1. Posterior Shoulder Dislocation Disrupting Anatomical Structures
Alvin Mallia, Neil Ashwood, Mohammed Hassan
Trauma and Orthopaedics Department, Queens Hospital & Burton Hospital NHS Foundation Trust, Burton-on-Trent, UK
Case Presentation
We present a case of a 39 year old male, who sustained an impacting force to the anterior left shoulder, whilst falling from his push bike. X-Rays revealed a posterior dislocation of his left shoulder, with a comminuted fracture of the greater tuberosity. Closed reduction on the same day failed. During open reduction the humeral head was reconstructed, and an avulsed greater tuberosity and torn rotator cuff were simultaneously repaired. The patient made a full recovery without any long term sequelae.
Figure 1: AP view at presentation
Figure 2: Axillary view at presentation
Anatomical Considerations
Posterior dislocations comprise 2-4 % of all dislocations. They occur when there is a blow to the front of the shoulder, violent muscle contractions due to a seizure, electrocution, or the arm is bent across the body and pushed backwards.
The glenohumeral joint is the most mobile joint (1), and an inherently unstable one. The glenoid represents only approximately 25% to 30% of the articular surface the humeral head, and thus has a limited ability to confer substantial stability. The labrum overcomes this limitation to a certain extent by increasing the depth of the glenoid by approximately 50% (2). The posterior capsule provides static stability, and the muscles of the shoulder girdle as well as the rotator cuff provide dynamic stability. Two biomechanical studies (3,4) on cadavers subjected to posterior dislocation demonstrated lesions in the posterior capsule. In addition one of these studies also revealed concomitant tears of the tendons of teres minor and infraspinatus. An imaging study of patients who had sustained posterior glenohumeral dislocation demonstrated MRI evidence of injury to the teres minor in all patients, and half of the patients had a full-thickness rupture of this tendon (5).
Injuries that are commonly associated with posterior dislocation include fractures, reverse Hill–Sachs lesions, and rotator cuff tears as mentioned. In the case, failure of closed reduction was due to the humeral head being locked behind the glenoid, a large muscle bulk and reduction being blocked by bony fragments. Acute repair of the defect, as in our case presentation, facilitates a good outcome
Figure 3: A Final X ray in Theatre- reduced congruent joint.
References
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Hottya GA, Tirman PF, Bost FW, et al. Tear of the posterior shoulder stabilizers after posterior dislocation: MR imaging and MR arthrographic findings with arthroscopic correlation. AJR Am J Roentgen- ol 1998