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Median nerve neurolysis, resection and reconstruction using Axogen AVANCE processed nerve allograft

    Overview

    Learn the Median nerve neurolysis, resection and reconstruction using Axogen AVANCE processed 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 Median nerve neurolysis, resection and reconstruction using Axogen AVANCE processed nerve allograft surgical procedure.
    The median nerve is superficially placed at the wrist crease and is vunerable to injury. In this case there was a laceration to the median nerve that had occurred some 24 months previously. There was a delayed presentation and no surgical exposure was undertaken to explore the nerve at the time. The patient reported poor sensory recovery in the hand and constant neuropathic pain in the median nerve territory. There was a swelling within the nerve at the site of previous injury which was sensitive to local touch, eliciting severe neuropathic pain exacerbations with wrist extension and finger flexion. There was intact innervation to the thumb pulp and to the thenar muscles. A diagnosis of partial neuroma in continuity was made and the patient was considered for exploration, resection of the neuroma and reconstruction.
    AVANCE (AxoGen Inc. Alachua, Florida, USA) processed nerve allograft was discussed as the patient was not willing to consider use of autologous graft with risk of further neuropathic pain at the donor site. The nerve was therefore reconstructed using an AVANCE allograft after meticulous intraneural dissection allowed preservation of the intact fascicles to the thumb.
    In cases where there is some sensory preservation, consideration may be given to neurolysis and wrapping of a neuroma in continuity to diminish local mechanical irritation or nerve tether pain (neurostenalgia). Collagen nerve wraps and bio-resorbable polymer membranes can be used to diminish further post-operative scar tether at the level of the painful neuroma.
    Autologous flaps, including the Becker adipo-fascial flap and the radial forearm perforator flap, can be used to provide additional cushioning of the sensitive area in such cases. This case demonstrated complete loss of function in the index and middle fingers and so the option of neurolysis was not considered.
    The gold standard nerve graft option is a reversed sensory autologous nerve with the donor nerve selected based on the length of the defect, the number of cables required, the site of surgery and the type of anaesthesia. Autologous nerve graft harvest leaves a numb area of skin at another site and there can be donor proximal nerve stump neuroma formation. The option of autologous nerve graft may be unacceptable to some patients, particularly when they are presenting with significant neuropathic pain and the concern is that the donor nerve site could become another pain driver.
    An alternative option is to use AVANCE processed nerve allograft. This is human nerve that is acellular having undergone detergent and enzyme washes. It is screened to avoid infection transmission and then provided sterile and frozen in a number of sizes. The graft is provided by AxoGen Inc Alacachua, Fl, USA.

    Readers will also find the following associated techniques of interest:
    Extended approach Carpal Tunnel decompression
    Revision carpal tunnel decompression and application of Polyganics Vivosorb membrane
    Combined median and ulnar nerve decompressions
    Carpal tunnel decompression

