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Common peroneal nerve decompression, neurolysis and wrapping with the AxoGen AxoGuard nerve protector

    Overview

    Learn the Common peroneal nerve decompression, neurolysis and wrapping with the AxoGen AxoGuard nerve protector surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Common peroneal nerve decompression, neurolysis and wrapping with the AxoGen AxoGuard nerve protector surgical procedure.
    The common peroneal nerve is vulnerable to injury from direct trauma at the knee or from traction associated with knee dislocation. The presentation is with footdrop due to loss of the function in tibialis anterior and toe extensors supplied through the deep peroneal nerve. In addition there is loss of peroneal tendon function due to loss of the superficial peroneal nerve. There is sensory loss on the dorsum of the foot.
    The decision to operate and decompress the nerve should be made by an experienced nerve surgeon after careful clinical examination, repeated examination if necessary and sometimes supportive imaging and neurophysiological assessments. Typically the decision can be made on the basis of the clinical assessment alone. A dense painful lesion with a positive Tinel’s sign at the peroneal tunnel, a deepening lesion with deterioration under observation, a non-recovering lesion or diagnostic uncertainty are all indications for exploration.
    The surgeon should be prepared for the need for reconstruction in a complete lesion should a rupture or a severe attenuation lesion be identified at surgery. Additional procedures including allograft, autograft and distal motor nerve transfers are covered elsewhere. The AxoGuard nerve protector (AxoGen) is a layered porcine collagen extracellular matrix that can be used to wrap scarred nerves where there is epineurial damage and it rapidly revascularises and restores gliding around injured nerves and acts as a barrier to further scar formation that could impair neural regeneration or cause further deterioration due to nerve tether.
    The case presented demonstrates the decision making in complex nerve trauma and describes the use of an AxGuard to protect a nerve following decompression at the site of injury.

    Indications

    INDICATIONS
    The indications for exploration are a high energy injury with no recovery, neuropathic pain and a positive proximal Tinel’s sign. These factors make a rupture more likely and the surgeon should discuss reconstructive options with the patient including autologous nerve grafting, AVANCE processed nerve allograft and distal augmentation nerve transfers using FDL fascicle to tibialis anterior (tibial nerve to the deep peroneal nerve) and soleus fascicle to peroneus longus (tibial nerve to superficial peroneal nerve). If the nerve is in continuity in a scarred bed then a barrier to scar formation may provide a useful adjenct to simple decompression. The AxoGuard nerve protector is a porcine collagen membrane that revscularizes and provides a healthy gliding layer around injured nerves.
    SYMPTOMS & EXAMINATION
    The patient sustained a high energy sporting injury to the knee with a ligament injury 8 months previously and the peroneal nerve was non-functioning from the time of the injury. There was no sensory function in the common peroneal nerve and no motor recovery. Neurophysiology studies had demonstrated complete denervation with no reinnervation changes seen in the affected muscles. Clinical examination demonstrated a positive Tinel’s sign at the proximal peroneal tunnel. There was some neuropathic pain in the superficial peroneal territory.
    IMAGING
    Imaging of the nerve was not planned as it was decided that the nerve should be explored. Ultrasound can demonstrate a physical continuity of the nerve sheath but cannot predict axonal regeneration.
    ALTERNATIVE OPERATIVE TREATMENT
    The options are to explore the nerve and excise and graft using autologous graft or AVANCE processed nerve allograft. A distal nerve transfer may be performed in late presenting high grade lesions with long nerve gaps where the functional outcome from the nerve graft is usually poor. An alternative strategy is to delay surgery until it is clear that there has been no spontaneous recovery and undertake tendon transfers using tibialis posterior to anterior and FDL to EDL transfers at 12-18 months post injury.
    NON-OPERATIVE MANAGEMENT
    Non-operative management is expectant awaiting some spontaneous recovery. Trophic muscle stimulation may be employed to try and extend the potential window for successful innervation, however there is no strong evidence for this technique. The functional deficit from the foot drop may be treated using an ankle foot orthotic splint.
    CONTRAINDICATIONS
    The contra-indications to surgery at the knee include active infection and a poor soft tissue envelope. A relative contra-indication to use of a porcine collagen wrap may be islamic faith and the options should be discussed is detail with each patient.

