Animal Models for Selective Nerve Transfers of the upper Extremity

Introduction Nerve transfers are an important tool to restore muscle function. Despite their popularity in reconstructive surgery, their effects on the motor unit remain largely unknown. Therefore, a realistic animal model is needed for the upper extremity, which is where the majority of nerve transfers are conducted. This work shows different upper extremity nerve transfer models in the rat, where elbow flexion was restored with different types of nerve transfer in adult and neonatal rats. Methods Anatomy and microsurgical feasibility was first evaluated in 10 adult and 5 neonate Sprague Dawley rats. In 40 rats (30 adult and 10 neonate), a nerve transfer of the whole ulnar nerve or just the deep branch was performed to reinnervate the long head of the biceps muscle. After 12 weeks of regeneration, the transfer was evaluated for functional aspects such as muscle force and weight. Results Neural anatomy was constant in all rats. All nerve transfers were successful and functional analyses showed a maximum tetanic muscle force of 2.47 + 0.25 N after an ulnar nerve transfer. Deep branch transfers achieved 1.96 + 0.65 N, and neonates achieved 1.1 + 0.23 N. Control side was 2.78 + 0.24 N. The muscle weight was 325.6 + 0.24 mg for the control, 313.8 + 0.25 mg after UN transfer, 226.7 + 0.65 mg after deep branch transfer and 85.5 + 0.23 mg for neonates. Discussion For proper clinical translation, an upper extremity model is needed. Successful reinnervation in all groups was demonstrated, which indicates an excellent model for future research. Variations in functional parameters are likely the effect of different donor axon ratios. Neuronal plasticity also appears to play a major role in the regeneration potential. Conclusion: This work illustrates several animal models to further investigate nerve transfers on all levels of the motor unit.