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Dorsal cutaneous ulnar nerve reconstruction using Axogen Avance nerve allograft

    Overview

    Learn the Dorsal cutaneous ulnar nerve reconstruction using Axogen Avance nerve allograft surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Dorsal cutaneous ulnar nerve reconstruction using Axogen Avance nerve allograft surgical procedure.
    This 35 year old woman developed severe pain in the distribution of the dorsal cutaneous branch of the ulnar nerve following percutaneous K-wire placement for fixation of a 5th metacarpal fracture.
    By the time she presented to a peripheral nerve clinic some months later, she had non-resolving pain and diminished sensation, both confined to the same cutaneous branch territory. This was suggestive of a neuroma in continuity. Sensation on a visual analogue scale was graded at 2/10. However, she had additional features of central sensitisation including spontaneous pain, allodynia and hyperalgesia.
    This section will cover some of the pre-operative and intra-operative decision making in treating such nerve injuries, and will detail a technique using an Axogen Avance nerve allograft to reconstruct the nerve.
    Nerve pain in this scenario resulted from direct injury to the nerve at the time of the index procedure. From a surgical perspective therefore, the pain may be due to:
    Scar tether around the nerve without significant injury to the intrinsic structure of the nerve.
    A neuroma in continuity
    An end neuroma
    In theory, reestablishing continuity across the damaged nerve segment should restore function and minimise and contain axon sprouting whilst re-establishing normal conduction pathways, thus bringing about a successful resolution of symptoms. In practice this is not always effective or even feasible.
    Whether or not to reconnect a nerve is a decision that will depend on a number of factors. For example, a densely scarred bed risks non-resolution or recurrent scar tether and pain. In such scenarios, relocation of the proximal nerve stump into muscle or bone, and the use of a nerve capping devices have been advocated with varying degrees of success.
    However, in areas of critical sensation where the bed is suitable and the distal stump is available, nerve autograft or processed nerve allograft may be used to re-establish continuity after excision of the damaged segment. Here, allograft carries the advantage of avoiding a potential secondary site of nerve pain at the donor site in a patient with established central sensitisation.
    This case illustrates use of a human Avance nerve allograft developed by Axogen inc. which is processed to degrade cellular and non-cellular debris leaving behind an extracellular matrix scaffold. In the UK its use is currently monitored by the National Institute for Health and Care Excellence (NICE) and may be used with special arrangements for clinical governance, consent and audit or research.

