Design and Validation of a Reaching-Task System for Quantifying Wrist Extension Recovery after Radial Nerve Repair in Nonhuman Primates.

BACKGROUND: Advances in peripheral nerve surgery remain suboptimal, underscoring the need for novel therapies typically tested in small-animal models, where functional assessment, a critical translational endpoint, is inherently limited. Non-human primates (NHPs) bridge this gap but lack standardized quantitative functional assessments. Here, we aimed to design and validate a standardized, reproducible, and quantitative reaching-task system for measuring maximum active wrist extension in NHPs, and to demonstrate its applicability for the longitudinal assessment of motor recovery following radial nerve repair. New method A custom-built reaching-task system was developed to isolate wrist extension in NHPs while minimizing upper-limb compensation. A standardized dual-camera configuration enabled frame-by-frame kinematic analysis via motion-tracking software. Reliability was tested in two healthy NHPs across three repeated sessions, and a proof-of-concept experiment assessed recovery in an NHP following nerve repair. RESULTS: Maximum wrist extension angles showed high inter- and intra-subject reliability (ICC > 0.90), with a significant relationship between target height and extension angle (β = 3.92°, R² = 0.77). In the nerve repair model, maximum wrist extension improved from 20.1 ± 7.7° at 103 days post-repair to 39.5 ± 6.9° at 180 days (p < 0.001), consistent with electrophysiological evidence of reinnervation; kinematic profiles revealed gradual restoration of function. Comparison with existing methods This system standardizes limb positioning and target placement, enabling synchronized kinematics for consistent extraction of wrist angles. CONCLUSIONS: This reaching-task system provides a standardized, quantitative assessment of wrist extension after radial nerve repair, supporting its translational relevance as a platform for preclinical therapeutic evaluation.