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Targeted Muscle Reinnervation (TMR) of Superficial Radial Nerve using Axogen Avance processed nerve allograft

    Overview

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    The superficial radial nerve (SRN) is vulnerable to injury in the distal 1/3 of the forearm, wrist and hand. The main nerve trunk emerges from beneath the brachioradialis tendon and the divides into smaller branches that further divide as they pass across the anatomical snuff box to innervate the skin of the dorsum of the thumb, the first webspace and the dorsum of the index and middle fingers.
    Injured nerve branches may form neuromas, which are sensitive to local pressure or irritation from contact in this area and even the lightest tough from clothing may result in painful sensations. Avoidance is common and frequently superficial radial neuroma pain is intractable and resistant to neuromodulation therapy or surgical neuroma management.
    A historic mainstay of surgical management was the neuroma resection and relocation of the proximal stump to an intra-osseous drill hole. The aim was to minimise local irritation and should a recurrent neuroma form, this would be contained within the distal radial bone and therefore protected from further injury. Improved understanding of central neural mapping favours active reconstruction for neuromas, rather than simply resection and burying the stump in an intra-osseous tunnel. This can be achieved through reconstruction of the gap resulting from neuroma resection using either autologous nerve graft, or processed nerve allograft, which is my preference.
    The advantage of the allograft is the absence of donor site morbidity in patients with an existing pain driver and pain sensitisation. The technique is only possible though when there is a distal nerve stump to graft to. Successful axonal regeneration may reinnervate the denervated skin, provide physiologic central signalling from the peripheral and enable cortical down regulation of the previous peripheral pain source. Alternatively when a distal nerve stump is not available to reconstruct the divided nerve, the technique of targeted muscle reinnervation (TMR) allows active axonal regrowth along a grafted distal nerve branch to a muscle, and population of the intra-muscular neural plexus with the regenerated axons from the neuroma site to a deep location. During the regenerative phase, the central reprocessing of the afferent signalling reduces the pain perception intensity.
    The technique of TMR is proven in prevention of neuromas and phantom pain in primary amputation as well as in secondary intervention for neuroma pain after amputation. In the lower limb, TMR has been used primarily to redirect axons from a mixed motor-sensory nerve stump after transection to a motor branch in the vicinity of the amputation to goo effect. When there are no motor branches available, or the risk of muscle wasting and therefore prosthetic fitting or padding is a concern, then development of a reconstructive peripheral nerve interface (RPNI) may be preferred. Osteointegration may be used to improve prosthetic interface with the skeleton in cases with poor muscle bulk, in short stomps and in cases where there is neuroma pain from a traditional socket interface.
    Applying the technique of TMR to the management of superficial radial nerve (SRN) neuromas is an elegant method of achieving active neural regeneration in the absence of a good quality distal nerve stump, either as a primary procedure, or as a salvage after failed SRN neuroma surgery.

    The AXOGEN AVANCE processed nerve allograft is human nerve tissue that is processed to remove cellular material and neurotoxic glycoproteins. The nerve tissue is available in a number or lengths (15mm, 30mm, 50mm and 70mm) and diameters (1-2mm, 2-3mm, 3-4mm, 4-5mm). It is screened to reduce the risk of infection transmission and provided sterile and frozen.
    There is excellent safety data for use in nerve gap repair as well as efficacy data for digital nerve gap repair, including randomised controlled trial outcomes that are comparable with autologous graft. There also exists good data for non-digital sensory nerve gap repair. The evidence for use in motor and mixed nerve gap repair is more limited and data is collected in the RANGER database which reports on outcomes.
    Patients must be informed that it is derived from human nerve tissue.
    Readers will also find the following OrthOracle surgical techniques of interest;
    Digital nerve reconstruction with Axogen Avance processed nerve allograft
    Median nerve neurolysis, resection and reconstruction using Axogen AVANCE processed nerve allograft
    Radial nerve exploration and nerve grafting using autologous graft and AxoGen AVANCE nerve allograft .
    Radial nerve biopsy with Avance processed nerve allograft and Axoguard nerve protector reconstruction
    Dorsal cutaneous ulnar nerve reconstruction using Axogen Avance nerve allograft

