Differences in 3-dimensional shoulder kinematics between persons with multidirectional instability and asymptomatic controls

Background: Evidence that persons with multidirectional instability (MDI) of the shoulder have abnormal shoulder kinematics is limited. A kinematic description of scapulothoracic and glenohumeral motion can assist both conservative and surgical rehabilitative programs. Hypothesis: Persons with MDI of the shoulder demonstrate increased anterior and inferior glenohumeral translation and decreased scapular upward rotation and increased scapular internal rotation compared with age-matched and gender-matched asymptomatic controls. Study Design: Controlled laboratory study. Methods: Sixty-two subjects were recruited from an outpatient orthopaedic clinic. Subjects with MDI were matched according to age, gender, and hand dominance to asymptomatic controls. An electromagnetic motion capture system evaluated the 3-dimensional position of the trunk, scapula, and humerus during frontal and scapular plane elevation. A repeated measures analysis of variance evaluated joint positions and glenohumeral translations during 4 phases of elevation (0°-30°, 31°-60°, 61°-90°, and 91°-120°). Results: When averaged across the 4 phases of elevation, persons with MDI demonstrated a significant decrease in scapular upward rotation in scapular plane abduction (8°, P =.006) and abduction (5.8°, P =.016) and increased internal rotation during scapular plane abduction (12.2°, P =.03). Alterations in glenohumeral translations in the MDI group did not reach statistical significance (P =.54-.71). Conclusion: Abnormal scapular kinematics are seen in the MDI shoulder, highlighting the importance of incorporating scapular positioning and stability exercises during rehabilitation. Additional study is warranted concerning the efficacy of various rehabilitation programs, and also both surgical and nonsurgical interventions in this population.