rotator cuff tears are very common injuries ; ruptures generally occur within the tendon or as an avulsion from the greater tuberosity [ 1 , 2 ] .
musculotendinous ruptures are common both in the upper and in the lower extremities ; ruptures of the rotator cuff through the musculotendinous junction are exceptional .
we describe a case of traumatic supraspinatus rupture at the musculotendinous junction in a 23-year - old woman , its clinical presentation , and the successful conservative treatment performed .
a healthy 23-year - old woman presented to our emergency department after a fall on her outstretched left arm , which was forced posterior to her back .
, there was tenderness over the supraspinatus fossa , no pain on palpation of the scapular body spine or the proximal humerus , and a full passive range of motion ( rom ) ; passive abduction was painful > 90. active abduction and forward flexion were impossible due to pain .
orally administered analgesics were prescribed , the arm was immobilized in a sling , and a magnetic resonance imaging ( mri ) to evaluate the rotator cuff was planned , which showed a complete lesion of the supraspinatus at the musculotendinous junction ( fig . 
a t1 short - tau inversion - recovery - weighted coronal view shows disruption of the musculotendinous junction of the supraspinatus with hematoma and edema involving the entire muscle belly ; the intramuscular septum is inhomogeneous and slackened ( arrow ) .
b proton density fat - saturated sagittal imaging at the level of the scapular y view shows a intramuscular hematoma in the posterior portion of the muscle belly and perimuscular edema .
c the intramuscular septum is clearly slackened on proton - density fat - saturated axial view ( arrow )   magnetic resonance imaging performed 1 day after trauma .
a t1 short - tau inversion - recovery - weighted coronal view shows disruption of the musculotendinous junction of the supraspinatus with hematoma and edema involving the entire muscle belly ; the intramuscular septum is inhomogeneous and slackened ( arrow ) .
b proton density fat - saturated sagittal imaging at the level of the scapular y view shows a intramuscular hematoma in the posterior portion of the muscle belly and perimuscular edema .
c the intramuscular septum is clearly slackened on proton - density fat - saturated axial view ( arrow ) the patient was treated conservatively with the arm immobilized in a sling at 45 of abduction and neutral rotation of the shoulder . at day 1 , the simple shoulder test ( sst ) score was 2 ( range 012 ) and constant score was 44 . after 25  days , passive elevation , abduction , and circumduction of the shoulder
, active abduction and forward elevation to 100 was attained : sst score was 8 and constant score 57 .
the patient started eccentric strengthening exercises . at day 60 , she had full rom , including complete abduction ; at this time , a repeat mri showed disappearance of the perimuscular edema and partial reorganization of the muscular architecture ( fig .  2).fig . 
a t1 short - tau inversion recovery coronal and b proton - density fat saturated sagittal views show reduction of the intra- and perimuscular edema , but a persistent small intramuscular area of high signal compatible with edema remained in the site of the lesion .
c proton - density fat - saturated axial view shows a more homogeneous and stretched intramuscular septum ( arrow )   magnetic resonance imaging performed 60  days after trauma . a t1 short - tau inversion recovery coronal and
b proton - density fat saturated sagittal views show reduction of the intra- and perimuscular edema , but a persistent small intramuscular area of high signal compatible with edema remained in the site of the lesion .
c proton - density fat - saturated axial view shows a more homogeneous and stretched intramuscular septum ( arrow ) at day 80 , the strength of the supraspinatus was restored to normal , sst score was 12 , and constant score was 100 .
mri performed 29  months after the trauma showed no edema and a restored intramuscular tendinous septum , but a hypotrophic muscle with a grade 1 fatty infiltration according to fuchs was visible ( fig . 