    Indications

    Indications:
    The indications for TMR are an established symptomatic neuroma after previous surgery, or a nerve transection injury that does not have a suitable distal nerve stump available for active reconstruction with a nerve graft.
    In such cases, the superficial radial nerve(SRN) is often of sufficient length for direct transfer to the terminal anterior interosseous nerve stump to the pronator quadratus (PQ) muscle. There is no deficit of pronation when the proximal pronator teres is intact and functional. The SRN may be lengthened with processed nerve allograft when there is insufficient length for direct transfer. Allograft avoids the morbidity of autologous nerve graft in a sensitised individual, however, being derived from humans, it is not an acceptable to all patients.
    The PQ is an excellent target due to its deep location. Other symptomatic or potentially symptomatic cutaneous nerves may also be redirected to this muscle using this technique.
    Symptoms and examination:
    Symptomatic neuromas are associated with both contact “evoked” pain and “spontaneous” pain. The pain is characteristically neuropathic with sensations of tingling, burning or shooting often described by patients. There is usually extreme sensitivity to light touch with the hallmarks of dysaesthesia, allodynia and hyperalgesia. There is often avoidance behaviour. Patients will often have tried a number of different analgesic and neuromodulator medications to control their symptoms without long term benefit. There is usually notable apprehension when attempting to examine a patient with a cutaneous neuroma and they may flinch in anticipation of contact or draw their limb away. The examiner must be sensitive to the patient’s concerns and build up a rapport. Gently tapping from distal in a proximal direction along the course of the nerve under test may elicit a Tinel’s sign at the point of nerve irritation or neuroma. The Tinel’s sign, is positive when tingling or pins and needles is reported by the patient in the cutaneous territory of the nerve under test. The tingling sensations can be profound and prolonged and so to accurately determine the neuroma site, the examiner should avoid the main nerve trunk by commencing the examination distal to the neuroma and moving towards the neuroma and the nerve trunk.
    Investigations:
    A diagnostic peripheral nerve block under ultrasound guidance is recommended to determine that the symptomatic neuroma arises from the SRN. There is considerable overlap between the cutaneous territories of the SRN and the lateral cutaneous nerve of the forearm (LCNF) and often there are interconnecting branches in the periphery. The site of nerve block is therefore critical. Blocking in the proximal forearm risks overspill of local anaesthetic to the adjacent nerve. The SRN lies here deep to the brachioradialis muscle and the LCNF lies in the superficial fat adjacent to the cephalic vein. A better site for blockade of the radial nerve is in the upper arm as it emerges from the spiral groove at the lateral 1/3 of the humerus. A small volume of local anaesthetic is required because more then 5 mls may spread distally to the interval between the biceps and the brachialis and effect a block of the LCNF as it emerges lateral to the biceps tendon.
    An ultrasound of the site of suspected neuroma may be performed. In some patients the area is so sensitive that US must be reserved from after the nerve block. In other cases, MRI may be preferable to avoid the contact irritation of the neuroma.
    Conservative management:
    Sensitive neuromas may be initially managed with desensitisation and neuro-modulation physical therapy and oral neuromodulator medications. Central sensitisation pain may be optimised through mirror feedback therapy. Persistent neuropathic pain may require surgical management of the neuroma.
    Alternative operative management:
    The evidence in lower limb amputation as an intervention for neuroma and as prophylaxis during the index amputation period is good. Well constructed randomised controlled trials have been completed to support the emerging evidence base. The role of TMR in sensory nerve neuroma management is less well defined. The introduction of the technique to the “toolbox” for neuroma reconstruction is though justified given the variable results of the existing techniques. Simple neuroma resection, capping, burying to muscle or bone or “allografts to nowhere” are all described and have their proponents, however in a case with a distal nerve stump an active (reconstructive) technique is to be recommended, restoring the afferent pathway. When there is no distal nerve stump available for a graft, typically passive (ablative) procedures are performed, although using an active technique (graft to nowhere or TMR) provides an interval with reduced evoked pain and allow central down regulation of the pain pathways.
    Contraindication:
    Surgery is not recommended when there is no defined neuroma site, there is no good response to the diagnostic nerve block, there is poor soft tissue at the site of the planned surgery, when there is active infection, in cases where the patient does not comprehend the problem or is non-compliant with the management plan.

