Preoperative shoulder strength is associated with postoperative primary anatomic total shoulder arthroplasty outcomes and improvement

Background: Although numerous preoperative factors that influence postoperative outcomes after anatomic total shoulder arthroplasty (aTSA) have been identified, preoperative shoulder strength has not been studied. The purpose of this study was to determine whether preoperative shoulder strength is predictive of postoperative outcomes and improvement after primary aTSA.

Methods: We conducted a retrospective review of prospectively collected data from 160 shoulders with minimum 2-year follow-up after primary aTSA. Preoperative external rotation (ER) strength, supraspinatus strength, and abduction strength score were analyzed to determine their correlation with postoperative outcomes and improvement in shoulder strength, range of motion (ROM), and outcome scores. Multiple linear regression models were subsequently used to adjust for covariates and determine the preoperative measures of shoulder strength that most influenced postoperative outcomes and improvement.

Results: Preoperative ER strength, supraspinatus strength, and abduction strength score were each moderately correlated with their respective postoperative values and improvement (P < .001 for all). A decrease in ER strength, supraspinatus strength, and abduction strength score postoperatively was identified for preoperative strength values > 8.2 kg, > 6.6 kg, and > 4.5 kg, respectively. In contrast, no upper limit of preoperative shoulder strength led to a decrease in ROM or outcome scores postoperatively. On multivariate analysis, the baseline abduction strength score was a statistically significant predictor of postoperative values and improvement for all 3 measures of shoulder strength, raw and normalized Constant scores, and improvement in active abduction and active elevation.

Conclusion: Preoperative shoulder strength is moderately associated with postoperative outcomes and improvements in shoulder strength, ROM, and outcome scores after primary aTSA. It is important to note that we identified preoperative strength values that led to a decrease in strength postoperatively but not ROM or outcome scores. The results of our study demonstrate that abduction strength may be a useful indicator of patient outcomes after aTSA. Our findings will provide surgeons with useful prognostic insight to aid in guiding patient expectations.