    Indications

    INDICATIONS
    The indications for nerve graft reconstruction are:
    A primary nerve injury with traumatic nerve tissue loss
    Delayed presentation with a gap after debridement of non-viable nerve tissue
    A gap resulting from resection of a neuroma in continuity or after resection of a tumour.
    In this case the decision to operate was based on the absence of sensation on some of the median nerve innervated digits. The presence of function within the motor fascicles of the median nerve and the thumb sensation were suggestive of injury to the superficial and ulnar fascicles of the median nerve.
    SYMPTOMS & EXAMINATION
    This patient had local swelling within the nerve with sensitivity to touch and an underlying intrusive neuropathic pain. There was absence of sensation in the index, middle and partial ring finger. The lack of sensation renders these digits prone to injury due to loss of protective sensation. There was a strong Tinel’s sign elicited on tapping at the site of injury and no distal Tinel’s sign. The combination of the proximal Tinel and an absent distal one are suggestive of a neuroma in continuity within the median nerve with effectively no sensory preservation too the effected digits. The presence of motor function in the thenar eminence and the preservation of thumb pulp sensation suggests that the fascicles to the thumb are not involved in the original injury. The original injury would have been a partial transection of the nerve. The dry skin in the digits is a feature of loss of small unmyelinated autonomic sudomotor function in the nerve. This is a feature of axonotmesis or neurotmesis injury.
    IMAGING AND NEUROPHYSIOLOGY
    Ultrasound (US) can confirm the swelling within the median nerve, suggestive of a partial neuroma in continuity. High resolution US could demonstrate some fascicle continuity. US may be too painful to perform due to the contact sensitivity over the neuroma.
    Magnetic resonance imaging (MRI) is an alternative imaging modality that requires no probe contact on the sensitive area. I did not request imaging because the diagnosis is a clinical one that can be elicited with careful systematic clinical examination.
    Neurophysiology studies may demonstrate the absence of sensory conduction to the index and middle fingers with decreased amplitude and slowing of conduction through the injured segment. Electromyography can be used to decide whether there has been any involvement of the motor innervation with reduced amplitude and polyphasic in cases where there has been some reinnervation.
    Neurophysiology studies were not requested in this case because there was a clear clinical diagnosis and no sensory recovery or residual function in the index and middle fingers. Surgery was offered to try and resolve this situation and the patient accepted.
    ALTERNATIVE OPERATIVE TREATMENT
    In cases where there is some sensory preservation, consideration may be given to neurolysis and wrapping of a neuroma in continuity to diminish local mechanical irritation or nerve tether pain (neurostenalgia). Collagen nerve wraps and bio-resorbable polymer membranes can be used to diminish further post-operative scar tether at the level of the painful neuroma.
    Autologous flaps, including the Becker adipo-fascial flap and the radial forearm perforator flap, can be used to provide additional cushioning of the sensitive area in such cases. This case demonstrated complete loss of function in the index and middle fingers and so the option of neurolysis was not considered.
    The gold standard nerve graft option is a reversed sensory autologous nerve with the donor nerve selected based on the length of the defect, the number of cables required, the site of surgery and the type of anaesthesia. Autologous nerve graft harvest leaves a numb area of skin at another site and there can be donor proximal nerve stump neuroma formation. The option of autologous nerve graft may be unacceptable to some patients, particularly when they are presenting with significant neuropathic pain and the concern is that the donor nerve site could become another pain driver.
    An alternative option is to use AVANCE processed nerve allograft. This is human nerve that is acellular having undergone detergent and enzyme washes. It is screened to avoid infection transmission and then provided sterile and frozen in a number of sizes. The graft is provided by AxoGen Inc Alacachua, Fl, USA.
    AVANCE processed nerve allograft can be used in diameters up to 4-5mm and 70mm in length. There is the option to reconstruct a nerve with cabled allograft using smaller diameter allografts in the sam way that autologous cable nerve grafting is performed. The graft may be sutured in place or secured collagen nerve wraps or nerve connectors plus a fibrin glue (Tisseel).
    When a nerve is deemed non-reconstructable (poor bed for grafting, long defect) a distal sensory nerve transfer can be used to provide some protective sensation to the anaesthetic area. The 4th webspace nerve can be used to transfer to the radial digital nerve (RDN) of the index to allow axons from the ulnar nerve to repopulate the empty endoneural tubes in the index RDN and provide protective sensation. This technique bypasses the area of the original injury.
    In cases where there is a complete loss of median nerve function and the primary nerve defect is deemed non-reconstructable, motor nerve transfer from the abductor digit minim to the motor branch of the median nerve combined with either superficial radial nerve terminal branches to the dorsal of them and index sensory transfer to the ulnar digital nerve (UDN) of the thumb and the RDN index or 4th webspace to first webspace ulnar to median nerve transfer in the palm. The restoration of protective sensation to the key contact zones (UDN thumb and RDN index) is the aim of the sensory transfer in this latter situation, rather than restoration of function to the whole median nerve territory.
    NON-OPERATIVE MANAGEMENT
    The neuroma in continuity can be treated with neuromodulation to try and reduce the severity off symptoms.
    CONTRAINDICATIONS
    Contraindications to graft reconstruction are active infection and poor surgical bed with scar. The AVANCE allograft is a useful alternative to autologous nerve graft when a patient refuses autologous graft harvest. The patient must consent to use of allograft in this situation. AVANCE allograft has excellent safety data and excellent efficacy data in digital nerve reconstruction. Reconstruction of non-digital sensory nerves has reasonable efficacy data. There is no good comparative data for AVANCE allograft versus autologous sensory graft in mixed nerve reconstruction. The patient must be aware of the limited evidence base to date. The limitation is due to the relative numbers of nerve injuries and the comparative trials published only in digital nerve reconstruction at the time of writing in 2019.