    Setup

    The site of the suspected neuroma is identified using the Tinel’s sign and then is marked with a permanent skin marker. The side for surgery is also marked after confirming with the patient. The patient should be consented for neuroma exploration, resection and targeted muscle reinnervation. Where possible this should include consent for using a processed nerve allograft as an interposition graft for a tension free co-aptation.
    Avance processed nerve allograft is supplied by Axogen Inc Florida, USA. It come prepared, packaged, sterilised and frozen in a number of lengths (15, 30, 50 and 70) and diameters (1-2, 2-3, 3-4 and 4-5mm). The possible sizes required should be ordered in advance and stored in the human tissue freezer at your hospital. In cases with infrequent use it is possible to receive a supply on dry ice that keeps the allograft frozen at or below the required transit and storage temperature for at least 72 hours. This method is subject to local arrangements with Axogen’s sales team or their distributor representatives in your territory.
    The anaesthesia usually consists of a regional anaesthetic block and the axillary level is appropriate for this surgery at the level of the distal forearm or wrist. The musculocutaneous nerve must be blocked due to the supply of the lateral cutaneous nerve of the forearm to the volar-radial distal forearm skin. General anaesthesia with local anaesthesia or adjunctive regional anaesthetic block is a suitable alternative. I consent patients for operative insertion of an indwelling local anaesthetic nerve catheter which can be used for an infusion or intermittent bolus of local anaesthetic in the peri-operative period for patients with severe neuropathic pain. The catheter, if used, is planned to be removed at 48 hours after the surgery.
    In theatre the WHO checklist is completed to confirm the patient, side, site of surgery, planned procedure and the necessary equipment. Operative and anaesthetic considerations are discussed. Intravenous antibiotics are administered prior to tourniquet elevation. Antibiotics are recommended when there is insertion of an avascular implant including processed nerve allograft.
    The limb is positioned on an arm table and a well-padded, appropriately sized pneumatic tourniquet is placed around the upper arm. The limb is exsanguinated using either an Esmarch bandage or a Rees-Davies pneumatic exsanguinator.
    The instrumentation needed for this procedure includes a basic hand tray with a medium self-retaining retractor (West or equivalent), Jamieson dissecting scissors, fine toothed Adson forceps, DeBakey non-toothed forceps, a Mixter or Gemini fine-tipped 90 degree clip, surgical silicone elastic loops, microsurgery background, microinstruments, 9’0 nylon sture and Tisseel (Baxter) fibrin glue.
    The limb is prepped and draped maintaining an aseptic field. Adjustable stools are useful for using loupe magnification or an operating microscope.

    Operation – 1

    The skin is incised along the radial border of the distal forearm.
    The arm is positioned and padded within a lead hand. A No.15 scalpel blade is used for the incision.

    The superficial radial nerve is identified, it lies at the dorsal edge of the brachioradialis tendonCare should be taken when dissecting through the subcutaneous fat due to the superficial location of the SRN and the LCNF branches. . In this case the SRN feels firm, thickened and is tethered distally.

    A Mixter is used to pass a surgical loop around the superficial radial nerve to facilitate retraction for neurolysis.The plane deep to the nerve is opened and the Mixter is passed deep to the nerve. A silicone elastic loop can be easily passed under the SRN using the Mixter to facilitate retrieval. The silicone sloop enables the nerve to be gently retracted for dissection from scar. This method minimises the instrument handling of the nerve, preventing further damage.

    In the volar aspect of the wound the terminal branches of the lateral cutaneous nerve of the forearm are identified.The LCNF branches are in close proximity on the volar aspect of the wound. The cutaneous territory overlaps with part of the SRN territory. In addition, anatomical studies and nerve block studies have shown branching interconnections between the SRN and the LCNF.

    A Mixter is used to pass a surgical loop under the lateral cutaneous nerve of the forearm.The LCNF branches are small and susceptible to traction injury. They must be protected during dissection.

    A surgical sloop is passed to the Mixter jaws.The sloop is retrieved in the Mixter jaws and passed deep to the LCNF branches.

    The superficial radial nerve is retracted to facilitate distal neurolysis.The sloop allows retraction with minimal handling of the nerve. The neurolysis enables mobilisation of the SRN from its bed. The SRN is lifted from the bed by the sloop. A communicating branch is seen between the SRN proximally and the LCNF distally.

    The SRN is tethered to the distal radius in the region of the base of the radial styloid.As the dissection continues distally, the SRN is seen to be adherent to the periosteum of the radial styloid in scar. The nerve has been previously transected for the management of the neuroma and implanted into a drill hole in the radial styloid.

