The survey presented 2 case scenarios (sharp ulnar nerve injury either 9 cm proximal or 9 cm distal to the elbow) and respondents selected the operative procedures that would be considered, including nerve repair, transposition, autograft, allograft, and nerve transfer (end-to-end or end-to-side AIN to ulnar motor). For proximal elbow injury, 74% would consider nerve repair, 46% transposition, or 40% autograft; 57% would perform distal end-to-end nerve transfer; and 13% would allograft. For distal elbow injury, 79%, would consider nerve repair, 42%, autograft, or 31% transposition; 35% would perform distal end-to-side nerve transfer and 29% would perform an end-to-end nerve transfer; and 14% would allograft. There were significantly more surgeons using distal end-to-end nerve transfer for proximal injury than distal injury with end-to-side nerve transfer (χ2 = 63.48, P < 0.001).
The rise in publications regarding nerve transfers since the early 1990s has continued and parallels the reintroduction of nerve transfers as an alternative reconstruction. Following the early descriptions of successful nerve transfer for restoration of ulnar and musculocutaneous nerve function, an increasing number of unique nerve transfers and clinical outcomes have been described. Novel donor-recipient combinations, modified techniques of coaptation, including end-to-side, and sensory nerve transfers continue to evolve as surgeons seek solutions to difficult reconstructive challenges. Each new technique stimulates discussion, and comparisons to alternative reconstructive methods, to determine optimal management of nerve injuries.
Our surgeon survey and literature review provide insight into the change in surgical practice and increased use of nerve transfers. Outcome studies and reviews have compared results after nerve graft and nerve transfers and the conclusions vary depending on multiple factors (injury, patient, and surgical), including injury location (proximal brachial plexus versus distal nerves), specific function to be restored, and nerve transfer technique. Although studies frequently report data trends, many studies lack statistical power due to small samples, and seemingly large differences between outcomes fail to reach statistical significance. In our review, we included results that were statistically significant as the criterion for outcome differences. Therefore, in some cases our interpretation of the findings differed from authors’ conclusions, where authors discussed their results based on apparent statistical trends. In Tables 2 and 3, we have included detailed findings (often presented as a percentage reaching a threshold strength) and those trends failing to reach significance can still be appreciated.
Overall, the literature supports roles for both nerve transfer and graft reconstruction for upper extremity peripheral nerve lesions, although their relative utilities are best examined for different functions individually.
Shoulder function occurs via the coordinated actions of multiple musculoskeletal structures from the scapula and glenohumeral joint. Functional shoulder restoration following nerve injury has been difficult, and nerve transfers and grafts can generate useful shoulder motion.12–14,19 The SSN and axillary nerve are the predominant targets for muscle reinnervation. With isolated axillary nerve injuries and normal SSN function, overall postoperative results of the shoulder seem roughly equivalent following both nerve transfer and nerve graft techniques. With brachial plexus injuries, functional impairment is more severe and surgical results depend on reconstructed nerves.19 The SSN function is essential for overall shoulder function and traditional nerve graft reconstruction from C5 and C6 roots or the upper trunk has yielded only fair results. Nerve transfers utilizing the spinal accessory nerve to the SSN have not proven superior. This may be in part due to the importance of the scapular motion associated with the spinal accessory nerve and it is not “particularly” expendable. Efforts have been made to preserve function by performing an end-to-side transfer with crush injury via an anterior approach,20 and more distal end-to-end transfers via posterior approaches.21,22 No study has reported improved results for SSN nerve transfer compared to graft. Similarly, nerve transfers to the axillary nerve alone have not produced superior function compared to nerve grafting. As with SSN reconstruction, nerve transfer techniques are not standardized. The axillary nerve transfer is performed typically using a triceps branch of the radial nerve but variation has been reported in the recipient axillary nerve branch being reinnervated and the selected donor triceps branch. These specific technical differences may affect outcomes, although the extent of that impact remains unknown.
Whereas nerve transfer for isolated SSN or axillary nerve injuries has not improved results, simultaneous transfers have resulted in superior outcomes and are highlighted in the systematic review by Yang et al. of separate graft and transfer studies.9 When performed in combination, the restoration of SSN and axillary nerve function is superior following nerve transfer. Although the majority of studies assessing dual transfers utilized the spinal accessory nerve and a triceps branch of the radial nerve, there was variation in the specific details regarding the donors, recipients, and surgical approaches. The relative utility of grafts and transfers remains unclear if one of the preferred donors is unavailable (such as C5–C7 injuries).
