Rate of improvement in shoulder strength after anatomic and reverse total shoulder arthroplasty

Background: The rate at which patients regain shoulder strength after anatomic and reverse total shoulder arthroplasty (TSA) is unknown. In this study, we aimed to quantify differences in the timeline during which patients gained shoulder strength after primary anatomic and reverse TSA.

Methods: We retrospectively reviewed prospectively collected data from 374 shoulders after primary anatomic TSA (aTSA) and 601 shoulders after primary reverse TSA (rTSA). Postoperative improvement in external rotation (ER) strength and forward elevation (FE) strength from baseline was assessed at 3 months, 6 months, 1 year, and 2 years. Percent change in mean shoulder strength between each time point was determined for anatomic and reverse groups separately. A handheld dynamometer was used to assess ER strength with the involved shoulder in 0° ER, 0° abduction, and the elbow in 90° flexion and FE strength with the involved shoulder in the scapular plane at 30° of flexion and 30° of abduction.

Results: Both aTSA and rTSA groups ceased to have statistically significant gains in FE strength after 1 year postoperatively. In contrast, patients continued to have statistically significant gains in ER strength between 1 year and 2 years postoperatively after rTSA (P = .001), but not after aTSA (P = .476). Both aTSA and rTSA groups saw improvement in strength in both ER (+32.1% and +51.4%, respectively) and FE (+38.3% and +90.3%, respectively) at 2-year follow-up. The aTSA group's ER and FE strength increased the most between 3 and 6 months (+16.2% and +35.7%, respectively). In contrast, the rTSA group gained the most ER strength between 6 months and 1 year (+14.8%) and the greatest FE strength between baseline and 3 months (+40.3%).

Conclusion: Patients gain ER strength earlier and FE strength later after aTSA compared with rTSA. Most gains in strength occurred in the first year. However, statistically significant gains in shoulder ER strength in the rTSA group continued between 1 year and 2 years postoperatively, suggesting that 2-year follow-up may be inadequate to capture the full benefits of rTSA on shoulder strength. The results of this study provide insight into the timeline of strength recovery after aTSA and rTSA that will help inform patient counseling and future study design.