    The SRN is mobilised and a neuroma is seen at the bone surface.The neuroma has reformed at the site of nerve transection and is tethered to the bone surface. This corresponded with the point of maximum Tinel’s sign on examination of the patient.

    Proximal dissection to define the branching anatomy of the SRN and the LCNF.There are many connections between the SRN and the LCNF described. In this case there are a leach of nerve branches between the two main named nerve trunks.

    The branching anatomy of the SRN and LCNF is demonstrated.

    Microsurgical background material is placed deep to the nerve branches, having been initially dissected and freed up.The patient had pain improvement after radial nerve block at the lateral humerus as part of the pre-operative evaluation. The second block of the musculocutaneous nerve resulted in a more convincing and complete loss of sensation and pain reduction. The reason could have been marginal sensitivity ion the territory of the LCNF adjacent to the territory supplied from the sectioned SRN or perhaps due to a afferent pathway that flows the course of the LCNF. Interestingly, the block of the SRN reduced pain partially but did not alter the residual abnormal sensation in the SRN territory on the dorsum of the first webspace. As a result of this the possibility of a residual SRN unsectioned branch or the sensitisation of the LCNF were considered. The aim of surgery was to remove any reduce sensitivity in the radial dorsal wrist and hand, eliminate a pain driver from the neuroma and to provide an active regenerative pathway for any sectioned nerve fibres through TMR.

    The branches of the LMNF and SRN are seen joining a common trunk.

    The volar skin incision is marked.
    The decision is made for proceeding to neuroma resection and TMR to the terminal PQ branch of the AIN.

    The volar incision is made on the ulnar side of the digital flexor tendons, lying between the FDS and the FCU.The arm is supinated and held in the lead hand to facilitate dissection and exposure of the AIN.

    The volar incision is made to the deep fascia.
    Small blood vessels are cauterised. Any small nerve branches should be identified and protected.

    The plane ulnar to the FDS muscle bellies is developed and the FDP tendons are exposed deep to the FDS.The FDS muscles are mobilised to the radial side and the ulnar neuromuscular bundle is protected in the ulnar aspect of the wound.

    The FDP tendons are exposed deep to the FDS.

    The deep dissection proceeds between the FCU and the FDP tendons.The FDP tendons can be mobilised as a group in a radial direction to allow exposure of the radius,ulna, interosseous membrane, AIN, anterior interosseous artery (AIA) and PQ beneath.

    The AIN and AIA can be seen on the interosseous membrane proximal to the pronator quadratus (PQ) muscle.

    The AIA and AIN are cleared from the interosseous membrane with careful blunt dissection.

    The AIN is mobilised and a Mixter is passed deep to the nerve and its branches proximal to the PQ, and then slooped

    A sloop is passed under the terminal AIN.
    This may be used to mobilise, neurolyse and retract the nerve during the subsequent dissection.

    A circumferential neurolysis is completed around the AIN.The nerve can be mobilised proximally so that there is sufficient length available for co-aptation to the proximal stump of the SRN and LCNF.


    In the dorsoradial wound, the superficial radial nerve is mobilised and then the neuroma can be resected.

    Operation – 2

    Returning to the dorsal exposure the neuroma is seen at the drill hole in the radius, and is released.The neuroma has formed at the distal SRN stump after the previous operation and can be seen tethered to the drill hole in the radial styloid. There may be further neuroma within the bone medullary cavity.

    The neuroma is released from the periosteum of the radial styloid.
    The SRN stump can then be reflected proximally. The branches to the LCNF can be seen and it is not possible to mobilise the SRN further proximally without intra-neural dissection of the LCNF branches from the SRN. There is a risk that this manoeuvre could result in scarring along otherwise intact fascicles and become a further source of pain.

    The neuroma has been mobilised and is ready for resection.

    The neuroma is resected from the end of the SRN.There is sufficient length of proximal SRN stump to mobilise to the AIN, however there is concern regarding potential pain origin from the LCNF, based on the pre-operative findings and the response to the serial local anaesthetic nerve blocks.

    The microsurgery background is used to protect the SRN stump and the LCNF branches during the development of a tunnel to the AIN.
    A small clip is used to hold the background material and gently retract the nerves.

    A plane is developed between the brachioradialis and the radial artery to pass the nerves deep to approximate to the AIN.Dissecting scissors are used to open and develop the plane.

