Factors Predicting Postoperative Range of Motion and Muscle Strength one Year after Shoulder Arthroplasty.

BACKGROUND: Shoulder arthroplasty improves shoulder range of motion (ROM), strength and function in patients with advanced shoulder disease. However, clinical outcomes vary and are not always predictable among patients. Pre-operative factors and patients' characteristics may influence improvement after surgery. This study examined the impact of the pre-operative objective measures range of motion (ROM) and strength, age, sex, and comorbidities on shoulder ROM, strength status and the amount of improvement one year following shoulder arthroplasty. METHODS: 140 patients were assessed pre-operatively and one year after shoulder arthroplasty in this prospective cohort study. Pearson's correlations and multiple regression analyses were performed to test the impact of potential predictors on abduction, flexion, internal rotation and external rotation ROM as well as on shoulder abductors, flexors, internal rotators and external rotators strength at one year. RESULTS: Pre-operative ROM significantly predicted 10% - 37% of the improvement in ROM after surgery. Less pre-operative ROM was associated with a greater improvement in ROM. Less pre-operative muscle strength was associated with a greater improvement in strength after surgery. Pre-operative shoulder muscles predicted 28% - 38% of the strength status at one year, and 24% - 43% of the improvement in strength postoperatively. Older age was associated with less improvement in ROM and strength at one year. With other predictors, age explained 37% of the change in ROM and 36% of the change in strength. Male sex was associated with greater improvement in muscle strength. Sex significantly predicted 24% - 36% of the change in strength. CONCLUSION: Pre-operative ROM and strength, age, and sex are significant predictors of the improvement in the shoulder ROM and strength one year after shoulder arthroplasty. The improvement in these measures is expected to decline with age and men are expected to gain more strength than women following this surgical intervention.