    Setup

    Consent should include the option of nerve decompression, stimulation and reconstruction, nerve wrapping or distal transfer or combinations thereof depending on the findings.
    Surgery is typically performed under general anaesthesia with no long acting neuromuscular paralysis to allow intra-operative nerve stimulation to be used to assess for continuity and recovery potential of the common peroneal nerve.
    The patient is positioned in the lateral position with the operated side uppermost. This allows access to the peroneal tunnel and to the ipisilateral sural nerve, if harvest is needed for reversed sensory autograft reconstruction for a rupture or to reconstruct a gap following resection of a neuroma in continuity.
    Basic instruments, a Mixter, sloops, a nerve stimulator, microinstruments, operating microscope, Tisseel fibrin glue +/- AVANCE processed nerve allograft should be available.
    A thigh tourniquet is applied with padding.
    The dependent leg should have a TED stocking and a pneumatic thromboembolic prevention device (Flotron).
    Antibiotics are administered prior to tourniquet inflation in case a wrap or allograft is used.
    A WHO checklist is completed prior to commencement of surgery.



    Operation – 1

    The leg is elevated, the tourniquet inflated and the skin prepped and draped from above the knee leaving th efoot and ankle exposed so that the effects of nerve stimulation may be assessed fully.

    The operating surgeon stands on the posterior aspect of the knee.

    The fibula head if marked and the incision for exposure of the peroneal tunnel. In this case an additional proximal and medial potential extension to the flexor crease of the knee is marked in case a nerve transfer from the soleus branch of the tibial nerve is indicated to the superficial peroneal nerve.

    The skin is incised from the fibula head distally along the roof of the peroneal tunnel.

    Diathermy with an epitome blade may be used for the superficial exposure. It is important to note that the peroneal nerve is close to the skin at this point and monopolar diathermy should only be used as far as the deep fascia.

    The dissection continues along the full length of the peroneal tunnel incision to the deep fascia.

    The course of the nerve along the fibula neck can usually be palpated unless there is a nerve rupture. If not palpable I advise a more proximal exposure posterior to the biceps femoris sheath insertion to the fibula head.

    The fascia overlying the peroneal tunnel is incised and then this plane is developed dissecting with Jamieson scissors.

    The roof of the peroneal tunnel is being opened. Care should be taken when exposing the nerve and particularly when dissecting in a distal to proximal direction due to the risk of damage to nerve branches by dissecting into the “axilla” of the nerve branch.
    The articular branch to the proximal tibio-fibula joint arises from the medial side of the common peroneal and runs in close proximity to the deep peroneal nerve in the second and third parts of the peroneal tunnel.

    A thickened and scarred nerve is identified and a fine tipped 90 degree Mixter forceps is passed deep to the nerve so that a sloop may be placed around the nerve to facilitate neurolysis in the scarred bed.

    A yellow sloop is passed around the common peroneal nerve in the proximal part of the peroneal tunnel.

    In the distal part of the peroneal tunnel there is dense scar adherent to the epineurium.

    Dissection in this area should proceed with great care because intraneural dissection may inadvertently occur due to indistinct tissue planes and uncertainty around continuity of the peroneal nerve.

    As the dissection progresses distally a circumferential neurolysis is achieved using the sloop to maintain tension in the nerve and to gently retract and position it as needed to perform the scar release. The nerve appears mildly attenuated with redundancy. This is sometimes seen in attenuated continuity lesions of in the proximal part of a nerve above a complete rupture.

    Nerve stimulation is performed to assess whether there is any functional continuity of the distal peroneal nerve. In this case there were no contractions in superficial or deep peroneal nerve innervated muscles even with a stimulation of 5mA. A normal intra-operative stimulation would be in the range 0.05-0.2mA.
    The deep peroneal component has been identified distally and tagged with a second yellow sloop. The superficial peroneal nerve component has been tagged with a blue sloop.

    It is imperative that all fascicle groups are stimulated in turn in case there is a partial functional continuity in the nerve. Here the superficial component is being stimulated.