    A tunnel is developed deep to the FDP tendons from the PQ, proximally and obliquely directed to the interval between the Br and the radial artery.A finger can be used to open up this plane and create a tunnel for the nerve.

    The deep part of the passage lies superficial to the AIN.
    A Langenbeck retractor is used to retract the flexor tendons and muscle bellies in a radial direction.

    A Mixter forceps is passed through the tunnel from deep ulnar and distal to superficial, radial and proximal.

    The Mixter tips are delivered to the interval created between the radial artery and the BR.

    The Mixter is passed through the interval.

    The Mixter is passed through the interval and a loop of silicone elastic material is introduced to the Mixter ready to be drawn into the tunnel.

    The loop is left long in the radial wound.

    The microsurgery background material is opened and the nerves inspected.
    A decision is made to resect and include the LCNF branches that are sensitive with the proximal SRN stump due to the local anatomy, the interconnections and the pre-operative findings. Sectioned together, there will be insufficient length for a direct tension free co-aptation to the distal AIN stump and so a processed nerve allograft is selected for bridging the gap.

    Avance processed nerve allograft of the required length is retrieved from the the human tissue freezer, defrosted and introduced into the surgical field.Avance processed nerve allograft is human nerve time harvested at the time of organ donation after death. The nerve tissue is screened for important infections and then is prepared with detergent washes and enzymes to deplete cellular material and provide a receptive environment for regenerating axons. The quality of the material is checked and then the nerve allograft is packaged in a number of lengths and diameters, frozen, irradiated and stored ready for distribution. The lengths available are 15mm, 30mm, 50mm and 70mm. The diameters are 1-2mm, 2-3mm, 3-4mm and 4-5mm. The processing and distribution is by Axogen Inc, Florida, USA. In some territories there is a distributer network. The Avance can be ordered in for a case or a number of sizes may be stored on site in a human tissue bank. The latter is the most convenient option for high use centres. The outer packaging should be checked for integrity and the unique identifying number recorded in the theatre implant register and the patient records. The inner packaging consists of a transparent tray. The lid should be hinged open on a flat surface and then saline placed in the tray to assist with defrosting. Typically this takes 5minutes with repeated irrigation with warm saline.

    The LCNF branches are trimmed and will be included in the TMR.The particular anatomy of the LCNF branches and the good response to local anaesthetic blockade of the musculocutaneous nerve mean that the nerve branches will be resected and they will be used in the TMR with the SRN proximal stump. The Avance processed allografts in the wound in preparation for co-aptation. The allograft selected for this case was a 70mm x 2-3mm due to the need to include both SRN and LCNF branches.

    The SRN is trimmed back to the same level as the LCNF branches.Trimming to the same level will allow a co-aptation to be readily performed at a single level.

    The proximal nerve stumps are prepared to proximal co-aptation to the allograft.Trimming the SRN back to the LCNF level means that a direct co-aptation TMR transfer to the terminal AIN cannot be performed. Interposition allograft will be required.

    There is a good size match for end-to-end co-aptation.
    The co-aptation site is supported on a microsurgical background in preparation for microsurgical suture.

    8’0 Ethilon suture is used to complete the proximal co-aptation, and sutured using microsurgical instrumentsEthilon interrupted sutures are placed evenly around the co-aptation site without distortion of the nerve ends. Fine sutures are used, typically of an 8’0 or 9’0 nylon.


    The Avance hasn’t been trimmed at this stage.

    The neurorraphy is completed.

    Tisseel fibrin glue is used to support the proximal co-aptation site.Fibrin glue provides some additional support to the suture site and can reduce the total number of sutures require. It can be used alone in a suture less repair, however the mechanical integrity is insufficient beyond 12 days to prevent repair site rupture and so if used in this way it should be reserved for situations where a detensioning interposition allograft or autograft can be used and there is little mobility of the reconstructed nerve. I use a few sutures plus tissue glue so that some early mobilisation can be performed.

    The microsurgery background is then wrapped around the proximal co-aptation site and Tisseel, which allows a well-conformed layer of enclosing Tisseel around the whole circumference of the co-aptationThis even layer provides greater resistance to rupture of the co-aptation site.

    The proximal co-aptation is completed and the Tisseel layer is inspected for completeness.
    The nerve co-aptation is well aligned and supported by Tisseel. This is adequate now for handling and passage through the tunnel to the terminal AIN at the PQ muscle.