    Setup

    For cases of median nerve exploration and AVANCE nerve allograft reconstruction, I use brachial plexus regional block anaesthesia. The surgery is performed on a single limb and there is no requirement for lower limb autologous nerve graft harvest. The block is preformed under ultrasound guidance with a combination of local anaesthetic agents to provide a rapid onset and sustained anaesthesia that provides an extended post-operative block for between 8 and 12 hours. When the block is performed at the level of the upper arm a supplementary subfascial block is required to anaesthetise the skin supplied by the intercostobrachial nerve and the medial cutaneous nerve of the arm. The addition of this block ensures that a pneumatic tourniquet can be placed around the upper arm without discomfort should if be required for up to 120 minutes.
    Antibiotics are administered intravenously to cover common skin commensals in advance of the tourniquet insufflation. The antibiotics are used due to the planned implantation of a nerve allograft which will take a few days to vascularise form the bed and the proximal and distal nerve stumps.
    The regional block allows exploration of the site of the median nerve neuroma with a bloodless field. Additionally, the duration of the block ensures that there is sufficient time for a complete neurolysis of the median nerve, resection of the neuroma and reconstruction. Intra-operative nerve stimulation is still possible due to the segmental nature of the conduction block achieved at the level of the local anaesthetic infiltration at the upper arm. The stimulation can be used to map intact function in the fascicles to the thenar muscles. These are functioning at the start of the procedure and the aim is to preserve them and resect the neuroma in the remaining fascicles to the index, middle and ring fingers.
    The hand is exsanguinated and the tourniquet elevated. The skin is prepared with chlorhexidine.
    The arm is draped and the positioned on a side arm table in a supinated position with the and secured in a ”lead” hand.
    The site of planned skin incision is marked. The exposure for the safe exposure of the nerve through the previous scarred bed requires an extensile incision and full release of the carpal tunnel t identify the motor branch of the median nerve and trace the fascicle group back into the main nerve.
    A “V” extension is made across the volar wrist crease to expose the median nerve deep to the ante brachial fascia in the distal forearm.

    Operation – 1

    The site of the maximum Tinels is marked with a cross pre-operatively.
    There are well-healed old deliberate self harm scars on the volar aspect of the forearm. The cross marks the site of suspected neuroma.
    The surgical side is marked with an arrow. The procedure and site are confirmed as part of the World Health Organisation (WHO) checklist at the start of the procedure.

    The clinical examination demonstrates dry skin in the median nerve territory consistent with loss of small fibre autonomic sudomotor function. No autonomic function is consistent with a complete axonotmesis (Sunderland grade 4) peripheral nerve injury.
    The dry skin is indicative of loss of small unmyelinated autonomic sudomotor function in the median nerve territory.
    Small fibre reinervation usually predates large myelinated recovery and the absence of autonomic function at this stage after the injury implies that there has been no functional axonal regeneration across the injury site.

    The limb is prepped and draped and positioned in a “lead” hand.A “lead” hand is an excellent tool for positioning the hand in supination to allow a stable platform for exploration and microsurgical intramural dissection.

    The skin incision is marked for exposure of the median nerve. The incision has a “V” extension to the ulnar side of the wrist to avoid a longitudinal scar crossing the flexion creaseLongitudinal scars can contract due to the tension forces acting across them. The ulnar sided extension also moves the scar away from the median nerve.
    A “stop moment” is triggered to confirm the site of surgery prior to incising the skin.

    The palmar skin is opened distal to the neuroma.The palm is opened as for a simple carpal tunnel decompression. When exposing a nerve in scar the proximal and distal exposure is essential to then guide exposure in the scarred segment. Otherwise there is a risk that the epineurium may be inadvertently opened whilst dissecting in start resulting in fascicle injury.

    The subcutaneous palmar tissues are carefully dissected overlying the flexor retinaculum using tenotomy scissors.Small cutaneous nerve branches arising in the region of the palmar skin can be identified and protected.

    A small self-retaining retractor is positioned between the skin edges in the palm to assist exposure of the palmar aponeurosis.

    The proximal incision is extended to the forearm and the ante brachial fascia overlying the median nerve is identified.
    The hypothenar fat pad is identified in the ulnar aspect of the wound. The fat pad can be mobilised on a vascular pedicle to cover a scarred nerve in revision carpal tunnel decompression.

    A full release of the carpal tunnel is completed from the distal forearm fascia to the superficial palmar arch.The palmaris brevis is seen overlying the flexor retinaculum and it is incised.
    The flexor retinaculum forms the roof of the carpal tunnel and must be incised throughout its length.

