Purpose Instability and fractures may result from tensioning errors during reverse total shoulder arthroplasty (RTSA). To help understand tension, we measured intraoperative glenohumeral contact forces (GHCF) during RTSA. Methods Twenty-six patients underwent RTSA, and a strain gauge was attached to a baseplate, along with a trial glenosphere. GHCF were measured in passive neutral, flexion, abduction, scaption, and external rotation (ER). Five patients were excluded due to wire issues. The average age was 70 (range, 54–84), the average height was 169.5 cm (range, 154.9–182.9), and the average weight was 82.7 kg (range, 45.4–129.3). There were 11 females and 10 males, and thirteen 42 mm and 8 38 mm glenospheres. Results The mean GHCF values were 135 N at neutral, 123 N at ER, 165 N in flexion, 110 N in scaption, and 205 N in abduction. The mean force at terminal abduction is significantly greater than at terminal ER and scaption (p < 0.05). Conclusions These findings could help reduce inappropriate tensioning.

Although soft tissue tension is an important factor in the clinical performance of reverse total shoulder arthroplasty (RTSA), this tension has not been quantified intraoperatively. Knowledge of the shoulder joint reaction forces during RTSA could facilitate the optimal placement of implant components to minimize the risk of both intra-and postoperative complications. We developed a strain gauge instrumented trial glenosphere to measure shoulder joint reaction forces during RTSA. The strain gauges and their connections were hermetically sealed against body fluids by biocompatible materials. All materials in direct body contact were biocompatible. In this study, we introduce the structure and calibration results of the instrumented prosthesis. We also demonstrate the practical use of the prosthesis on a cadaveric shoulder. The instrumented prosthesis showed mean measurement errors of approximately 3.4% for forces up to 400 N. A maximum joint reaction force of 132 N was observed during abduction in a single cadaver specimen. This sensor will be useful for quantifying soft tissue tension during RTSA surgery.