Relationship between the preoperative grip strength and postoperative shoulder strength of patients treated via reverse shoulder arthroplasty

Background Systemic disorders including diabetes mellitus, obesity, and depression affect the outcomes of reverse shoulder arthroplasty (RSA). Sarcopenia (a general skeletal muscle disorder) is common in elderly people, but its effect on patients after RSA is not clear. We hypothesized that the preoperative sarcopenia indices of grip strength and general skeletal muscle mass would correlate with the clinical outcomes of RSA Methods Grip strength and general skeletal muscle mass were measured in patients scheduled (between 2016 and 2021) for primary RSA to treat cuff tear arthropathy, an unrepairable cuff tear, or osteoarthritis with a large cuff tear. Before surgery, grip strength was measured using a hydraulic dynamometer and general skeletal muscle mass was calculated from the appendicular relative skeletal muscle mass index (aRSMI) using dual-energy X-ray absorptiometry. In all, 58 patients were included; the minimal follow-up duration was 12 months. The postoperative clinical results (pain, active range of motion, shoulder strength, and functional scores) were evaluated during scheduled outpatient visits. We calculated correlations between the preoperative sarcopenia indices, and the clinical results at the final follow-up. Results The mean preoperative grip strength and aRSMI were 21.6 ± 4.0 kg and 5.98 ± 0.84 kg/m2 in females, and 30.6 ± 7.5 kg and 7.21 ± 0.94 kg/m2 in males, respectively; the grip strength and aRSMI were not associated with each other (P = 0.083). Ten females (25%) and 10 males (56%) met the criteria for sarcopenia. The postoperative abduction shoulder strength and Constant–Murley shoulder score increased significantly with higher preoperative grip strength (R = 0.420 and P = 0.001; and R = 0.497 and P < 0.001, respectively) and the American Shoulder and Elbow Surgeons Score was related to the preoperative aRSMI (R = 0.320, P = 0.039). Conclusions The shoulder strength and functional score after RSA correlated positively with the preoperative grip strength. Measuring grip strength before RSA allows the surgeon to predict shoulder strength after RSA.