    The flexor retinaculum is incised in its central part in the line of the ring finger and the median nerve is identified under the divided flexor retinaculum.The FR is incised and the distal end is exposed with blunt dissection to identify the superficial palmar arch which is the continuation of the ulnar artery at the distal end of Guyon’s canal.

    The FR is partially opened and the median nerve and flexor tendons can be seen in the deepest part of the wound. The self-retaining retractor is adjusted to maintain tension on the wound edges and the cut edges of the FR which needs further release throughout its length.
    FR: Flexor Retinaculum
    MN: Median Nerve

    The flexor retinaculum has been divided throughout its length in continuity with the ante brachial fascia in the distal forearm.There is dense scar at the level of the distal forearm and care should be taken in dissecting the median nerve and neuroma free from the scar tissue to avoid inadvertent nerve injury.

    Neurolysis requires some counter-traction and the adherence of the nerve to scar on the undersurface of the flexor retinaculum can be used to maintain tension on the scrub-nerve interface by using a skin hook to lift the retinaculum.The surgeon should try and identify the plan between th eepineurium and the scarred paraneurium tissue. Turning the scalpel blade so that the blunt back edge is against the nerve and then using the blade to trace along the nerve while pushing the blade backwards allows atraumatic division of the scar.
    Care should be taken when dissecting distal to proximal in a scarred nerve as it is possible to enter the “axilla” of a branch point and cause an injury. Distally there are the common digital nerves, the nerves to the thumb, the motor branch of the median nerve and then proximal to the wrist crease by 5-7 cm is the palmar branch of the median nerve take-off from the radial side of the median nerve.

    The palmar branch of the median nerve is identified proximal in the interval between the median nerve and the fCR tendon, and tagged.Identifying the palmar branch prior to proximal dissection reduces the chance of injury.

    The palmar branch is tagged using a Mixter passed under the branch and a sloop then introduced under the nerve.
    The sloop will allow gentle retraction of the nerve during the subsequent neurolysis. In addition the coloured sloop maintains some protection of the nerve branch by keeping it visible during the neurolysis which is done with loupe magnification, typically with a small field of view. Otherwise there is a risk of injury to structures at the margins of the visible magnified field.

    As the sloop is drawn under the palmar branch, care should be taken to avoid snagging against the deep surface of the nerve and causing an injury.The sloop is used to maintain traction on the nerve whilst the distal palmar branch is identified and dissected from scar.

    The sloop may be used to retract the palmar branch during the neurolysis.
    The neuroma is apparent in the median nerve. The sutures from the repair are just visible.
    PBrMN – Palmar Branch of Median Nerve
    FR – Flexor Retinaculum
    N – Neuroma

    The neurolysis continues along the radial side of the median nerve towards the carpal tunnel.The neuroma is palpable and becoming visible deep to the scissors.
    There are dense adhesions between the old surgical scar and the median nerve at the level of the neuroma.
    N – Neuroma
    A – Adhesions

    The distal palmar branch is dissected to determine whether it is in continuity.
    There was some sensation preserved in the palmar branch of the median nerve. There was absent sensation on the main median nerve territory. There was reasonable preserved function in the motor branch of the median nerve supplying the thenar muscles.

    The ulnar side of the median nerve is now freed.Neurolysis along the median nerve on th ulnar side is simpler as there are no normal branches. It should be noted that in the distal dissection there may be an anomalous communication between the 3rd common digital nerve (CDN) from the median nerve and the 4th CDN from the ulnar nerve.

    The distal part of the ulnar dissection requires great care because if present, the anomalous communicating branches are usually very small.The branch may supply some ulnar sensory innervation to the area typically supplied by the median nerve or vice versa. If injured, there may be some further sensory loss and the risk of a second neuroma compromising the outcome from this surgery.

    The 3rd CDN from the median nerve is dissected from scar and then is tagged with a blue sloop.The distal sloop can be used to help provide traction own the median nerve to assist with dissection of the other CDNs in the distal part of the surgical exposure.

    The motor branch of the median nerve is now identified and released from scar. A clip passed deep to it facilitates passage of a sloop. A red sloop is placed around the motor branch of the median nerve.

    A red sloop is passed around the motor branch of the median nerve.
    Gentle traction on the red sloop facilitates exposure and dissection of the other nerve branches from the median nerve at the distal end of the carpal tunnel.
    There is fat around the 2nd webspace nerve, suggestive that the previous surgical exposure did not extend this far distally.

