Force‐amplifying implant to improve key pinch strength in tendon transfer surgery: Cadaver model proof‐of‐concept

The brachioradialis (BR) to flexor pollicis longus (FPL) tendon transfer surgery is a common procedure used to restore key pinch grip for incomplete spinal cord injury patients. However, the procedure only restores 22% of the physiological grip strength, which is important for successfully grasping objects and minimizing fatigue. The purpose of this study was to evaluate the efficacy of using a novel force‐amplifying pulley implant to modify the standard BR to FPL tendon transfer surgery to improve key pinch grip strength in a human cadaver forearm model. A total of eight cadaveric specimens were mounted onto a custom testbed where a torque‐controlled motor actuated the BR tendon to produce key pinch grip. In each cadaver, two experimental groups were examined: a standard and an implant‐modified BR to FPL tendon transfer surgery. A force sensor mounted to the thumb recorded isometric key pinch grip forces over a range of input BR forces (2 N–25 N) applied in a ramp‐and‐hold protocol. Across the range of input BR forces, the average improvement in key pinch grip strength in the implant‐modified surgery compared to the standard surgery was 58 ± 7.1% (ranging from 41% to 64% improvement). Throughout the experiments, we observed that the implant did not hinder the movement of the BR or FPL tendons. These results suggest that a BR to FPL tendon transfer surgery utilizing a force‐amplifying pulley implant to augment force transmission can provide additional functional strength restoration over the standard procedure that directly sutures two tendons together.