The microscopic pathoanatomy of acute anterior shoulder dislocations in a simian model.

PURPOSE: The purpose of this study was to determine the extent of capsular injury that occurs at a microscopic level in association with acute anterior shoulder dislocations.

TYPE OF STUDY: The study was an anatomic, cadaveric study using a simian model. The microscopic slide review was blinded regarding the presence or absence of dislocation.

METHODS

Three cadaveric monkey shoulder specimens were dissected free of muscle tissue but left undislocated as controls. Eleven cadaveric monkey shoulder specimens were dislocated with an abduction and external rotation force and subsequently evaluated grossly and histologically for the presence and direction of gross and microscopic injury.

RESULTS

All dislocated specimens had an associated Bankart lesion. In addition, all dislocated specimens had histologic evidence of capsular microtearing. The tears were in no specific location or direction and were at times located perpendicular to, obliquely to, or between the longitudinal orientation of the fibers.

CONCLUSIONS

Based on this model, a Bankart lesion is a common and usual occurrence with acute anterior shoulder dislocations. In these specimens, the Bankart lesion was never an isolated pathology. Microscopic capsular injury was always associated. Additionally, the direction of the capsular injury is highly variable.