    The median nerve is now fully exposed in preparation for the neuroma resection.
    A circumferential neurolysis is performed at the level of the neuroma.

    Operation – 2

    A microsurgery background is placed under the median nerve at the level of the neuroma.The size of the neuroma can be measured and the median nerve can be turned to determine whether there is any sparing of the dorsal fibres from what was previously recorded as a partial median nerve laceration and repair.

    Nerve stimulation is used to determine whether there is any residual function in the motor branch of the median nerve.The nerve may have a conduction block following dissection. In addition the tourniquet can induce an ischaemic conduction block. In this case there was some residual function, albeit poorly stimulating. It was decided to try and trace any intact or functioning fascicle from the median nerve to preserve thenar function.
    The assistant’s index finger is placed over the thenar eminence and is feeling for contraction of the thenar muscles during stimulation.
    Normal stimulation thresholds for motor function are approximately 0.1-0.2mA with this set-up. In this case there was only poor contraction with stimulation to 5mA. This is 50x the normal threshold and stimulation at this level should recruit all residual motor axons in the distal part of the median nerve as it branches to the thenar eminence through the recurrent motor branch.

    The stimulator needle is insulated on the outside.
    The tip of the needle should be placed flat against the nerve under test. The bevel should be placed carefully to avoid direct nerve trauma.

    Next the stimulator is used to try and trace any intact fascicles across the neuroma site.The median nerve can be rotated and the stimulator turned down to 1mA to try and prevent recruitment of motor fascicles through any intact sensory fascicles.

    The neuroma is opened and is splayed to examine the fascicular array and determine whether any fascicles can and should be preserved.This is technically demanding and starts with loupe magnification. Once the nerve is opened, the operating microscope is brought in and the dissection continues with higher magnification.

    Nerve stimulation is again used within the neuroma to trace any predominantly motor fascicles.
    There is dense scar within the neuroma and superficially at lest there is no clear fascicular structure. The stimulator can be turned down to 0.05-0.2mA and retested to trace the main fascicles. Note that the fascicles are often mixed motor and sensory, however as the nerve Strats to branch, the fascicles to the motor branch will become mainly motor afferent and efferent fibres.

    There is no good stimulation at this site and so the needle is placed at different circumferential points on the nerve distal to the neuroma to identify the motor groups.
    Anatomically these motor fascicles should be on the deep and radial aspect of the median nerve.
    Note that prolonged tourniquet time of more than 30 minutes will start to interfere with the stimulation and if there is uncertainty, the tourniquet should be released for 15 minutes and the assessment repeated.
    Releasing the tourniquet will render the subsequent dissection and reconstruction more challenging.
    There is dense scar within the median nerve at the level of the neuroma.

    The operating microscope is used to assist with the dissection within the neuroma.There is a fascicle in continuity crossing the neuroma. This will be dissected from the scar to determine whether it should be preserved.

    A mixter followed by a sloop is used to pass under the fascicle that may be suitable to preserve.This will facilitate the passage of a sloop.

    A sloop is passed around the fascicles to be preserved.
    The fascicle is neurolysed from the scar using a scalpel.

    The scar tissue is dissected off the intact fascicles and is sent for histology.
    The proximal extent of the debridement should be until there is no inter-fascicular scar visible on examination of the cut phase of the nerve under operating microscope magnification.

    There are some fascicles identified, however most of these also have intrafascicular neuromas at the site of injury and repair.

    After removal of the neuroma, there is a single remaining fascicle that on stimulation has some function preserved in the thenar muscles.It is worth noting that there are some swellings in the remaining fascicles, suggesting that these were involved in the original injury and have recovered with a partial functioning neuroma in continuity.

    The nerve gap is measured and then a suitably sized Avance processed nerve allograft can be selected for the enabled allograft reconstruction.The proximal debridement must be adequate or there is a risk of further neuroma formation and poor axonal regeneration.

    The allograft is trimmed to the required lengths for a tension free reconstruction.Leaving some fascicles intact prevents the gapping that normally follows complete transection of a nerve due to the longitudinal strain forces due to biotensegrity.
    Avance does not need to be reversed in the way an autologous sensory nerve would be reversed when cable grafting to prevent axonal escape of regenerating axons along side branches.

