Qingxiang Hu1, Zhenyu Ding1, Haoyu Zhang2, Yaohua He3. 1. Department of Sports Medicine, Shanghai Jiaotong University Affiliated Sixth People's Hospital, Shanghai, People's Republic of China. 2. Department of Biostatistics, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland, U.S.A. 3. Department of Sports Medicine, Shanghai Jiaotong University Affiliated Sixth People's Hospital, Shanghai, People's Republic of China. Electronic address: heyaohua@sjtu.edu.cn.
Abstract
PURPOSE: To answer 2 questions: What is the main structure that prevents the superior translation of the humeral head, the supraspinatus or the superior capsule (SC)? And what mechanism does the principal structure rely on to prevent the superior translation of the humeral head, the spacer effect or the tensional hammock effect? METHODS: Eight shoulder specimens were assessed using a custom biomechanical testing system. Glenohumeral superior translation and subacromial peak pressure were compared using 6 models: the intact joint model, supraspinatus dysfunction model, supraspinatus defect model, SC tear model, SC defect model, and irreparable rotator cuff tear (IRCT) model. RESULTS: Compared with the intact joint model, the supraspinatus defect model significantly increased the superior translation (by 2.6 mm; P < .001) and subacromial peak pressure (by 0.43 MPa; P = .013) at 0° glenohumeral abduction, while the SC defect model unremarkably altered the superior translation at 0° (by 0.6 mm; P = .582) and 45° (by 0.3 mm; P = .867) of glenohumeral abduction and the subacromial peak pressure at 0° (by 0.11 MPa; P = .961), 30° (by -0.03 MPa; P = .997), and 45° (by -0.33 MPa; P = .485) of glenohumeral abduction. The supraspinatus dysfunction model significantly increased the superior translation at 0° (by 1.7 mm; P < .001), 30° (by 1.2 mm; P = .005), and 45° (by 0.8 mm; P = .026) of glenohumeral abduction, but not the subacromial peak pressure compared with the intact joint model. However, no significant differences were found between the supraspinatus defect model and the supraspinatus dysfunction model with respect to the superior translation or subacromial peak pressure (all P > .05). CONCLUSIONS: The anatomic SC has a negligible role in preventing the superior translation of the humeral head. CLINICAL RELEVANCE: SC reconstruction is not a simple anatomic reconstruction, and its promising clinical outcome may be due to tensional fixation technique and choice of graft.
PURPOSE: To answer 2 questions: What is the main structure that prevents the superior translation of the humeral head, the supraspinatus or the superior capsule (SC)? And what mechanism does the principal structure rely on to prevent the superior translation of the humeral head, the spacer effect or the tensional hammock effect? METHODS: Eight shoulder specimens were assessed using a custom biomechanical testing system. Glenohumeral superior translation and subacromial peak pressure were compared using 6 models: the intact joint model, supraspinatus dysfunction model, supraspinatus defect model, SC tear model, SC defect model, and irreparable rotator cuff tear (IRCT) model. RESULTS: Compared with the intact joint model, the supraspinatus defect model significantly increased the superior translation (by 2.6 mm; P < .001) and subacromial peak pressure (by 0.43 MPa; P = .013) at 0° glenohumeral abduction, while the SC defect model unremarkably altered the superior translation at 0° (by 0.6 mm; P = .582) and 45° (by 0.3 mm; P = .867) of glenohumeral abduction and the subacromial peak pressure at 0° (by 0.11 MPa; P = .961), 30° (by -0.03 MPa; P = .997), and 45° (by -0.33 MPa; P = .485) of glenohumeral abduction. The supraspinatus dysfunction model significantly increased the superior translation at 0° (by 1.7 mm; P < .001), 30° (by 1.2 mm; P = .005), and 45° (by 0.8 mm; P = .026) of glenohumeral abduction, but not the subacromial peak pressure compared with the intact joint model. However, no significant differences were found between the supraspinatus defect model and the supraspinatus dysfunction model with respect to the superior translation or subacromial peak pressure (all P > .05). CONCLUSIONS: The anatomic SC has a negligible role in preventing the superior translation of the humeral head. CLINICAL RELEVANCE: SC reconstruction is not a simple anatomic reconstruction, and its promising clinical outcome may be due to tensional fixation technique and choice of graft.