Brachial plexus injuries are major cause of severely debilitating upper extremity impairment. In these cases, the restoration of elbow flexion is a primary goal. Nerve transfers have emerged as the preferred reconstructive option in cases where direct nerve repair or grafting is either impossible or unfavorable.1,2 Several donor nerves have been described, including ulnar nerve motor fascicles, median motor fascicles, intercostal, medial pectoral, spinal accessory, and phrenic nerves.3–5 Transfer of the thoracodorsal nerve has also been described.6 There exists little objective data, however, regarding the functional morbidity following latissimus dorsi denervation, although several studies have shown that latissimus harvest results in some level upper extremity functional morbidity.7 Furthermore, harvest of the entire nerve eliminates it as a donor in the setting of elbow flexion transfer failure. Anatomic studies have shown that a bifurcation of the latissimus neurovascular supply exists before its entry into the muscle in nearly all patients.8 Raksakulkiat et al.10 described transfer of the lateral branch of the thoracodorsal nerve, or LaT branch, for reinnervation of the long thoracic nerve. This report describes transfer of the LaT branch as an effective and reliable option for biceps reinnervation with minimal postoperative morbidity.
Our patient is a 45-year-old man who sustained a self-inflicted gunshot wound to the right chest. He presented 6 months after injury with a patchy but global brachial plexus deficit, including a manual muscle testing (MMT) grade of 0/5 for elbow flexion. Electromyography (EMG) showed partial or complete injury to the median, ulnar, radial, musculocutaneous, axillary, and lateral pectoral nerves. Therefore, the preoperative plan was to transfer the thoracodorsal nerve proper, which was electro-diagnostically intact, to the biceps branch of musculocutaneous nerve. In the operating room with the patient supine, an incision was made along the medial aspect of the upper arm to expose the musculocutaneous nerve and its biceps branch. Once these were isolated, the incision was extended through the axilla and onto the upper lateral chest to expose the thoracodorsal nerve. After the bifurcation was identified, the LaT branch appeared to be of similar size to the biceps branch (see figure, Supplemental Digital Content 1, which displays photos of the surgical procedure showing (A) exposure, (B) isolation of the biceps branch (yellow loop) and LaT branch (blue vessel loop), (C) transfer of the LaT branch to the biceps branch, and (D) coaptation, https://links.lww.com/PRSGO/A684). At that point, it was decided to transfer only the LaT branch to preserve some latissimus function. Internal neurolysis of the LaT branch was performed to gain adequate length, and neurorrhaphy was performed utilizing 8-0 nylon suture. The patient was placed in a long arm splint and stayed 1 night in the hospital. He was seen at 2, 4, and 12 months and underwent electrodiagnostic testing at 2 and 11 months.
Four cadaver torsos were obtained from the University of Pittsburgh School of Medicine. Dissection was performed on 8 upper extremities to identify the thoracodorsal nerve and its bifurcation and identify the location of the bifurcation with respect to its distance from the latissimus dorsi insertion on the humerus. Segments of the LaT branch, biceps branch, thoracodorsal nerve, and musculocutaneous nerve were sent to pathology for histology and stained with luxol fast blue. Photographs of the sections were taken using a Nikon 90i (Melville, NY) microscope camera and axon counts for each nerve were made using image J (National Institutes of Health, Bethesda, MD).
Our patient had no complications. Electro-diagnostics of the right latissimus dorsi at 2 months did not demonstrate any abnormality on EMG testing, consistent with preoperative findings. Not unexpectedly, there were no new signals noted in the biceps muscle at this time. At 4 months, our patient had progressed to MMT grade of 1/5 for elbow flexion, with visible firing of his biceps tendon when asked to actively flex the elbow. By 11 months, the electro-diagnostics demonstrated improvement in biceps, with recruitment of 20% of the motor unit pool compared with the contralateral side, a significant increase from previous EMG. Readings of the right latissimus remained normal. Furthermore, our patient had progressed to an MMT grade of 4/5 with dramatic increase in visible contraction of the biceps (Fig. 1). Overall, the patient was extremely satisfied with the results of the transfer.
The thoracodorsal nerve bifurcated before entering the muscle in all specimens, and the LaT branch was transferrable to the biceps branch in all cases with only limited internal neurolysis (Fig. 2). On average, the thoracodorsal nerve bifurcation was located 7.5 cm ± 1.18 cm (range, 6.2–9.6 cm) inferior to the latissimus insertion on humerus. Axon counts revealed that, on average, the LaT branch contained 1,453 ± 289 axons, the biceps branch contained 1,715 ± 699 axons, the thoracodorsal nerve contained 2,789 ± 707 axons, and the musculocutaneous nerve contained 6,784 ± 2,545 axons. The resulting donor-to-recipient axon count ratio for the LaT branch to biceps branch is 0.85:1.
This is the first report of transfer of the LaT branch for the restoration of elbow flexion. The patient in this case showed significant improvement in elbow flexion at 11 months, and the results of our cadaver dissection revealed similar axon counts to previous reports, yielding a favorable donor-to-recipient nerve axon count ratio of 0.85:1.10 Schreiber et al.9 recently published a study analyzing the various options for biceps reinnervation, looking specifically at the axon counts of the respective nerves compared with that of the biceps branch.9 After correlating clinical outcomes to donor-to-recipient nerve axon count ratio, the authors concluded that a ratio greater than 0.7:1 was necessary to achieve a successful outcome. The LaT branch to biceps branch ratio from our study falls well into this range.
In cases of severe trauma, donor nerve options are limited. Additionally, when considering nerves for transfer, thought should be given to preserving as much residual function as possible. The case and cadaver dissection presented in our study demonstrates the efficacy and feasibility of the LaT branch for use in reinnervation of the biceps brachii muscle. The nerve is present in a reliable location and can easily swing over to the biceps branch of the musculocutaneous with minimal internal neurolysis, if necessary. It also spares the medial branch of the thoracodorsal, resulting in no obvious functional postoperative morbidity. We hypothesize that when the LaT branch is available, it provides a low morbidity option for biceps reinnervation. Studies with a larger cohort and longer follow-up are needed to better understand the potential and limits of this procedure.
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