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Submuscular Versus Subcutaneous Ulnar Nerve Transposition: A Cadaveric Study Evaluating Their Utility in Ulnar Nerve Repair at the Elbow
Brandon S. Smetana, MD; Edward W. Jernigan, MD; Wayne A. Rummings Jr, MS; Paul S. Weinhold, PhD; Reid W. Draeger, MD; J. Megan M. Patterson, MD
University of North Carolina, Chapel Hill, NC

Introduction: This study investigated the length gained from subcutaneous and submuscular transposition of the ulnar nerve at the elbow. The information was used to define potential nerve length gains from techniques commonly utilized in attempted primary ulnar neurrohaphy at the elbow.
Materials and Methods: Eleven cadaveric complete upper extremity specimens were utilized. The glenohumeral joints and scapulae were fixed with Steinmann Pins. Standard approach for in situ decompression and mobilization of the ulnar nerve at the elbow was performed. A laceration 2cm distal to the medial epicondyle was created. The nerves were marked 5mm proximal and distal to the laceration site to simulate clinical nerve end preparation during repair. Nerve ends were attached to spring gauges set at 100g of tension (strain <10%) with 5.0 nylon suture (Figure 1). Measurements of nerve overlap were obtained in varying degrees of wrist and elbow flexion using an electronic caliper. Measurements were performed after in situ decompression/mobilization and repeated after both subcutaneous and submuscular transposition. Two and one way RMANOVA analyses were performed to compare overlap means.
Results: Ulnar nerve transposition was found to significantly increase nerve overlap past a threshold of 30 degrees of elbow flexion (Figure 2). No significant difference was seen between subcutaneous and submuscular transpositions at all wrist and elbow positions. Nerve length gained from wrist flexion was significant in all groups independent of elbow flexion and transposition. In situ decompression/mobilization alone with application of 100g tension provided an average of 3.5 cm of maximal length gain, whereas transposition in conjunction with clinically reasonable wrist and elbow flexion (30 and 60 degrees respectively) provided 5.2cm. Controlling for mobilization and with the wrist and elbow placed in clinically acceptable flexion positions a statistically significant increase in overlap of approximately 2cm was gained from transposition.
Conclusions: Subcutaneous and submuscular transposition along with clinically reasonable elbow and wrist flexion afforded a statistically significant length gain of approximately 2cm when compared to in situ decompression/mobilization. However, transposition length gain was only significant at elbow flexion greater than 30 degrees and there was no statistically significant difference between transposition techniques.

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