Background: Patients with irreparable rotator cuff tears have a defect of the superior capsule, which creates discontinuity of the shoulder capsule in the transverse direction (anterior-posterior direction). This effect is one of the causes underlying shoulder instability after rotator cuff tears. Purpose/Hypothesis: The purpose of this study was to assess the effects of anterior and posterior continuity on shoulder biomechanics after superior capsule reconstruction (SCR). The hypothesis was that capsular continuity in the transverse direction would improve glenohumeral stability after SCR. Study Design: Controlled laboratory study. Methods: Seven fresh-frozen cadaveric shoulders were tested by using a custom shoulder testing system. Subacromial peak contact pressure, glenohumeral superior translation, glenohumeral compression force, and glenohumeral range of motion (ROM) were compared among 5 conditions: (1) intact shoulder, (2) simulated irreparable supraspinatus tendon tear, (3) SCR without side-to-side suturing, (4) SCR with posterior side-to-side suturing, and (5) SCR with both anterior and posterior side-to-side suturing. Results: The creation of an irreparable supraspinatus tear significantly increased glenohumeral superior translation (0 degrees of abduction: 254% of intact [P = .04]; 30 degrees of abduction: 200% of intact [P = .04]) and subacromial peak contact pressure (0 degrees of abduction: 302% of intact [P = .0001]; 30 degrees of abduction: 239% of intact [P = .0006]), decreased glenohumeral compression force (0 degrees of abduction: 85% of intact [P = .004]; 30 degrees of abduction: 87% of intact [P = .0002]; 60 degrees of abduction: 88% of intact [P = .0001]), and increased total ROM (0 degrees of abduction: 16 degrees increase [P = .008]). SCR without side-to-side suturing significantly decreased subacromial peak contact pressure (0 degrees of abduction: 79% of intact [P = .0001]; 30 degrees of abduction: 91% of intact [P = .001]; 60 degrees of abduction: 55% of intact [P = .04]) but did not inhibit glenohumeral superior translation. By adding posterior side-to-side sutures, both glenohumeral superior translation (0 degrees of abduction: 93% of intact [P = .02]; 30 degrees of abduction: 110% of intact [P = .04]) and subacromial peak contact pressure decreased significantly (0 degrees of abduction: 56% of intact [P = .0001]; 30 degrees of abduction: 83% of intact [P = .0003]; 60 degrees of abduction: 46% of intact [P = .04]). Neither SCR with nor SCR without side-to-side suturing ameliorated the tear-associated decrease in glenohumeral compression force and increase in total ROM. Adding anterior side-to-side sutures did not change any measurements compared with SCR with posterior side-to-side suturing. Conclusion: SCR with side-to-side suturing completely restored the superior stability of the shoulder joint by establishing posterior continuity between the graft, residual infraspinatus tendon, and underlying shoulder capsule. Clinical Relevance: Side-to-side suturing between the graft, residual infraspinatus tendon, and underlying shoulder capsule is recommended for SCR in patients with irreparable supraspinatus tendon tears to restore superior stability after surgery.
