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We used a dynamic shoulder-testing apparatus and nine fresh-frozen, entire upper extremities from cadavera to evaluate the effects of varying degrees of capsulolabral injury on the kinematics of the glenohumeral joint during abduction in the scapular plane and external rotation. Joint kinematics were recorded with use of a six-degrees-of-freedom magnetic tracking device before and after the creation of each capsulolabral lesion in a progressive manner. Dislocation did not occur after simulation of a large Bankart lesion or even after sectioning of the anterior aspect of the joint capsule. However, division of the entire joint capsule (that is, both the anterior aspect and the posterior aspect) resulted in a significant increase (p < 0.05) in posterior translation during abduction in the scapular plane, and two of the nine shoulders dislocated posteriorly. External rotation of the abducted extremity produced no increase in anterior or posterior translation.CLINICAL RELEVANCE: We concluded that dynamic stability can be maintained by the rotator-cuff muscles even when the anterior aspect of the capsule is divided and the anterior portion of the labrum is separated. Thus, anterior glenohumeral instability is a complex phenomenon that may include a combination of muscle imbalance and capsulolabral injury. Our findings suggest that the importance of the active stabilizers of the glenohumeral joint should be considered when capsulolabral injuries and defects are reconstructed and when rehabilitation regimens are formulated.