The evolution of nerve transfers for spinal cord injury

Spinal cord injury (SCI) often results in devastating effects on function and quality of life. The majority of SCIs occur in the cervical region with restoration of arm and hand function being the highest priority by patients. Current restoration strategies rely on maximizing and optimally redistributing residual muscle functions that remain under volitional control. The polio epidemic and World Wars led to the development and refinement of tendon transfers, which has long been the standard reconstructive approach for the upper extremity following SCI. However, the past few decades has seen the emergence of nerve transfers from a "salvage" procedure for the management of peripheral nerve injuries, to a powerful reconstructive tool following SCI. Nerve transfers offer distinct advantages over tendon transfers; however, optimal functional recovery frequently benefits from a multi-modality approach and must be tailored to specific injury patterns. Extension of nerve transfers to the lower body presents additional hurdles such as limited donor nerve sources and much longer target distances. In this review, we will discuss the evolution of nerve transfers for upper extremity reanimation following cervical SCI and discuss advantages over tendon transfers. We will address the progress for nerve transfers to restore lower body function, including ambulation and bladder control. Finally, we will address future efforts in the field. Reconstructive modalities, including nerve and tendon transfers, remain underutilized following SCI and it is important that these therapeutic options are made known to the research community, medical providers, and patients.