scapula scapula the scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). like their connected bones, the scapulae are paired, with each scapula on either side of the body being roughly a mirror image of the other. the name derives from the classical latin word for trowel or small shovel, which it was thought to resemble. scapulathe upper picture is an anterior (from the front) view of the thorax and shoulder girdle. the lower picture is a posterior (from the rear) view of the thorax (scapula shown in red.)detailsidentifierslatinscapula (omo)meshd012540ta98a02.4.01.001ta21143fma13394anatomical terms of bone in compound terms, the prefix omo- is used for the shoulder blade in medical terminology. this prefix is derived from ὦμος (ōmos), the ancient greek word for shoulder, and is cognate with the latin (h)umerus, which in latin signifies either the shoulder or the upper arm bone. the scapula forms the back of the shoulder girdle. in humans, it is a flat bone, roughly triangular in shape, placed on a posterolateral aspect of the thoracic cage. structure the scapula is a thick, flat bone lying on the thoracic wall that provides an attachment for three groups of muscles: intrinsic, extrinsic, and stabilizing and rotating muscles. the intrinsic muscles of the scapula include the muscles of the rotator cuff—the subscapularis, teres minor, supraspinatus, and infraspinatus. these muscles attach to the surface of the scapula and are responsible for the internal and external rotation of the shoulder joint, along with humeral abduction. the extrinsic muscles include the biceps, triceps, and deltoid muscles and attach to the coracoid process and supraglenoid tubercle of the scapula, infraglenoid tubercle of the scapula, and spine of the scapula. these muscles are responsible for several actions of the glenohumeral joint. the third group, which is mainly responsible for stabilization and rotation of the scapula, consists of the trapezius, serratus anterior, levator scapulae, and rhomboid muscles. these attach to the medial, superior, and inferior borders of the scapula. the head, processes, and the thickened parts of the bone contain cancellous tissue; the rest consists of a thin layer of compact tissue. the central part of the supraspinatus fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin in humans as to be semitransparent; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue. the scapula has two surfaces, three borders, three angles, and three processes. surfaces 3d model of scapula, along with annotations showing the various parts of the scapula front or subscapular fossa the front of the scapula (also known as the costal or ventral surface) has a broad concavity called the subscapular fossa, to which the subscapularis muscle attaches. the medial two-thirds of the fossa have 3 longitudinal oblique ridges, and another thick ridge adjoins the lateral border; they run outward and upward. the ridges give attachment to the tendinous insertions, and the surfaces between them to the fleshy fibers, of the subscapularis muscle. the lateral third of the fossa is smooth and covered by the fibers of this muscle. at the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the center of the glenoid cavity, forming a considerable angle, called the subscapular angle; this gives greater strength to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. the costal surface superior of the scapula is the origin of 1st digitation for the serratus anterior origin. figure 1 : left scapula. costal surface. subscapular fossaglenoid cavitycoracoid processacromionsuperior borderscapular notchsuperior anglemedial borderinferior anglelateral borderinfraglenoid tubercle back the back of the scapula (also called the dorsal or posterior surface) is arched from above downward, and is subdivided into two unequal parts by the spine of the scapula. the portion above the spine is called the supraspinous fossa, and that below it the infraspinous fossa. the two fossae are connected by the spinoglenoid notch, situated lateral to the root of the spine. the supraspinous fossa, above the spine of scapula, is concave, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds give origin to the supraspinatus. at its lateral surface resides the spinoglenoid fossa which is situated by the medial margin of the glenoid. the spinoglenoid fossa houses the suprascpular canal which forms a connecting passage between the suprascapular notch and the spinoglenoid notch conveying the suprascapular nerve and vessels. the infraspinous fossa is much larger than the preceding; toward its vertebral margin a shallow concavity is seen at its upper part; its center presents a prominent convexity, while near the axillary border is a deep groove which runs from the upper toward the lower part. the medial two-thirds of the fossa give origin to the infraspinatus; the lateral third is covered by this muscle. there is a ridge on the outer part of the back of the scapula. this runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm above the inferior angle. attached to the ridge is a fibrous septum, which separates the infraspinatus muscle from the teres major and teres minor muscles. the upper two-thirds of the surface between the ridge and the axillary border is narrow, and is crossed near its center by a groove for the scapular circumflex vessels; the teres minor attaches here. the broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the teres muscles from each other. its lower third presents a broader, somewhat triangular surface, the inferior angle of the scapula, which gives origin to the teres major, and over which the latissimus dorsi glides; frequently the latter muscle takes origin by a few fibers from this part. figure 2 : left