    A sequential building up of the nerve gap is performed using cables of the nerve allograft.The fascicle groups in the proximal and distal stumps can be matched, however due to inter-fascicular branching the two cut faces ion the nerve stumps will not have an exact match of fascicle patterns.

    `the cables of nerve allograft are positioned in the gap and then each will be sutured using 9’0 nylon, microsurgical instruments and magnification with the operating microscope.The placement of the grafts should be so that there is no distortion of the nerve ends and good cover of the cut nerve face with apposition of the fascicles in the parent nerve and the fascicle groups seen in the nerve allograft.

    The final reconstruction is ready for suturing and then supporting with a fibrin glue.
    There is good matching of the fascicular content of the nerve.

    2-3 x 9’0 sutures are placed at each end of each cable of nerve allograft.the allograft is sutured to the parent nerve epineurium with each fascicle group covered completely with nerve allograft.

    the distal co-aptation sites are completed.the nerve is well-aligned and the suture neurorraphies can be augmented with Tisseel fibrin glue.

    the nerve allograft reconstruction is supported with fibrin tissue glue prior to closure.Fibrin glue supports the nerve reconstruction and provides a temporary barrier too scar. Fibrin glue confers additional strength for 10-14 days following the repair.
    the microsurgery background material can be used to wrap the fibrin glue coated reconstruction while the fibrin clot forms. This provides a circumferential conforming layer of fibrin around the whole reconstruction.

    The reconstruction is completed and haemostats is performed prior to wound closure.The length of the reconstructed segment should be recorded as well as the location of the proximal and distal co-aptation sites from a fixed boney landmark. This facilitates monitoring on the post-operative period when the rate of the Tinel’s sign progression can be used to assess the progress of the regenerating axons.

    Interrupted sutures are used in case of haematoma in the post-operative period that is a complication of neurolysis. A few sutures can be removed if required to evacuate any haematoma.

    The completed wound closure with a v extension to the ulnar side across the wrist will reduce the tension forces acting along the scar during active wrist extension.

    The completed wound closure with interrupted sutures.
    The wound will be covered with a non-adhesive fenestrated dressing. I prefer `mepitel as this allows blood to pas through but it maintains a non-adherent layer over the sutures.

    Operation – 3

    Dressing gauze is placed over the closed wounds & a cast applied

    Wool wrapping of the dressings should leave the MCPJs free.
    The wool should be loosely wrapped to prevent constriction when the tourniquet is released and the limb swells in the post-operative period.

    Wool bandaging is applied to the limb from the MCPJs to the mid forearm.

    Bandaging is applied and then a volar slab as far as the distal palmar areas.
    The slab portion should support the wrist with 15-30 degrees of extension and allow fiull flexion of the MCPJs.

    A volar slab is applied to the wound dressings.A well-padded dressing is applied including a wool wrap and then a volar Plaster of Paris slab is applied to keep the wrist still, but allowing some digit motion to prevent recurrent adhesions.

