Kinematic analysis of dynamic shoulder motion in patients with reverse total shoulder arthroplasty.

BACKGROUND: Reverse total shoulder arthroplasty (rTSA) has been used to treat patients with irreparable rotator cuff dysfunction. Despite the proven clinical efficacy, there is minimal information regarding the underlying changes to the shoulder kinematics associated with this construct. Therefore, we sought to examine the kinematics of dynamic shoulder motion in patients with well-functioning rTSA. METHODS: We tested 12 healthy subjects and 17 patients with rTSA. All rTSA patients were able to elevate their arms to at least 90° and received the implant as the primary arthroplasty at least 6 months before testing. On average, the rTSA patients elevated their arms to 112° ± 12° (mean ± SD) and reported an American Shoulder and Elbow Surgeons outcome score of 90.6 ± 6.3. A 3-dimensional electromagnetic motion capture device was used to detect the dynamic motion of the trunk, scapula, and humerus during bilateral active shoulder elevation along the sagittal, scapular, and coronal planes. RESULTS: In both healthy and rTSA shoulders, the majority of the humeral-thoracic motion was provided by the glenohumeral motion. Therefore, the ratio of glenohumeral to scapulothoracic (ST) motion was always greater than 1.62 during elevation along the scapular plane. In comparison to healthy subjects, however, the contribution of ST motion to overall shoulder motion was significantly increased in the rTSA shoulders. This increased contribution was noted in all planes of shoulder elevation and was maintained when weights were attached to the arm. CONCLUSION: Kinematics of the rTSA shoulders are significantly altered, and more ST motion is used to achieve shoulder elevation.

Reverse shoulder arthroplasty in patients with rheumatoid arthritis.

BACKGROUND: The purpose of this study was to describe the pathoanatomy of patients diagnosed with rheumatoid arthritis and rotator cuff deficiency and report their outcomes following reverse shoulder arthroplasty. METHODS: Twenty-one shoulders were evaluated prospectively. Nine had no prior surgery, 9 had a failed rotator cuff repair, and 3 had a failed arthroplasty. Patients were followed for a minimum of 2 years (average, 36 months). All patients had preoperative radiographs and 19 shoulders had an MRI or CT available for evaluation of muscular and bony deficiency. Radiographs at most recent follow-up were evaluated for loosening and scapular notching. RESULTS: All outcome measures improved significantly: ASES scores improved from 28 preoperatively to 82 postoperatively (P < .0001); SST scores improved from 1 to 7 (P < .0001); VAS pain scores improved from 7 to 1 (P < .0001); VAS function scores improved from 3 to 6 (P=.0058); elevation improved from 52° to 126° (P < .0001); abduction improved from 55° to 116° (P=.0002); external rotation improved from 19° to 33° (P=.02); and internal rotation improved from S1 to L4 (P=.02). Twelve patients rated their outcome as excellent, 6 as good, 2 as satisfactory, and 1 as unsatisfactory. Severe glenoid erosion was seen in 10 of the shoulders and 5 of the defects required structural grafting. Three patients (14%) sustained a complication that required reoperation: 2 for infection and 1 for periprosthetic fracture. CONCLUSIONS: In patients with rheumatoid arthritis and rotator cuff deficiency, reverse shoulder arthroplasty can provide improvement in function and decreased pain.