Last Updated: February 01 2005
Fractures of the posterior glenoid rim and of the proximal humerus (upper shaft tuberosities and head) are quite common in traumatic posterior dislocations of the shoulder. (O'Conner 1956; O'Conner and Jacknow 1955; Thomas 1937; Wilson and McKeever 1949) The commonly associated compression fracture of the anteromedial portion of the humeral head is produced by the posterior cortical rim of the glenoid. It is best seen on an axillary view or a CT scan.
This lesion sometimes called a "reversed Hill-Sachs lesion often occurs at the time of the original posterior dislocation. It becomes larger with multiple posterior dislocations of the shoulder. Large humeral head defects are also seen in old unreduced posterior dislocations.
The posterior rim of the glenoid may be fractured and displaced in posterior dislocations. This occurs not only with direct forces from an anterior direction that push the humeral head out posteriorly, but also with indirect types of dislocations such as occur during seizures or accidental electrical shock.
Fracture of the lesser tuberosity of the humerus may accompany posterior dislocations. The subscapularis muscle comes under considerable tension in this dislocation and may avulse the lesser tuberosity onto which it inserts. Although the fracture may be seen on the anteroposterior and lateral x-rays of the glenohumeral joint, it is best seen on the axillary view and on CT scan.
Posterior dislocations of the humerus may be overlooked in the presence of comminuted fracture of the proximal humerus or humeral shaft fractures. In the series of 16 cases of posterior dislocation of the shoulder reported by O'Conner and Jacknow, (O'Conner and Jacknow, 1955) twelve had comminuted fractures of the proximal humerus. In 8 of the 12 cases of fracture, the diagnosis of posterior dislocation was initially missed.
Injuries to the rotator cuff and neurovascular structures are less common with posterior than anterior dislocations. However they do occur.
Moeller (Moeller 1975) reported on a patient who had an open acute posterior dislocation of the left shoulder. The shoulder was totally unstable following reduction with tears of the rotator cuff biceps tendon and subscapularis tendons. The patient had associated injury to the axillary and suprascapular nerves.