Alterations in Glenohumeral Forces Following Rotator Cuff Injury and Repair

OBJECTIVES: Rotator cuff repair is associated with an unusually high incidence of osteoarthritic changes and cartilage damage in the glenohumeral joint. Such degeneration may be secondary to improper tensioning of muscular stabilizers during surgical intervention; however, existing studies have not specifically examined changes in joint congruity following rotator cuff repair. Therefore, the purpose of this study was to assess for changes in glenohumeral contact forces following the repair of rotator cuff injury. METHODS: Transduction mapping was performed on the glenohumeral joint of ten fresh-frozen cadaveric shoulder specimens. A calibrated pressure-mapping sensor was introduced through the rotator interval and secured along the concavity of the glenoid labrum. Following a baseline force measurements, analysis of force intensity and total glenohumeral contact area was performed in each specimen for 6 simulated injury and treatment conditions: A) A 1 cm supraspinatus lesion; B) 2-suture repair of the 1 cm lesion; C) removal of the 2-suture repair; D) a 2 cm supraspinatus lesion; E) 3-suture repair of the 2 cm lesion and; F) removal of the 3-suture repair. All repairs were performed via bone tunnels in the standard method described. Data were recorded over 60s intervals at a rate of 4 frames per second and included raw force, area, and force per unit area. Values for lesion, repair, and post-repair conditions were expressed as a proportion of initial baseline measurements. Means and standard deviations were then calculated for each condition and compared via Student’s t-tests. RESULTS: For baseline measurements, the mean intact glenohumeral force was 38.55 ± 24.79 N and the mean contact area was 313 ± 84.09 mm(2). In comparison to baseline values, 3-suture repair yielded a significant increase in both total glenohumeral force (mean proportion: 2.16 ± 3.26; p=0.046) as well as proportion of force per unit area (1.73 ± 1.86 N/mm2; p=0.024). Both the 2 cm lesion and the 2-suture repair removal yielded significant decreases in contact area when compared to baseline, with the former exhibiting a proportion of 0.76 ± 0.19 (p=0.040) and the latter yielding a proportion of 0.60 ± 0.29 (p=0.004). No other conditions exhibited significant changes from baseline measurements. CONCLUSION: Rotator cuff injury leads to alterations in glenohumeral forces, with significant increases in articular contact-pressures following repair of larger supraspinatus lesions. These findings offer a possible explanation for the high rate of degenerative changes demonstrated following rotator cuff repair. Further study is warranted to determine how current treatment methods might be improved to result in glenohumeral contact pressures resembling those experienced prior to injury.