Elbow flexion reconstruction is less challenging than shoulder function, with superior results following both nerve graft and transfer. Although the literature supports the use of either single or double fascicular nerve transfer compared to nerve graft, variation in surgical technique impacts functional recovery and donor deficits.18 The advantages of these 2 nerve transfer techniques compared to nerve graft would be moderated with a more distal injury (such as at the lateral cord level or isolated musculocutaneous nerve) due to the similar reinnervation distances.
Nerve transfers for restoration of triceps function, accessory nerve injuries, hand function in lower brachial plexus injuries, and C7 tetraplegia patients have been reported in small sample studies.23,24 The results following these nerve transfers are encouraging but there are no comparison studies between techniques.
With increasing distance between the nerve injury and target muscle, the time duration to muscle reinnervation increases. To minimize the time for neural regeneration, distal AIN transfers to reinnervate the ulnar intrinsic muscles were performed.25 Direct comparisons between ulnar nerve transfer and graft reconstructions have been performed. Generally, nerve transfers have been considered superior to nerve grafting for neurotmetic ulnar nerve injuries in the arm.15 This transfer has been reported using an end-to-side coaptation (supercharge technique) to supplement recovering axonotmetic injuries or repaired neurotmetic injuries in the proximal forearm26 or more proximal ulnar nerve injuries in patients with a Martin-Gruber anastomosis. The relative utility of this technique has been clinically reported.16
Radial and median nerve transfers are more recent developments, and there are no clinical studies directly comparing nerve graft and transfers. For radial nerve injuries, the debate continues over the use of nerve transfers versus tendon transfers.27 Tendon transfers have been used reliably for functional restoration when nerve graft or repair fails or is not feasible. Whereas tendon transfers provide rapid, consistent recovery, nerve transfers offer the opportunity for independent finger movement. Our nerve transfer results have been driven by modification of surgical technique, postoperative motor reeducation, and most importantly, appropriate patient selection. With different advantages and indications, the selection of tendon or nerve transfer remains patient-specific depending on individual needs. Similar to radial nerve palsy, distal median nerve lesions are often amenable to tendon transfer. However, nerve transfers have facilitated recovery of pronation and is effective for these otherwise challenging injuries. No comparative median nerve studies between nerve transfer and graft or tendon transfer were identified.
Innovation, Paradigm Shift, and Nerve Transfer
Changes in practice to manage patients with nerve injury are inevitable. Surgical innovation is initiated by pioneers, frequently from preeminent departments of surgery, who spend their careers developing, promoting, and teaching their techniques (eminence-based surgery). Each innovation has strong advocates and supporters and new paradigms are met with confrontation, criticism, skepticism, and anger. Thomas S. Kuhn identified a paradigm shift as a fundamental change in the practice of a scientific discipline, described as a scientific revolution.28 Kuhn emphasized that “failure of existing rules is the prelude to a scientific search for new ones and when enough information has accrued against a current paradigm, the scientific discipline is thrown into a state of crisis, and a new paradigm forms with new followers; frequently with an intellectual battle between the new paradigm supporters and old paradigm holdouts.” Kuhn outlines the challenge of transferring allegiance between paradigms and notes that resistance is inevitable.28 Kuhn continues, “Still, to say that resistance is inevitable and legitimate, that paradigm change cannot be justified by proof, is not to say that no arguments are relevant or that scientists cannot be persuaded to change their minds. Though a generation is sometimes required to effect the change, scientific communities over time have been converted to new paradigms.”
Many surgical options exist on the reconstructive ladder for functional restoration following nerve injuries and depending on the nerve, results may be maximized by different techniques. The literature suggests that for most nerve lesions, nerve transfers are at least equivalent to grafts, and, in some cases, generate superior results. Nerve transfer eliminates the major issues associated with poor clinical results (proximal injuries with long target end-organ distances, delayed repair, sensorimotor topographical mismatching, nerve repair tension, or for nerve graft 2 coaptation sites and cellular changes in long grafts that inhibit nerve regeneration).6 The reconstruction approach requires a comprehensive preoperative and intraoperative assessment and consideration of patient and injury factors.29 Selection of the reconstruction should include consideration of the immediate functional needs, potential future reconstruction and a combination of different surgical options may be optimal. We acknowledge the low response rate with the surgeon survey and this is not unique for a physician survey. Low response rates have the potential for response bias and previous studies have evaluated methods to increase survey response.30 Because surgeons represent a relatively homogeneous sample, the sample in this study is likely representative of the population sampled. Therefore, the results from the surgeon survey can be generalized to the current practice and management of nerve injuries.
Optimal outcome following nerve injury may involve a combination of different surgical options and more than one type of reconstruction. Nerve transfer is a logical extension of the paradigm shift from nerve repair and nerve graft and offers a new rung on the reconstruction ladder.
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