3 ) . at that time , the patient was healthy , without limitation in her activities , and maintained an sst score of 12 and a constant score of 100 .
a t1 short - tau inversion - recovery coronal image shows complete disappearance of edema , even though the muscle is hypotrophic .
b proton - density fat - saturated sagittal and c axial view confirms the reduction of muscle volume and shows a small intramuscular scar in the posterior side of the musculotendinous junction .
d grade 1 fatty degeneration clearly visible on t1 sagittal view ( arrow )   magnetic resonance imaging performed 29  months after trauma .
a t1 short - tau inversion - recovery coronal image shows complete disappearance of edema , even though the muscle is hypotrophic .
b proton - density fat - saturated sagittal and c axial view confirms the reduction of muscle volume and shows a small intramuscular scar in the posterior side of the musculotendinous junction .
to our knowledge , in the peer - reviewed literature there are only six cases of a traumatic rupture of the supraspinatus at the musculotendinous junction [ 4 , 5 ] .
our patient is the youngest reported with a rupture of the supraspinatus at the musculotendinous junction .
mean age of the six previously reported cases is 40  years ; anyway lower than the mean 55 years old found for a supraspinatus tendon tear or the mean 49 years old found for a musculotendinous rupture of the infraspinatus [ 2 , 6 ] .
musculotendinous injuries are common in the extremities but rare in the rotator cuff ; musculotendinous lesions of the supraspinatus are exceptional .
grade 3 injuries are complete rupture of the muscle fibers and generally occur at the musculotendinous junction . the acute phase of such lesions is characterized by widespread intra- and extramuscular edema and hematoma and complete disruption of the muscle ; these lesions heal with scar formation and generally muscle weakness .
rupture of the musculotendinous junction may occur at different strain rates according to muscle architecture and elongation .
consequently , their fibers are designed for force production rather than excursion : they are short and produce near - maximal active tension over a narrow range of sarcomere length . glenohumeral stability must be provided also with the muscles at rest or in extreme joint position ; for this reason , muscle fibers have long resting sarcomere lengths to produce adequate passive tension .
the combination of short fibers and long resting sarcomere length make the rotator cuff muscles relatively sensitive to stretch because of the low rate of myofilament overlap .
pennate muscle , such as the infraspinatus , are more susceptible to such injury ; for muscles with similar pennation angles but with differing fiber lengths , imposing a given stretch across the muscle will lengthen each sarcomere in a short fiber to a greater extent compared with those in a long fiber .
this finding is in agreement with the fact that musculotendinous rupture of the infraspinatus , a pennate muscle , is a recognized injury when rupture of the supraspinatus , a parallel - fibered muscle , is rare ; it remains to be understood .   in our case ,
supraspinatus rupture at the musculotendinous junction could have been caused by a sudden passive stretching of the supraspinatus because of the position of the arm during the fall .
when the arm is forced backward and adducted , the supraspinatus fibers are already maximally lengthened and passively stretched , so myofilament overlap is too low to permit muscle contraction .
it is well known that reflex muscle contraction is a defense mechanism to prevent or reduce the amount of damage caused by a given injury .
therefore , muscles that are actively contracting , particularly if eccentric , can resist to a greater force before musculotendinous unit failure than can passively stretched muscles .
another explanation for the rupture may be an acute inlet impingement at the acromioclavicular joint during the fall with the arm outstretched and forced backward .
the shape of the patient s acromion , type 2 according to bigliani , could support this mechanism , but absence of acromioclavicular osteoarthritis could make this mechanism unlikely . due to the unique case reported here , we are unable to recommend a treatment strategy for this type of lesion . in our case ,
conservative treatment showed a satisfactory outcome , leading to complete restoration of supraspinatus function in 80  days and an asymptomatic grade 1 fatty degeneration of the muscle belly on mri after 29  months .
this is in contrast with the previous study in which conservative treatment of full - thickness lesion led to the patient s dissatisfaction and grade 4 fatty infiltration on mri follow - up .
 the vast majority of rotator cuff tears occur within the tendon or as an avulsion from the greater tuberosity . 
 supraspinatus injury at the musculotendinous junction is a very uncommon event . 
 we describe a case of supraspinatus rupture at the musculotendinous junction , with successful conservative treatment . 
 it occurred in a 23-year - old woman , the youngest patient with this uncommon type of injury . to our knowledge , this is the first case of rupture of the supraspinatus muscle at the musculotendinous junction in a young woman and the second in a woman . 
Introduction
Case report
Discussion