    Indications

    INDICATIONS:
    Nerve pain resulting from a neuroma in continuity, an end neuroma, or scar tether should be considered for exploration, if symptoms fail to respond to appropriate non-operative strategies. Some of these are listed below.
    Surgical intervention is more likely to be successful if targeted at the correct nerve trunk. In many instances this can be difficult to determine without the aid of a series of diagnostic nerve blocks using local anaesthetic. Abolition of painful responses following single nerve trunk blockade provides a clear target for surgery. However, it is well recognised that abnormal pain signals may also arise from intact nociceptors supplied by adjacent nerves that share some innervation territory with the injured nerve. Furthermore the exact anatomical location of nerve injury is sometimes not clear at the outset and of course, there may be more than one nerve branch injured. At least a 50% reduction in pain score following targeted anaesthetic blockade is required before surgery is contemplated.
    In this case a neuroma in continuity was treated with excision and grafting using processed nerve allograft. In the UK NICE specifies the requirements for use of allograft which include a clear pathway of governance, consent and audit.
    This patient had significant preservation of sensation within an important cutaneous territory, a well demarcated injured segment of nerve and an excellent response to local anaesthetic blockade of the dorsal cutaneous branch of the ulnar nerve alone. These factors suggested that surgical treatment to re-establish continuity would offer a good chance of restored sensation and reduction in pain by removing the damaged nerve segment, containing axon sprouting and re-establishing normal conduction pathways.
    SYMPTOMS & ASSESSMENT:
    The patient presented with diminished sensation on visual analogue and Semmes-Weinstein monofilament testing. She complained of rest pain that came on intermittently and spontaneously. She described allodynia and hyperalgesia. Although this was most markedly present within the dorsal cutaneous territory it extended to the volar aspect of the ring and little finger.
    There was dry skin and absent sweating due to sudomotor denervation. There was a scar overlying the site of previous wire placement with a Tinel-Hoffman’s sign present here.
    The wrist and digits had a full range of active and passive motion but passive flexion of the wrist reproduced pain, possibly evidence of neurostenalgia, (caused by a increased tension across a tether point where the nerve was adherent to extrinsic scar), However it is important to recognise that axon sprouts within a neuroma have an increased mechano-sensitivity in any case.
    INVESTIGATION:
    Nerve conduction studies showed minimal conduction in the dorsal cutaneous branch territory. A targeted nerve blockade with injection of 0.5mls of 2% lignocaine around the dorsal cutaneous branch of ulnar nerve, proximal to the site of injury successfully abolished pain for a few hours.
    A plain X-ray demonstrated satisfactory union of the original fracture.
    An ultrasound scan was not performed in this case but may be useful in select cases to demonstrate a neuroma or a lack of continuity in the nerve. As a dynamic imaging modality it may be used to demonstrate lack of normal nerve gliding within a scarred bed.
    OPERATIVE ALTERNATIVES:
    Alternative surgical treatments include:
    Simple neurolysis with or without wrapping the nerve with a barrier device
    Excision of the neuroma and reconstruction with autograft
    Excision of the neuroma and relocation of the proximal stump – a variety of methods have been described
    The method selected should take into account the nature of the original injury, duration of symptoms and previous management as well as severity of current symptoms. As stated above, factors that provoke pain as well as response to diagnostic blocks is also important. Often the final decision is made intra-operatively once the neuroma has been visualised.
    Where there is doubt about the degree of continuity through a neuroma in continuity, intra-operative nerve conduction testing may prove a useful adjunct. This is also useful in cases where part of a nerve trunk has regenerated leaving specific neuroma fascicles that require excision and grafting.
    Some surgeons argue for crushing the nerve stump proximal to the site of neuroma excision to initiate a new axonotmetic injury as an essential step for a successful outcome.
    NON-OPERATIVE ALTERNATIVES:
    In neuroma pain, non-operative modalities of treatment should be commenced early whether or not surgery is contemplated. Therapy should continue in the post operative period. Neuropathic pain agents such as gabapentin and pregabalin are widely used in conjunction with opioids and other simple analgesics. Topical anaesthetic agents or capsaicin may be tried although effectiveness varies widely between patients.
    A hand therapist trained in the treatment of neuropathic pain is essential. Treatment should be tailored to individual patients. This may include neural glide and muscle strengthening exercises. Techniques also include desensitisation for hyperalgesia including different types of sensory stimulation, including vibration and texture to re-educate and desensitise. Centrally targeted therapies such as mirror therapy can aid cortical remapping. Further elaboration about therapy in this area is perhaps beyond the scope of this surgical guide but references at the end of the section are included for further reading.
    CONTRAINDICATIONS:
    Careful pre-operative counselling is important and surgery may not be appropriate if there are signs of ongoing nerve recovery and/or ongoing improvement in symptoms following a course of hand therapy.
    Active infection is a contraindication.
    A poor response to diagnostic local anaesthetic blockade may herald a poor outcome to surgery.
    In a severely scarred surgical bed the nerve may simply re-tether to extrinsic scar and therefore a relocation type procedure may be more appropriate. Equally an area of poor soft tissue cover or one exposed to repeated trauma may remain sensitive despite improved conduction into the distal nerve territory.

    Setup

    The patient underwent regional anaesthesia by means of an axillary nerve block.
    A standard operating arm table and upper arm tourniquet were used.
    Bipolar diathermy, good lighting, micro-instruments, loupe magnification and an operating microscope are all essential tools.

