BACKGROUND: Instability after shoulder arthroplasty remains a complication with limited salvage options. Reoperation for instability with anatomic designs has led to high rates of persistent instability, therefore we aimed to evaluate the use of RSA for treatment of prosthetic instability.
QUESTIONS/PURPOSES: (1) After revision shoulder arthroplasty to a reverse prosthesis (RSA), what is the survivorship free from dislocations at 2 and 5 years? (2) What factors are associated with dislocations? (3) What is the survivorship free from revision after revision to RSA? (4) From preoperation to postrevision to RSA, what are the clinical outcomes-the proportion of patients with moderate to severe pain, shoulder elevation and external rotation ROM, American Shoulder and Elbow Surgeons scores, and Simple Shoulder Test scores?
METHODS: All shoulder arthroplasties revised for prosthetic instability using RSA components between January 2004 and July 2014 were retrospectively studied. During the period in question, we performed 82 revisions for instability of an anatomic total shoulder arthroplasty (TSA) (n = 62), hemiarthroplasty (n = 13), or reverse TSA (n = 7). We typically used a reverse TSA to treat this problem, but we identified 12 treated in other ways, including revision of a TSA to hemiarthroplasty (n = 3), revision of a reverse TSA to hemiarthroplasty (n = 2), revision of hemiarthroplasty to a hemiarthroplasty (n = 1), and revision of an anatomic TSA to another anatomic TSA (n = 6). This left 70 patients for evaluation; of those, 65 (93%) were available for analysis at a mean of 3 years (range, 2-10 years). A total of seven patients died. Eight of the 65 shoulders were not evaluated during the last 5 years, including three in patients who died earlier. The mean age of the patients at the time of revision RSA was 65 years (range, 40-89 years). Data were obtained from a longitudinally maintained institutional joint registry. Instability was defined as severe subluxation confirmed on clinical and radiographic examinations. We evaluated pain and ROM, and Kaplan-Meier curves were used to estimate survivorship.
RESULTS: The survivorship free from dislocation at 2 and 5 years was 87% (95% CI, 80%-94%) and 79% (95% CI, 67%-91%) respectively, with 10 of 65 (15%) patients having an episode of dislocation after revision surgery. Persistent instability was more common in those with a BMI greater than 35 kg/m(hazard ratio [HR], 5; 95% CI, 2-16; p = 0.008) and prior hemiarthroplasty (HR, 5; 95% CI, 2-16; p = 0.005), whereas patients who had undergone a previous TSA were less likely to have persistent instability (HR, 0.08; 95% CI, 0.0-0.30; p < 0.001) The survival free from rerevision for any indication at 2 and 5 years was 85% (95% CI, 76%-94%) and 78% (95% CI, 66%-90%) respectively; with the numbers available, we were not able to find associated factors. Fewer patients had moderate or severe pain after revision to RSA (preoperative: 48 of 65 [74%]; postoperative: nine of 65 [14%]; p < 0.001). After surgery, patients showed improvement in shoulder elevation (preoperative: 42° [± 30°], postoperative: 112° [42°]; mean difference, 70° [95% CI, - 83to 57°]; p < 0.001) and external rotation (preoperative: 20° [± 22°], postoperative: 42° [± 23°]; mean difference, 22° [95% CI, - 30° to - 14°]; p < 0.001). American Shoulder and Elbow Surgeons scores improved (preoperative: 21 [± 10], postoperative: 68 [± 14], mean difference, 46 [95% CI, - 58 to - 35]; p < 0.001); where a higher score is better. Simple Shoulder Test scores also improved (preoperative: 2/12 [± 2], postoperative: 7/12 [± 3]; mean difference, 5 [95% CI, - 7 to - 2.17]; p < 0.001); where a higher score is better. 2o
CONCLUSIONS: Revision RSA for prosthetic instability after shoulder arthroplasty is associated with reasonable implant survival and few complications. Approximately one in seven patients will have a recurrent dislocation. In patients with persistent instability or with risk factors for instability, consideration should be given for use of larger glenospheres and increasing the lateral offset at the time of RSA.
LEVEL OF EVIDENCE: Level IV, therapeutic study.