scapula. dorsal surface. supraspinous fossaspineinfraspinous fossasuperior bordersuperior anglemedial borderinferior anglelateral borderlateral angleacromioncoracoid processorigin of teres major muscleorigin of teres minor muscle side the acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first laterally, and then curving forward and upward, so as to overhang the glenoid cavity. figure 3 : left scapula. lateral surface. coracoid processglenoid cavitysupraspinous fossaacromioninfraspinous fossainferior anglelateral border angles there are 3 angles: the superior angle of the scapula or medial angle, is covered by the trapezius muscle. this angle is formed by the junction of the superior and medial borders of the scapula. the superior angle is located at the approximate level of the second thoracic vertebra. the superior angle of the scapula is thin, smooth, rounded, and inclined somewhat lateralward, and gives attachment to a few fibers of the levator scapulae muscle. the inferior angle of the scapula is the lowest part of the scapula and is covered by the latissimus dorsi muscle. it moves forwards round the chest when the arm is abducted. the inferior angle is formed by the union of the medial and lateral borders of the scapula. it is thick and rough and its posterior or back surface affords attachment to the teres major and often to a few fibers of the latissimus dorsi. the anatomical plane that passes vertically through the inferior angle is named the scapular line. the lateral angle of the scapula or glenoid angle also known as the head of the scapula is the thickest part of the scapula. it is broad and bears the glenoid fossa on its articular surface which is directed forward, laterally and slightly upwards, and articulates with the head of the humerus. the inferior angle is broader below than above and its vertical diameter is the longest. the surface is covered with cartilage in the fresh state; and its margins, slightly raised, give attachment to a fibrocartilaginous structure, the glenoidal labrum, which deepens the cavity. at its apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the biceps brachii is attached. the anatomic neck of the scapula is the slightly constricted portion which surrounds the head and is more distinct below and behind than above and in front. the surgical neck of the scapula passes directly medial to the base of the coracoid process. superior angle shown in red lateral angle shown in red anatomic neck: red, surgical neck: purple inferior angle shown in red borders there are three borders of the scapula: the superior border is the shortest and thinnest; it is concave, and extends from the superior angle to the base of the coracoid process. it is referred to as the cranial border in animals. at its lateral part is a deep, semicircular notch, the scapular notch, formed partly by the base of the coracoid process. this notch is converted into a foramen by the superior transverse scapular ligament, and serves for the passage of the suprascapular nerve; sometimes the ligament is ossified. the adjacent part of the superior border affords attachment to the omohyoideus. costal surface of left scapula. superior border shown in red. left scapula. superior border shown in red. animation. superior border shown in red. the axillary border (or "lateral border") is the thickest of the three. it begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. it is referred to as the caudal border in animals. it begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity, about 2.5 cm (1 in). in length, which gives origin to the long head of the triceps brachii; in front of this is a longitudinal groove, which extends as far as the lower third of this border, and affords origin to part of the subscapularis. the inferior third is thin and sharp, and serves for the attachment of a few fibers of the teres major behind, and of the subscapularis in front. dorsal surface of left scapula. lateral border shown in red. left scapula. lateral border shown in red. animation. lateral border shown in red. the medial border (also called the vertebral border or medial margin) is the longest of the three borders, and extends from the superior angle to the inferior angle. in animals it is referred to as the dorsal border. four muscles attach to the medial border. serratus anterior has a long attachment on the anterior lip. three muscles insert along the posterior lip, the levator scapulae (uppermost), rhomboid minor (middle), and to the rhomboid major (lower middle). left scapula. medial border shown in red. animation. medial border shown in red. still image. medial border shown in red. levator scapulae muscle (red) rhomboid minor muscle (red) rhomboid major muscle (red) development figure 5 : plan of ossification of the scapula. from seven centers. the scapula is ossified from 7 or more centers: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle. ossification of the body begins about the second month of fetal life, by an irregular quadrilateral plate of bone forming, immediately behind the glenoid cavity. this plate extends to form the chief part of the bone, the scapular spine growing up from its dorsal surface about the third month. ossification starts as membranous ossification before birth. after birth, the cartilaginous components would undergo endochondral ossification. the larger part of the scapula undergoes membranous ossification. some of the outer parts of the scapula are cartilaginous at birth, and would therefore undergo endochondral ossification. at birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border and the inferior angle are cartilaginous. from the 15th to the 18th month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the bone about the 15th year.