    The stimulation needle should be positioned at multiple points both circumferentially around the nerve and longitudinally along each fascicle group in case there is a localised conduction block from handling and retraction. In focal nerve injuries there may be an area of demyelination resulting in a conduction block but the nerve may have a normal stimulation threshold distal to the zone of demyelination.

    The distal part o f the peroneal tunnel has a thick septum between the peroneal and anterior compartments that must be fully released. Excision of a piece of the septum reduces the risk of scar causing recurrent compression.

    Here the deepest component of the septum is being released from the deep peroneal branch to the tibialis anterior.

    The nerve is decompressed proximally around the fibula neck and traced posterior to the biceps femoris insertion to the popliteal fossa.

    There is circumferential scarring around the nerve still at this level. The scar involves the epineurium.

    Care should be taken during the neurolysis to prevent inadvertent opening of the nerve sheath and intraneural dissection.

    The proximal neurolysis has been completed and the nerve is ready for repeat electrical stimulation to assess for preserved function.

    There is preserved fascicle structure palpable within the nerve and the epineurium is deficient in places exposing fascicles. The nerve is attenuated suggestive of a significant traction injury with plastic deformation.

    In this first part of the peroneal tunnel the fascicle structure is obvious.

    Operation – 2

    In the second and third parts of the peroneal tunnel at the fibula neck and at the lateral-anterior septum there is more attenuation and thinning of the nerve. A fascicle structure is still seen, however the condition of the nerve is concerning. The presence of a fascicle structure implies that there may be some component of the nerve at a Sunderland grade 3. If there is disruption of the perineurium then the grade is automatically a Sunderland 4 and a neuroma in continuity will result.

    The nerve is thicker proximally and there is some scar of the interfascicular epineurium palpable. Deciding what to do next is probably the most challenging decision in nerve surgery. A rupture can be grafted using autologous sensory nerve or processed nerve allograft. An adjunctive distal nerve transfer an be added in such cases if the graft is long, the patient presents late of the proximal nerve quality is uncertain due to extensive longitudinal scar.
    An intact nerve may develop a neuroma in continuity and the surgeon must decide whether to excise nerve tissue prior to reconstruction

    A number of factors are used in determining whether to excise a segment of damaged nerve and to attempt graft reconstruction:
    Associated injuries
    The time from injury
    Recovery to date
    Fascicular structure present
    Intra-operative stimulation findings
    Distance from graft to muscle
    Importance of the nerve
    Other reconstructive options available
    Intraneural neurolysis may be performed to assess for fascicle continuity through the zone of injury. The scarred epineurium is excised and individual fascicles identified and decompressed from within the intraneural scar.

    The plane between the epineurium and the fascicles is being dissected with curved microneural serrated scissors.

    Scarred epineurium is debrided away from the fascicles. This would normally result in damage to the epineurial blood supply, however this tissue is scarred and is causing compression of the fascicles.
    Following the decompression and internal neurolysis there is still no electrical stimulation detectable to the distal muscles.
    At this point the decision on reconstruction must be taken.
    The delay from injury to presentation and the long zone of injury measured at least 8cm means that graft reconstruction in unlikely to restore motor function in the time available for reinnervation (4 months)
    The distal zone of injury is uncertain as the nerve is thinner and grafts would need to be placed directly on to the motor points of the muscles
    The option of a graft and a distal adjunctive nerve transfer (FDL to Tibialis Anterior; Soleus to Peroneus Longus) whilst on the face of it is an attractive option, requires at least 3-4cm of distal nerve motor branch to be undamaged to allow nerve transfer without and interpoistioned graft. This will not be possible as the motor branches are still within the zone of injury. This makes the nerve transfer option unappealing.
    The intact FDL can be used as a tendon transfer to EDL with a standard tibialis posterior to anterior tendon transfer for useful function without need for an ankle foot orthosis.
    The tendon transfer option can be delayed to establish whether the neurolysis have been effective
    The absence of conduction doesn’t mean that there won’t potentially be some recovery through the damaged segment where the fascicles can be traced distally through the injury zone. Absent MUPs imply that there is axonopathy rather than a persistent conduction block
    A nerve wrap may replace the damaged epineurium, encourage vascularised gliding of the extra-epineurial tissues / meoneurium and prevet further scar tether and neurostenalgia
    If the case had been explored at the time of injury, an expectant policy could have been employed for 3 months prior to a decision to excise and graft.
    If a rupture was found it would have been acutely grafted.
    Exploration at 3 months with no recovery may persuade the surgeon to excise and reconstruct in the hope of some recovery over 9 months (12 month reinnervation window closes).
    Early exposure of a high energy injury is always helpful to provide a prognosis and an baseline assessment for subsequent follow up. Failure to progress in line with expectation os then an indiction for further exploration and reconstruction.

