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Does Pre-Operative Donor Nerve Electromyography Predict Nerve Transfer Outcomes?
Joseph J. Schreiber, MD, Joseph H. Feinberg, David J. Byun, Steve K. Lee and Scott W. Wolfe
Orthopaedic Surgery, Hospital for Special Surgery, New York, NY
Introduction: Brachial plexus injuries are debilitating, with nerve transfer surgery playing an integral role in reconstruction[1-2]. Several factors have been identified that may predict success of nerve transfers, including patient age, injury to surgery duration, BMI, and the number of active motor neurons in the donor fascicle. Electromyography (EMG) is routinely used pre-operatively to estimate the degree of muscle denervation and motor unit preservation[3]. However, its ability to predict post-operative motor outcome has not been evaluated. We hypothesized that health of the donor nerve, as assessed by EMG, could predict the success of nerve transfers. Materials and Methods: A retrospective review of our nerve registry was performed to investigate outcomes of two common transfers: 1)ulnar or median nerve fascicular branch transfer to the biceps or brachialis motor branches, or 2)long or medial head triceps branch transfer to the axillary nerve. Motor strength was graded pre-operatively and after a minimum one-year follow-up. Pre-operative EMG results were classified as functionally normal or abnormal based on motor recruitment pattern. Abnormal spontaneous activity and recruitment intervals were also evaluated. Mann-Whitney U test was used to compare differences in follow-up motor strength improvement. Results: A total of 40 nerve transfers were identified; 27 performed for elbow flexion and 13 for shoulder abduction. Twenty-nine functionally normal donor nerves and 11 abnormal donor nerves were identified. Mean motor strength increased from 0.2 pre-operatively to 4.1 post-operatively in the functionally normal EMG cohort, as compared to 0.0 to 3.0 in the abnormal EMG cohort (P=0.01). Overall, 22 of 27 patients (81%) recovered elbow flexion strength of M4 or higher, and 10 of 13 (77%) recovered deltoid strength of M3 or greater. There were no demographic differences identified. Discussion: Our findings suggest that when planning nerve transfers for brachial plexus reconstruction, EMG evaluation of the quality of potential donor nerves can serve to prognosticate post-operative motor strength outcomes. Our improvements in elbow flexion and shoulder abduction are comparable to historical results[1-2]. Despite the small numbers studied, we observed significantly greater gains in motor strength in the functionally normal donor nerve cohort as compared to the abnormal donor nerve cohort. Pre-operative EMG evaluation should be considered an integral component of the donor nerve selection process when planning brachial plexus reconstruction. References: 1. Mackinnon et al, J Hand Surg 2005;30(5):978-985. 2. Leechavengvongs et al, J Hand Surg 2003;28(4):633-638. 3. O'Shea et al, Eur J Hand Surg. 2011;36(9):747-759.
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