Biomechanical Studies Of Superior Capsule Reconstruction

ObjectiveThe biomechanical study aimed to explore(1)the nature of the superior capsule reconstruction and(2)the biomechanical effects of the modified superior capsule reconstruction.Methods and materialsIn the first part,specimens were prepared into six models: intact glenohumeral joint,supraspinatus dysfunction,supraspinatus removal,superior capsule tear,superior capsule removal,and irreparable rotator cuff tear.The glenohumeral superior translation and subacromial peak pressure were compared among six models to examine if the superior capsule played an important role in preventing superior translation of the humeral head,further exploring if the superior capsule reconstruction is an anatomic reconstruction.In the second part,specimens were prepared into four models: intact glenohumeral joint,irreparable rotator cuff tear,superior capsule reconstruction and modified superior capsule reconstruction.The glenohumeral superior translation and subacromial peak pressure were compared among four models to examine if the modified superior capsule reconstruction could prevent the superior translation of the humeral head and to make a comparison of biomechanics between superior capsule reconstruction and the modified one.ResultsIn the first part,the removal of the supraspinatus significantly increased the superior translation(by 2.6 mm;P < 0.001)and the subacromial peak pressure(by 0.43 MPa;P = 0.013)when compared with the intact glenohumeral joint at 0° glenohumeral abduction.However,the removal of the superior capsule unremarkably increased the superior translation(by 0.6 mm;P = 0.582)and the subacromial peak pressure(by 0.11 MPa;P = 0.961)when compared with the intact glenohumeral joint at 0° glenohumeral abduction.In the second part,the modified superior capsule reconstruction significantly decreased the superior translation(by 2.3 mm;P = 0.002)and the subacromial peak pressure(by 0.65 MPa;P < 0.001)when compared with the intact glenohumeral joint at 0° glenohumeral abduction.Additionally,there were no significant differences in the superior translation or the subacromial peak pressure between the superior capsule reconstruction and the modified one.ConclusionThe superior capsule does not play a primary role in preventing the superior translation of the humeral head,indicating the superior capsule reconstruction is not an anatomic reconstruction.The modified one could prevent the superior translation and decrease the subacromial peak pressure.The biomechanical effects between the superior capsule reconstruction and the modified one are similar.