    Post Operative

    The operation WHO “sign-out”is completed and the surgical team will complete the operation record, the post-operative prescriptions and the discharge summary. The rehabilitation plan is put in place and the patient is informed about the procedure and the expected recovery going forwards.
    The limb is placed in a Bradford sling for elevation and protection whilst under persisting regional block anaesthesia.
    The patient can be discharge the same day with plans for dressing reduction and wound inspection at 7-10 days post-operatively.
    The wrist can be moved at that stage and the patient is encouraged to mobilise the digits.
    Neuromodulator medications may help in the management of neuropathic pain in the post-operative period.
    During the recovery phase there is no protective sensation in the radial digits and the patient must be taught to keep the skin soft and supple using emollient creams. There is a risk of thermal injury and trophic ulceration.
    The joints in the thumb should be kept mobile and the use of a thermoplastic splint to hold the thumb in a mid-palmer abduction and mid-opposition position may encourage functional use of the hand.
    The Tinel’s sign progression can be used to evaluate axon regeneration rate. A create of 1mm per day is expected after a graft reconstruction with a lag of 2 weeks. In nerve allograft it is my experience that the lag is longer at perhaps 4 weeks and the rate of regeneration is slower than for autograft, perhaps because of the need for more cellular migration to the allograft than for autologous graft.
    The quality of the regeneration can be assessed with the differential Tinel’s sign. Stronger tingling at the distal regenerating nerve front than at the proximal reconstruction site implies a good quality repair whilst inverse with stronger proximally may imply axon hold-up at the co-aptation site and could represent a poorer quality repair with scar formation.
    Early signs of nerve recovery are the restoration of autonomic vasomotor and sudomotor function in the hand in the territory of the median nerve. thee fibres are small and unmyelinated. They grow more rapidly than the larger sensory fibres that require mature myelin sheaths for normal function. as such the restoration of the autonomic fibres is a precursor of sensory recovery. Sensory recovery can be evaluated with the Semmes-Weinstein monofilament p[ressure threshld testing and the static and moving 2-point discrimination tests.
    Normal monofilament thresholds are 0.04 – 0.2g. Normal S2PD is 5mm and M2PD 3mm in a young adult.
    Motor functional recovery is usually measured using the Medical Research Council (MRC) grading system:
    MRC 0 = no function
    MRC 1 = flicker of contraction
    MRC 2 = function with gravity eliminated
    MRC 3 – anti-gravity function
    MRC 4 = function against gravity and resistance
    MRC 5 = normal power
    The first sign of reinnervation of a muscle is tenderness on muscle squeeze testing. Muscle bulk will take many months to recover and the ultimate strength will be lower than for an uninjured limb and there will be early fatigue with limited endurance.
    Failed reconstruction can be salvaged with revision grafting or distal nerve transfer. For sensory nerve restoration transfer of the superficial radial nerve dorsal branches can be transferred to the first webspace digital nerves (UDN thumb and RDN index). The 4th webspace nerve can also be transferred to the first webspace as an alternative strategy.
    There us a motor reconstruction that can be used to salvage the thenar function. The ADQ branch of the ulnar nerve deep motor branch can be transferred to the motor branch without a graft. There are other potential motor nerve donors including the EIP and EPB innervation from the posterior interosseous nerve.

    Recommended Reading

    The results of nerve graft reconstruction are variable. There are many factors influencing the outcome including the size of the nerve gap, the severity of the injury, adequacy of the debridement, the surgical bed, the time since injury, the type of nerve, the type of graft used and the distance from the nerve injury site to the targets.
    Mixed nerves perform wore than pure motor and in turn pure sensory nerves. The use of autologous nerve graft is the current gold standard treatment with processed nerve allograft performing comparably in sensory gaps up to 50mm. For mixed nerves, the evidence for allograft is less clear. For gaps that are longer than 50mm there appears to be a clear advantage in autologous sensory nerve grafts.
    Allograft has the advantage that it is not limited by host availability and there are no donor site complications.
    Allograft is expensive and not readily available in all territories, or within all healthcare facilities.
    The anticipated outcome from mixed nerve graft of 50mm is approximately 40% of patients will have a meaningful recovery of MRC grade 3 or greater motor function and Sensory MRC grade 3+ (enhanced level of sensory function) and 50-60% will have Sensory MRC grade 3 or above.
    Sensory recovery is measured using Semmes-`Weinstein monofilament pressurethrechold detection. Normal young adult perception is between 0.04g and 0.2g. Diminished sensation at 2g is an excellent outcome from nerve repair with some reaching 4g (protective sensation).
    Two point discrimination is used as a measure of sensory recovery, however therein a learning element and as such it is not as valid a measure os monofilaments. The 2PD can be measured as static or moving. Normal static 2PD (S2PD) in the thumb is approximately 5mm and moving 2PD (M2PD) is approximately 3mm.
    The results of Avance processed nerve allograft have been reviewed by the National Institute for Health and Care Excellence in the UK. Interventional Procedure Guidance (IPG 587) was released in 2017 and has reviewed all contemporaneous publications from the industry funder RANGER database as well as the outcome data prom independent centres and includes the results of RCTs in digital nerve reconstruction. To date there are no RCTs in Avance processed nerve allograft outcomes in mixed nerve reconstruction
    References:
    References:
    Rinker et al. Use of Processed Nerve Allografts to Repair Nerve Injuries Greater Than 25 mm in the Hand.Ann Plast Surg. 2017 Jun;78(6S Suppl 5):S292-S295
    The RANGER database is an industry registry of outcomes for Avance processed nerve allograft use in nerve gap reconstruction. A subset analysis for digital nerve injury with gaps of 25mm or greater demonstrated recovery to S3 level in 86% of repairs which compares favourably to historical data using autologous nerve graft (60-88%).The study to date demonstrated excellent safety data and an advantage of nerve allograft is the absence of potential donor site problems.


    Reference

    • orthoracle.com

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