American Society for Peripheral Nerve

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Evaluation for Late Nerve Transfer Surgery: Predicting the Degree of Lower Motor Neuron Injury in SCI
Nirbhay S. Jain, BS1; Elspeth Hill, MD2; Dan A. Hunter, RA2; Craig Zaidman, MD3; Carie Kennedy, BS4; Christine B. Novak, PT, PhD5; Neringa Juknis, MD6; Rimma Ruvinskaya, MD4; Susan E. Mackinnon, MD1; Ida K. Fox, MD1
1Department of Surgery, Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, St. Louis, MO, 2Department of Surgery, Division of Plastic and Reconstructive Surgery, Washington University School of Medicine, St Louis, MO, 3Washington University in St. Louis, Department of Neurology, St. Louis, MO, 4Washington University in St. Louis, St Louis, MO, 5Hand & Upper Extremity Program, Division of Plastic & Reconstructive Surgery, University of Toronto, Toronto, ON, Canada, 6Washington University in St. Louis, St. Louis, MO

Nerve transfer surgery (NT) is being used to restore upper extremity function in the setting of cervical spinal cord injury (SCI) with substaintial variation in clinical outcomes. One factor that may contribute is the possibility of mixed upper motor neuron (UMN) and lower motor neuron (LMN) injury patterns. In isolated UMN injury, a satisfactory result could be obtained years post-SCI. This work correlates the results of preoperative electrodiagnostic testing (EDX) with intraoperative neuromuscular stimulation (NMS) to define the extent of LMN injury present, and establishes the histopathologic basis for these findings.

Materials and Methods
We reviewed records of people who had supinator to posterior interosseous nerve (PIN) and brachialis to anterior interosseous nerve (AIN) and/or branches to flexor digitorum superficialis (FDS) NT and collected data on: 1) intraoperative NMS, 2) preoperative EDX, and 3) nerve histopathology. NMS was catagorized as absent or present for both donor and recipient nerves. Both nerve conduction study (NCS) and electromyography (EMG) of corresponding musculature were reviewed for evidence of LMN involvement. Tissue specimens were examined for normal, abnormal, and mixed patterns of nerve fiber histomorphometry.

We found data available for 56 discrete donor and 52 discrete recipient nerves over 40 surgeries and 20 patients. This included a population presenting both <1 year and over a decade post-SCI. The intraoperative presence of recipient NMS corresponded to preoperative studies with normal recipient NCS, the absence of denervation on EMG, and normal nerve architecture. Conversely, the absence of recipient NMS corresponded to abnormal preoperative motor NCS and denervation on EMG. However, the sensory NCS were normal, suggesting isolated cord level injury to the ventral horn with preservation of the dorsal root ganglion. This injury pattern was reflected in a mixed pattern with loss of large caliber motor fibers and normal-appearing small sensory fibers on histomophometric exam of the recipient nerve tissue.

This study supports the idea that differing patterns of UMN and UMN/LMN injury patterns exist in SCI. By using preoperative EDX, individuals with these patterns of injury can be appropriately counseled on their eligibility for these surgeries.

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