    Operation – 3

    The allograft is passed through the silicone elastic loop, which is then passed through the tunnelThe nerve should be handled carefully with either microsurgical forceps or De Bakey forceps picking up the epineurium alone. The nerve allograft contains delicate endometrial tubes that are vulnerable to distortion and injury with any compression.

    The allograft is delicately held in microsurgical forceps as the silicone loop is retrieved through the tunnel.
    Great care should be taken too ensure that the co-aptation site isn’t damaged during this process.

    The co-aptation site is supported to ensure that there is no traction across it.
    The allograft is delivered to the tunnel and the co-aptation site is protected.

    The allograft is passed into the tunnel slowly to prevent damage to the nerve.

    The co-aptation site is lying at the mouth of the tunnel.

    The allograft is in position and the proximal co-aptation is deep to the radial vessels.The silicone elastic loop is retrieved through the volar incision delivering the allograft to the deep tissue layer. The remaining silicone loop is around the AIN which hasn’t been divided yet.

    The allograft is safely delivered to the AIN bed.
    The nerve allograft now lies in the deep pocket between the digital flexor tendons and the PQ muscle.

    The AIN is mobilised before transection proximally.The AIN supplies the FDP to the Index and Middle fingers, the FPL and finally the PQ. The AIN is sectioned proximally for sufficient length for the TMR transfer, but distal to the FPL innervation. PQ function will be lost, however the residual function of the Pronator Teres will maintain forearm pronation.
    The neurolysis should be completed prior to transection, handling the AIN gently using only the silicone loop for gentle traction.

    The co-aptation between the distal end of the allograft and the cut end of the distal AIN stump is performed.There is is size mismatch. The co-aptation is sutured using 9’0 Ethilon and an operating microscope.

    The neurorraphy is completed using micro instruments.
    There is a redundant loop of allograft proximal to the neurorraphy.

    Tisseel to used to complete the distal co-aptation.The fibrin glue provides additional support to the distal co-aptation. Tisseel is delivered using a syringe and mixing cannula. The microsurgical background is used to temporarily wrap the co-aptation to achieve a consistent and complete layer around the ends of the nerve.

    The Tisseel sets in a few seconds and the microsurgical background material can then be removed.
    Gentle pressure is applied to the background material to the side of the nerve which lies in the midpoint along the “spine” of the folded material.

    The completed distal co-aptation with Tiseel wrap is lying loosely in the deep layers.
    There is no tension across the nerve co-aptation site. `the TMR has redirected the fibres from the proximal SRN and LCNF branches, through an Avance processed nerve allograft to the terminal AIN to the PQ. The regenerating axons will have a long length of allograft to repopulate and then can finally grow deep into the intramuscular neural plexus of the PQ. The TMR technique is described predominantly for mixed nerves, however the technique can be valuable in the management of sensory neuromas.

    Finally the distance of the neurorraphy from a fixed boney landmark should be noted to enable accurate monitoring of neural regeneration in the post-operative period.During follow up the Tinel’s sign progression can be monitored to ensure that the nerve regenerates through the proximal co-aptation, the allograft and to the PQ. Tinel’s sign should move distally as the nerve regenerates. Using a boney landmark allows accurate measurements of the rate of progression at sequential outpatient clinic reviews.

    The wounds are closed with subcuticular absorbable sutures.

    The completed wound closure.

    The wounds are closed and ready for dressings.Note that there is a third incision along the dorsum of the thumb MCPJ. The original nerve injury was associated with arthrodesis of the MCPJ for chronic instability. The Kirschner wires were causing skin irritation and so these were removed during this procedure.

    Steristrips are applied to the closed wounds.

    Occlusive dressings are applied to the wounds.

    A bulky dressing with wool and ripe bandaging is applied to the limb.The fingers should be free to move. The bulky dressing will limit wrist movement. Due to the tension free TMR using allograft with redundancy. there is no need to use a plaster to immobilise the limb in the post-operative period.
    An indwelling nerve catheter can be placed proximal to the proximal co-aptation for post-operative local anaesthetic infusion and intermittent boluses.

