenohumeral abduction is about 120° or more (see p. 831; see The peculiar relation of the long head of biceps brachii to the shoul
Fig. 48.21). Abduction may reach 180° after thoracoscapular arthrod der joint may serve several purposes. By its connection with both the
esis for facioscapulohumeral dystrophy (Copeland and Howard 1978). shoulder and elbow, the muscle harmonizes their actions as an elastic


Abduction is restricted to about 45° after glenohumeral arthrodesis. connection during all upper limb movements. It helps to prevent the
Some 60° of further abduction occurs at the sterno and acromiocla humeral head impinging on the acromion when deltoid contracts and
vicular articulations, and contralateral vertebral flexion also aids in also to steady it in movements of the arm. In paralysis or absence (i.e.
bringing the arm to the vertical. During active elevation, movements at in rotator cuff tendon tears) of supraspinatus, the long head of biceps
the glenohumeral and acromioclavicular joints are simultaneous, may also help initiate abduction of the arm, particularly when the
except in the initial few degrees, when most, often all, movement is humerus is laterally rotated.
glenohumeral. For every 15° of elevation, glenohumeral movement is


Shoulder girdle and arm
816
6
noiTCeS
sternocostal part of pectoralis major is a major force in flexion forwards example, both subscapularis and pectoralis major generate medial rota
to the coronal plane from full extension. tion of the glenohumeral joint; subscapularis contributes to concavity
compression at the glenohumeral joint (i.e. stability), while pectoralis
Extension Extension is carried out by deltoid (posterior fibres) and major causes anterior displacement into flexion and adduction in the
teres major, from the dependant position. When the fully flexed arm is absence of subscapularis; when these muscles are working synergisti
extended against resistance, latissimus dorsi and the sternocostal part cally, the arm is both stabilized at the glenohumeral joint, and flexed
of pectoralis major act powerfully until the arm reaches the coronal and adducted.
plane. The clinical examination of the shoulder girdle muscles is demon
strated in Video 46.1.
Abduction Abduction is carried out by supraspinatus and deltoid. The
effect of deltoid is mainly upward and, unless opposed, this would
MUSCLES OF SCAPULAR SUSPENSION
displace the humerus upwards. Subscapularis, supraspinatus, infrasp
inatus and teres minor exert a centralizing force and so apply a balanc
ing force; together with deltoid, they constitute a ‘couple’ to produce Trapezius acts on the spine of the scapula, acromion and lateral clavicle
abduction in the scapular plane. to rotate the acromioclavicular joint upwards and dorsally; movement
is guided and limited by the length and shape of the clavicle. Pectoralis
Medial rotation Medial rotation is carried out by pectoralis major, minor acts to control the position of the coracoid as trapezius acts on
deltoid (anterior fibres), latissimus dorsi, teres major and, with the arm the scapula, while subclavius acts to control clavicular elevation and
pendant, subscapularis. rotation. These muscles act on the processes of the scapula, while the


coracoacromial ligament acts as a tension band between the processes.
Lateral rotation Lateral rotation is carried out by infraspinatus, deltoid Disruption of the continuity of this arrangement (fracture of the clavicle
(posterior fibres) and teres minor. Lateral rotation is important for or coracoid, or dislocation of the acromioclavicular joint) will have a
clearance of the greater tubercle and its associated tissues as it passes profound effect on scapular suspension.
under the coracoacromial arch during elevation of the arm.
Trapezius
Glenohumeral joint dislocation The glenohumeral joint is the Trapezius is derived from head paraxial mesenchyme with neural crest
most frequently dislocated joint in the body. The vast majority of dis connective tissue, rather than from the dermomyotomes of lower
locations are anterior, and occur when the forearm is forced backwards somites, and is therefore unique among shoulder girdle muscles. It is
into greater lateral (external) rotation when it is in abduction, lateral attached to the spine of the scapula and acromion, segments of the
rotation and extension. A dislocated shoulder loses its normal contour scapula for which development is encoded by a single gene (804.e1).
because the humeral head is displaced anterior to the glenoid rim and,
sometimes, under the coracoid, which means that the acromion process, Attachments Trapezius is a flat, triangular muscle that extends over
rather than the greater tubercle, becomes the most lateral bony struc the back of the neck and upper thorax (see Fig. 53.16). The paired
ture, affording the shoulder a ‘squaredoff’ appearance. trapezius muscles form a diamond shape, from which the name is
derived. On either side, the muscle is attached to the medial third of
the superior nuchal line, external occipital protuberance, ligamentum
MUSCLES
nuchae, and apices of the spinous processes and their supraspinous
ligaments from C7 to T12. The occipital attachment is by a fibrous
The shoulder girdle and shoulder joint musculature are arranged in lamina, which is also adherent to the skin. The spinal attachment is by