Increased superior translation following multiple simulated anterior dislocations of the shoulder

Abstract

PurposeRecurrent shoulder dislocations can result in kinematic changes of the glenohumeral joint. The number of prior shoulder dislocations may contribute to increased severity of capsulolabral lesions. The kinematics of the glenohumeral joint following multiple dislocations remain poorly understood. The purpose of this study was to assess the kinematics of the glenohumeral joint during anterior dislocations of the shoulder, and more specifically, altered translational motion following multiple dislocations. The kinematics of the glenohumeral joint were hypothesized to change and correlate with the number of dislocations. MethodsEight fresh‐frozen cadaveric shoulders were dissected free of all soft tissues except the glenohumeral capsule. Each joint was mounted in a robotic testing system. At 60 degrees of glenohumeral abduction, an internal and external rotational torque (1.1 Nm) were applied to the humerus, and the resulting joint kinematics were recorded. Anterior forces were applied to the humerus to anteriorly dislocate the shoulder and the resulting kinematics were recorded during each dislocation. Following each dislocation, the same rotational torque was applied to the humerus, and the resulting joint kinematics were also recorded. A repeated‐measures analysis of variance (ANOVA) was used to compare the kinematics following each dislocation. ResultsDuring the 7th, 8th, 9th, and 10th dislocations, the humerus significantly translated superiorly compared with the shoulder during the 1st dislocation (p < 0.05). Following the 3rd, 4th, 5th, and 10th dislocations, the humeral head significantly translated superiorly compared with the shoulder following the 1st dislocation in the position of 60 degrees of abduction in response to external rotation torque (p < 0.05). ConclusionMultiple anterior shoulder dislocations lead to abnormal translational kinematics and result in increased superior translation of the humerus. This may contribute to pathologic superior extension of capsulolabral injuries. Superior translation of the humerus with overhead motion in the setting of recurrent instability may also place the shoulder at risk for extension of the capsulolabral injuries.

Glenohumeral morphological predictors of recurrent shoulder instability following arthroscopic Bankart repair

“…The glenohumeral joint is the most commonly dislocated joint in the body, most often dislocating anteriorly and inferiorly as a result of force applied to the arm in external rotation and abduction or direct impact to the shoulder itself [13,29,44]. Anterior shoulder instability is a frequent cause of injury, with incidence rates as high as 15% having been reported in rugby players [13].…”