A Comparison and Correlation of Clinical Outcome Metrics in Anatomic and Reverse Total Shoulder Arthroplasty.

INTRODUCTION Indications for anatomic (aTSA) and reverse (rTSA) total shoulder arthroplasty are well defined and dependent on the function of the rotator cuff; however, indications for rTSA have gradually extended to complex fractures, revisions, and primary arthritis in very elderly patients. The risk of secondary rupture of a weakened or degenerative rotator cuff is difficult to assess and can lead the orthopaedic surgeon to hesitate between aTSA or rTSA. It, therefore, seems appropriate to compare these two types of prostheses in terms of pain, functional, clinical outcome metric scores, and complications, despite suspected differences between populations and the respective diseases. METHODOLOGY 1,145 patients (69.2 ± 8.9 years) were treated by 12 orthopaedic surgeons in France and in the USA, using either aTSA or rTSA with one platform shoulder system. Five hundred twenty-eight patients received aTSA (66.2 ± 9.0 years; 283 female, 245 male) for treatment of degenerative arthritis, and 617 patients received rTSA (71.8 ± 8.0 years; 392 female, 225 male) for treatment of cuff tear arthroplasty, rotator cuff tear, and osteoarthritis. Each patient was scored preoperatively and at latest follow-up using the SST, UCLA, ASES, Constant, and SPADI metrics; active range of motion was also measured. The average follow-up for all patients was 39.7 ± 18.7 months (aTSA: 42.7 ± 21.9 months; rTSA: 37.1 ± 15.1 months). Improvements in outcome using each metric score were normalized on a 100 point scale, correlated, and compared. A Student's two-tailed, unpaired t-test was used to identify differences in preoperative, postoperative, and pre-to-postoperative improvements, where p < 0.05 denoted a significant difference. RESULTS Preoperatively, rTSA patients had significantly lower mean outcome scores and significantly lower mean active range of motion as compared to aTSA patients. Post-operatively, rTSA and aTSA patients showed no significant difference in active forward flexion or in mean outcome scores as measured by four of the five metrics. rTSA patients had significantly lower active abduction, internal rotation, and active and passive external rotation than aTSA patients. However, they had significantly better strength (9.7 vs. 7.3 lbs, p < 0.0001). Preoperative to postoperative mean improvements were compared between both cohorts. rTSA patients were associated with significantly larger improvements in outcomes and also had significantly better improvements in active forward flexion and strength. Conversely, aTSA patients had significantly better improvement in active and passive external rotation and active internal rotation. Analysis of complications demonstrated a very similar rate between cohorts, with aTSA patients associated with a slightly lower rate (6.6 vs. 7.3%). CONCLUSION This retrospective analysis of prospectively acquired data from 1,145 patients who received either a primary aTSA or rTSA prosthesis demonstrates that each device provides significant improvements with very similar mean results. In fact, the mean clinical outcomes associated with the reverse shoulder prostheses approach that of the "gold standard" anatomic device for their respective indications. Furthermore, the complication rates in this series are very similar and also favorable relative to the clinical literature. Findings, such as these, may at some point extend the indications of the reverse prosthesis to patients for whom an anatomical prosthesis could lead to a premature deterioration of the result.