    Operation

    Pre-operative markings are made.
    It is useful to mark out the point where the Tinel-Hoffman sign is elicited and of course there may be more than one over the course of the nerve. An experienced examiner can differentiate a true Tinel-Hoffman sign from background allodynia.
    In this case the nerve injury was potentially caused by a percutaneous wire. Therefore the original entry point of the wire is also marked out as one may expect dense scar or even a neuroma at this level.

    Careful dissection through the skin and superficial fascia is important. Here the original scar made by the percutaneous wire could be traced through the superficial layers and lay directly over the nerve.
    Superficial veins require retraction or coagulation with bipolar diathermy.

    Exposing the nerve was straightforward but can be made difficult by dense scar orwhere there is doubt about nerve continuity. The principle in these situations is to widen the exposure and find the nerve in uninjured tissue, and work back to the injured segment.
    Once the nerve is identified, a useful technique is to continue further dissection over the nerve in line with its course and any branches.
    The nerve is identified with a short segment enveloped in scar tissue.

    It is important to expose the proximal and distal nerve outside of the area of injury

    After this is done the nerve is gently freed from the scar with blunt dissection.
    One can see the distal branches clearly here but the central portion overlying the extensor tendon is thickened and less easily defined.

    Micro-instruments will be more useful after the nerve anatomy has been clearly delineated and much of the scar dissected away.

    Now, micro-instruments are used to dissect away some of the adhesions and a neurolysis is performed.

    This is the proximal nerve trunk and appears normal in diameter, consistency and mobility and is therefore beyond the injured segment.

    The microscope can now be brought into the operating field. As with all equipment, it is important to set this up prior to starting the procedure.
    This will allow further delineation of nerve anatomy and inform decision making about how to treat the injured nerve segment.

    Under increased magnification, it is clear that there is a neuroma in continuity present.
    Some further neurolysis may help here.
    In the case of a cutaneous nerve with a patient under a regional block anaesthetic, it is difficult to ascertain the degree of continuity through the neuroma. Microscopic appearances must be interpreted in light of the pre-operative investigation results and clinical findings to arrive at a suitable course of action.
    In this case there is very little continuity clinically with a great deal of neuropathic pain. Clinically the central portion of the neuroma segment is hard and woody and the distal nerve branches feel less well defined than the proximal segment which feels more ‘full’.
    Overall appearances suggest that reconstruction with nerve graft is likely to provide the best chance of restoring a degree of continuity to the nerve. Although the use of nerve autograft is an established technique and would be a reasonable option here, the severe neuropathic pain and the evidence of central sensitisation suffered by this patient may be exacerbated by a second site of surgery and sacrifice of a different, normal nerve.
    In this scenario, it was felt that processed nerve allograft would restore continuity over this short segmental defect whilst avoiding a second site of sensitisation. Some protective sensation would be the minimum expected functional recovery.

    The neuroma is first excised.
    Both proximal and distal nerve ends are then sliced sequentially until healthy, non-scared nerve tissue is visualised. Proximally one should look for normal fascicle architecture and endoneurial bleeding. The tourniquet may be released to confirm this.
    Inadequate excision in order to minimise the final gap may compromise the eventual outcome.
    A fine blade or a neurotome may be used to ensure thin sections can be made with minimal handling of normal nerve tissue.

    The processed nerve allograft (Axogen inc.) is thawed and soaked in normal saline. It is then sutured into place using 3-4 epineurial sutures. 9/0 ethilon sutres are suitable for this 2-3mm x 20mm allograft.
    Handling of the allograft is minimised as success of this technique is highly dependent upon the integrity of its endoneurial tubular microstructure.

    After distal suture placement the proximal end of the allograft is trimmed to an appropriate length and sutured into place. Tension across the construct must be minimised.

