Refinements of nerve repair with connector-assisted coaptation.

Peripheral nerve repair can be very rewarding for both surgeon and patient when expected outcomes are achieved. In many cases, however, the results are suboptimal due to number of possible objective and technical reasons. Although we cannot influence patent's comorbidities, the extent or mechanism of the nerve injury, we may help optimize technical details when aiming towards improved outcomes. While the suture coaptation for primary nerve repair or nerve reconstruction with grafting served as the reconstructive standard for many decades, technical imperfections remain threats to reconstructive goals. Tension, fascicular misalignment generated by over tightening suture coaptation, deeply placed sutures, reactive scarring to foreign material at anastomosis site, may all negatively affect axonal regeneration. As the goal of every nerve repair is to have ideally opposed tension free nerve fascicles, protected from the deleterious effects of the wound bed. The utilization of coaptation aids to overcome the challenges of nerve repair has been suggested as an alternative to the classical suture repair. A review of clinical literature was performed to assess the evidence for this technique and the critical success factors to consider when implementing this technique. Twelve clinical studies met criteria, majority suggesting improved outcomes by the utilization of a coaptation aid. Most commonly reported improvements were improved sensory outcomes, reduced tenderness or pain at the coaptation site and reduced operative time. The current clinical evidence data suggests that utilization of a coaptation aid is a technical innovation to help provide better nerve repair and reconstructive functional outcomes.

Surgery and Behavioral Testing in the Tibial Neuroma Transposition Model in Rats.

The tibial neuroma transposition (TNT) is a rat model in which allodynia at the neuroma site (tibial nerve) can be independently evaluated from allodynia at the plantar surface of the hind paw innervated by the intact sural nerve. This TNT model is suitable to test therapies for neuroma pain, such as the potential superiority of certain surgical therapies that are already used in the clinic, or to evaluate new drugs and their effect on both pain modalities in the same animal. In this model, a distal lesion (neurotmesis) is made in the tibial nerve, and the proximal nerve end is transposed and fixed subcutaneously and pretibially to enable assessments of the neuroma site with a 15 g Von Frey monofilament. To assess allodynia over the sural nerve, Von Frey monofilaments can be used via the up-down method on the plantar lateral region of the hind paw. After cutting the tibial nerve, mechanical hypersensitivity develops at the neuroma site within 1 week after surgery and persists at least until 12 weeks after surgery. Allodynia at the sural innervated plantar surface develops within 3 weeks after surgery compared to the contralateral limb. At 12 weeks, a neuroma forms on the proximal end of the severed tibial nerve, indicated by dispersion and swirling of axons. For the TNT model surgery, multiple critical (micro)surgical steps need to be followed, and some surgery practice under terminal anesthesia is advised. Compared to other neuropathic pain models, such as the spared nerve injury model, allodynia over the neuroma site can be independently tested from sural nerve hypersensitivity in the TNT model. However, the neuroma site can be tested only in rats, not in mice. The tips and directions provided in this protocol can help research groups working on pain successfully implement the TNT model in their facility.

Surgical Treatment Strategies for Injuries of the "Unforgiving" Superficial Branch of the Radial Nerve.

BACKGROUND: Neuropathic pain caused by adhesions or neuroma formation of the superficial branch of the radial nerve (SBRN) is difficult to treat. The authors evaluated the effectiveness of different routinely used surgical techniques for SBRN neuralgia to provide a basis for future studies on SBRN neuralgia and explored the prognostic value of a preoperative diagnostic nerve block. METHODS: The authors performed a retrospective cohort study by reviewing surgical records for procedures to treat SBRN neuralgia. Patient satisfaction was scored as satisfied or unsatisfied, and pain intensity was scored with a numeric rating scale. RESULTS: The authors included 71 patients who had 105 surgeries on the SBRN. Patients with a neuroma ( n = 43) were most satisfied after proximal denervation with burying into the brachioradialis muscle compared with burying elsewhere (53 versus 0 percent; p < 0.001). Adhesions of the SBRN ( n = 28) were treated with neurolysis (39 percent satisfied). If neurolysis or denervation did not suffice, an additional denervation of the lateral antebrachial cutaneous nerve or posterior interosseous nerve led to satisfaction in 38 percent. A decrease of less than 3.5 points on the numeric rating scale score after diagnostic nerve block led to higher postoperative pain scores (4.0 versus 7.5; p = 0.014). The authors found that the outcome of the diagnostic nerve block can predict the outcome of SBRN denervation and burying into brachioradialis muscle. CONCLUSIONS: The most effective burying technique is burying the SBRN into the brachioradialis muscle. Future studies on the treatment of SBRN neuralgia should therefore compare newer techniques, with burying the SBRN into the brachioradialis muscle as the control group.

Application of a Porcine Small Intestine Submucosa Nerve Cap for Prevention of Neuromas and Associated Pain.

Painful neuroma formation is a common and debilitating sequela of traumatic or oncologic nerve amputations. Studies suggest that isolating transected nerve stumps within protective caps during amputation surgery or revision procedures may assist in preventing symptomatic nerve-end neuroma formation. This study evaluated the local effects of two porcine small intestine submucosa (pSIS) nerve caps of differing configurations on a terminal nerve end in an animal model. The tibial nerves of 57 Sprague Dawley rats were transected and transposed to the lateral hind leg. The nerves were treated with one of three SIS materials, including (i) a nerve cap with spiraling chambering, termed spiral nerve cap (SNC), (ii) a nerve cap with bifurcated chambers termed chambered nerve cap (CNC), or (iii) an open tube. The surgical control consisted of nerve stumps that were not treated. Overall tissue response, axonal swirling, optical density of axons, and behavioral pain response were quantified at 8 and 12 weeks postoperatively. There were no notable differences between the performance of the SNC and CNC groups. The pSIS nerve caps mitigated aberrant axonal regeneration and decreased neuroma formation and associated pain response. These findings suggest that nerve caps with internal chambers for axonal outgrowth may improve axonal alignment, therefore reducing the likelihood of symptomatic neuroma formation. Impact statement This study provides evidence for using nerve caps with internal structure on nerve stumps after amputation surgeries to reduce or prevent symptomatic neuromas. This study showed that porcine small intestine submucosa had a favorable remodeling profile and tissue response, illustrating that this device can be used to (i) minimize soft tissue attachments around the nerves that are capped, (ii) align axonal outgrowth to guide nerve regeneration away from aberrant neuroma formation, and (iii) act as a barrier between the nerve and external stimuli ultimately remodeling into a new soft tissue layer around the nerve stump thus decreasing symptomatic neuroma formation.