    An AxoGuard nerve protector is chosed to wrap the damaged area.
    Two 10 x 40mm wraps are selected and soaked in saline for a few minutes to soften them for ease of handling.

    The AxoGuard protectors have a memory and will readily coil around a nerve.

    Two wraps in position covering the full length of the damaged nerve.

    They should be loosely sutured to themselves with a monofilament 8’0 nylon suture to maintain their position. In an areas where a nerve has significant glide / mobility, I would recommend a single suture at each end between the protector and the epineurium.

    The wraps have been sutured in place around the damaged nerve and the wound is ready for closure after local anaesthetic block of the surgical field.

    Long acting local anaesthetic is delivered around the nerve and as a field block to the wound edges.

    Topical local anaesthetic is delivered to the nerve.

    The wound is closed in layers with absorbable sutures.

    The wound ready for dressings.

    Steristrips are applied to the wound edges.

    An occlusive dressing is applied. This should remain in place for 5-7 days unless the patient develops a possible wound complication requiring a wound assessment.

    A bulky wool and crepe support dressing is applied across the knee. This can be reduced at 48 hours post-operatively.

    The completed dressing.

    Post Operative

    The patient can fully weight bear but is advised to elevate the limb when at rest for 48 hours.
    The dressing can be reduced at that stage and the occlusive wound dressing should be kept in place for 5-7 days.
    The wound can be left open from 12 days and scar massage commenced with moisturiser from 3 weeks.
    Functional assessment and propagation of a Tinel should be assessed at 6 weeks and 3 months.
    EMG at 3 months can indicate whether there is any reinnervation following the neurolysis.
    No recovery by 10 months from surgery should warrant consideration of tendon transfers at the 18 months post injury point.

    Recommended Reading

    Animal studies ave demonstrated excellent revascularisation after implantation with histology studies showing full incorporation and development of an epineural covering to damaged nerves and restoration of extra-epineural gliding surfaces.
    Clinical case series in nerve injury are limited and it is difficult to standardise the extent of trauma. In revision surgery for nerve compression there are papers reporting favourable outcomes when using the protector as an adjunct to neurolysis.
    I use an AxoGuard nerve protector when there is epineural loss, extensive scar and trauma to a nerve that may otherwise tether and cause neurostenalgia. I have re-explored one at a carpal tunnel in a revision surgery that required further exposure for a tenolysis and the AxoGuard had full revascularised with excelent nerve glide. There was less glide at the proximal and distal limits of the original AxoGuard where scar had resulted in localised tether points to the native epineurium.
    Publications:
    Papatheodorou LK, Williams BG, Sotereanos DG. Preliminary results of recurrent cubital tunnel syndrome treated with neurolysis and porcine extracellular matrix nerve wrap. J Hand Surg Am. 2015 May;40(5):987-92
    12 patients were followed for a mean 41 months following revision cubital tunnel surgery. there were improvements in grip, sensation and pain following implantation if the AxoGuard protector. There were no complications.
    George SC, Boyce DE. An evidence-based structured review to assess the results of common peroneal nerve repair. Plast Reconstr Surg. 2014 Aug;134(2):302-311
    The results of this non-systematic review suggest that the outcome for a graft of greater than 12cm is extremely poor and that for those of less than 6cm 64% have a useful functional recovery. Late reconstruction after 12 months results in poor outcome.

    Reference

    • orthoracle.com

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