    The final length of the gap is measured and the location of the proximal and distal neurorrhaphy sites in relation to superficial skin markings is recorded.
    This will allow accurate monitoring of progress by following the Tinel-Hoffman sign as it progresses through the allograft and into the distal network of nerve branches.

    The wound is irrigated. Any ongoing bleeding is dealt with prior to closure.

    A few deep dermal sutures are followed by a continuous subcuticular closure with an absorbable monofilament suture.
    Steristrips and a non-adherent dressing are applied.

    A bulky soft dressing is applied.
    The arm is elevated and protected in a Bradford sling.
    The patient may be discharged home the same day if pain control is adequate.

    Post Operative

    Dressings are removed after 7 days in a dressing clinic to allow a wound inspection, followed by early initiation of nerve gliding exercises and supervision of a hand therapist. Analgesia, particularly neuropathic agents should be continued in this early period. A simple dressing should remain covering the surgical wound until 2 weeks when any suture trimming takes place.
    The patient will require regular hand therapy over the first 12 week post operative period. Analgesia may be slowly reduced during this period as pain levels improve.
    Progress of neural regeneration is examined for in clinic. A progressing Tinel’s sign is a reliable sign of progress. Repeated Semmes-Weinstein monofilament examination, pain scores and a PROM score of the surgeons choosing should be repeated at 3-6 monthly intervals to quantify recovery and guide further decision making.

    Recommended Reading

    The results of non-operative management of neuroma pain remains poor with only 30% of patients obtaining satisfactory pain relief. Surgery can offer an effective alternative but reported results are variable and treatment protocols differ widely. The use of pre-operative sensory mapping and diagnostic blocks to guide surgical management is increasingly being used and may increase the effectiveness of surgery.
    The use of processed nerve allograft to reconstruct nerves after neuroma excision is gaining interest although few published results are available. One recent study found significant improvements in pain after reconstruction with allograft.
    Chen Y, Devor M. Ectopic mechanosensitivity in injured sensory axons arises from the site of spontaneous electrogenesis. Eur J Pain 1998;2:165–78
    Impaulse pattern analysis in a rat model was used to show that increased mechanosensitivity and spontaneous activity are features of the same underling neurological injury
    Tal M, Bennett GJ. Extra-territorial pain in rats with a peripheral mononeuropathy: mechano-hyperalgesia and mechano-allodynia in the territory of an uninjured nerve. PAIN 1994;57:375–82
    This rat based study examines the central pathways for pain that occurs outside the territory of an injured nerve. Extra-territorial pain is a normal part of nerve injury, seen in both animals and human subjects.
    Von Hehn CA, Baron R, Woolf CJ. Deconstructing the neuropathic pain phenotype to reveal neural mechanisms. Neuron 2012;73:638–52.
    This study argues for an individualised treatment of neuropathic pain since pain responses differ so widely between subjects. Putative mechanisms for central sensitisation are also examined.

    Valérie Decrouy-Duruz et al Evaluation of surgical treatment for neuropathic pain from neuroma in patients with injured peripheral nerves. J Neurosurg. 2017 Jun 16:1-6
    335 nerve injuries in 231 patients were evaluated for factors associated with relief of neuropathic pain. surgery was shown to be an effective treatment modality and patients underwent a variety of procedures. The authors advocate pre-operative diagnostic nerve blockade to map out the injured nerves to increase the success rate of surgery.
    Souza JM et al. Treatment of Foot and Ankle Neuroma Pain With Processed Nerve Allografts. Foot Ankle Int. 2016 Oct;37(10):1098-1105
    This study reports the results of treatment of cutaneous neuromata in the foot and ankle using a processed nerve allograft. 22 patients were treated and a significant reduction in pain scores was reported although sensory outcomes were not recorded. The authors state that the cost of the allograft was offset by the reduced theatre time and elimination of donor site complications.

    Reference

    • orthoracle.com

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