Treatment Effects of Reverse Total Shoulder Arthroplasty for Unilateral Cuff Tear Arthropathy – Outcomes at 6, 12, 24 and 60 Months and Confounders

Abstract Background Although shoulder arthroplasty is less common than knee or hip arthroplasty, the number of procedures being performed is increasing rapidly. The treatment effect is a simple method to measure outcome of joint replacement for each patient individually. The method was applied to measure outcome of total hip/knee arthroplasty but not yet for shoulder arthroplasty. Methods The patients with reversed total shoulder arthroplasty (RSA) of five European clinics were included in this prospective study. The treatment effects (TE) were calculated for each patient as complaint reduction/baseline complaints. 1 is the maximal treatment effect and corresponds to a patient without complaints. A positive number means amelioration, 0 = unchanged, a negative number means worse. The primary aim was to calculate the TE’s for RSA at 6, 12, 24, and 60 months postoperatively. The secondary aim was to analyze the influence of confounders (preoperative grade of cuff tear arthropathy, age, gender, dominance, side of the affected shoulder, general co-morbidities measured using ASA grade). Results 203 patients were included for this analysis of whom 183 patients had a complete 2 year follow up. Over the 24-months, the mean ASES score augmented significant from 20.5 to 78.7 (p<0.001). The 2 year treatment effects ranged from 1 to 0.09. We had no patient with a negative TE. A higher Hamada grade was associated with better TE’s (Hamada grade 4+ vs. 2, p-value 0.042). For age and dominant side there were weak associations where those aged 80+ and dominant side had better TE’s. The patients with higher ASA grade had lower TE’s (ASA grade 4+ vs. 1, p-value 0.013). The mean TE’s were 0.77 at 6-months, 0.81 12-months, 0.76 24-months and 0.73 at 60-months. Conclusions The treatment effects for reverse shoulder arthroplasty vary from 1 to 0.09. The treatment effects change little in the first five postoperative years (from 0.73 to 0.81). The confounders for better TE’s were: higher severity of cuff arthropathy (Hamada grade 3, 4 and 5), less co-morbidities (ASA Grade 1), higher age (80+) and dominant side. Gender did not influence the 2-year TE’s.