Using a Reaching Task Model for Hand Functional Assessment in Non-Human Primates Following Radial Nerve Surgical Repair

Introduction: Several methodologies exist to evaluate hand grip function in non-human primate (NHP) models, primarily focusing on grip strength and flexor muscle integrity. Hand grip requires coordinated input from both extrinsic and intrinsic muscles, involving the median and ulnar nerves. In contrast, wrist, thumb, and metacarpophalangeal (MCP) joint extension depend solely on the radial nerve and are easier to assess without impairing the primates' feeding or self-care abilities. Therefore, we prefer the radial nerve injury model to evaluate hand function in NHPs after radial nerve reconnection.

Methods: We designed a reaching task utilizing a custom-built system, incorporating a box attached to the primate's cage. This system allows video recording from two perspectives (side and top view) to analyze the primate's reaching behavior for food, thereby assessing the functionality of its wrist and hand following radial nerve reconstruction. The system features an adjustable shelf that can be positioned at various heights (0 – 5 cm), compelling the NHP to extend the wrist upward depending on the height, allowing for the assessment of wrist and MCP joint extension.

Results: This methodology allows for the measurement of extension angles in the wrist, and evaluate MCP joint, and thumb function during the reaching task. The data can be analyzed using a scoring system based on distinct thresholds, enabling comparisons of functional outcomes between limbs and facilitating the evaluation of new therapeutic interventions in peripheral nerve surgery.

Conclusion : The proposed reaching task and grading system provide a valuable framework for assessing functional recovery in NHP models after radial nerve injury, offering insights into the efficacy of novel therapeutic strategies for peripheral nerve repair and their potential translation to patient management.