    Post Operative

    The patient is advise to keep the limb elevated in a Bradford sling for 72 hours after surgery. the fingers can be mobilised and used functionally as soon as the regional block is worn off. The surgery can be completed as a day case, however in patients with severe neuropathic pain, using an indwelling nerve catheter with a local anaesthetic infusion can be helpful and is such cases I would advocate an overnight stay in hospital to ensure that there is no rebound uncontrollable neuropathic pain when the regional anaesthesia wears off.
    Dressings may be reduced after 5 days and the wound can be allowed to get wet after 10 days. Scar massage can be commenced from 2 weeks.
    The patient is advised to continue with their usual pain medications and any neuromodulator agents during the peri-operative period. The patients is advised to wait until the 6 week post-operative appointment check before commencing weaning of neuromodulators. The reducing regimen should be over 3 to 6 months.
    During the post-operative period the Tinel’s sign may be monitored to demonstrate axon regeneration through the proximal co-aptation site.
    The process of regeneration into the allograft, along the allograft and into the PQ will take between 3 and 6 months. During this time neuro-rehabilitative strategies including mirror therapy may be employed to assist in controlling the central sensitisation component of the neuropathic pain syndrome.

    Recommended Reading

    TMR is a relatively new application of nerve transfer surgery aimed at reducing neuropathic pain from neuromas and the phantom limb pain experienced following amputation.
    The evidence in lower limb amputation as an intervention for neuroma and as prophylaxis during the index amputation period is good. Well constructed randomised controlled trials have been completed to support the emerging evidence base. The role of TMR in sensory nerve neuroma management is less well defined. The introduction of the technique to the “toolbox” for neuroma reconstruction is though justified given the variable results of the existing techniques. Simple neuroma resection, capping, burying to muscle or bone or “allografts to nowhere” are all described and have their proponents, however in a case with a distal nerve stump an active (reconstructive) technique is to be recommended, restoring the afferent pathway. When there is no distal nerve stump available for a graft, typically passive (ablative) procedures are performed, although using an active technique (graft to nowhere or TMR) provides an interval with reduced evoked pain and allow central down regulation of the pain pathways.
    References:
    Arnold DMJ, Wilkens SC, Coert JH, Chen NC, Ducic I, Eberlin KR. Diagnostic Criteria for Symptomatic Neuroma. Ann Plast Surg. 2019 Apr;82(4):420-427. doi: 10.1097/SAP.0000000000001796. Erratum in: Ann Plast Surg. 2019 Jul;83(1):120. PubMed PMID: 30855369
    This paper describes the diagnostic criteria for defining a neuroma. In a case with a history consistent with a nerve injury, poor recovery, a positive Tinel’s sign and good pain response to a local anaesthetic block, then a neuroma may be diagnoses. The neuroma may be confirmed with US or MRI imaging.
    Eberlin KR, Ducic I. Surgical Algorithm for Neuroma Management: A Changing Treatment Paradigm. Plast Reconstr Surg Glob Open. 2018 Oct 16;6(10):e1952. doi: 10.1097/GOX.0000000000001952. eCollection 2018 Oct. PubMed PMID: 30534497; PubMed Central PMCID: PMC6250458
    This paper reports the different methods for surgical management of neuromas and classifies procedures as ablative / passive or reconstructive / active.The techniques of TMR and RPNI are discussed in the active category alongside grafts to nowehere, graft to distal stump and loop Centro-central anastomosis.
    Salminger S, Sturma A, Roche AD, Mayer JA, Gstoettner C, Aszmann OC. Outcomes, Challenges, and Pitfalls after Targeted Muscle Reinnervation in High-Level Amputees: Is It Worth the Effort? Plast Reconstr Surg. 2019 Dec;144(6):1037e-1043e. doi: 10.1097/PRS.0000000000006277. PubMed PMID: 31764652
    30 patients with upper limb amputation were treated, 19 for improved prosthetic control and 11 for neuroma pain management over a 5 year period. All achieved a myoelectric signal and in the 10 at final follow up analysis there was improved function. There were cases of abandonment of prosthetics after otherwise successful surgery and the conclusion was that there would need to be improvements in the biotechnological interface to improve adoption and long term use of advanced prosthetics in the future.
    Chappell AG, Jordan SW, Dumanian GA. Targeted Muscle Reinnervation for Treatment of Neuropathic Pain. Clin Plast Surg. 2020 Apr;47(2):285-293. doi: 10.1016/j.cps.2020.01.002. Epub 2020 Feb 5. Review. PubMed PMID: 32115054
    This review reports that the development of an active regeneration through TMR is superior to direct muscle implantation in the management of nerve pain.
    Fracol ME, Dumanian GA, Janes LE, Bai J, Ko JH. Management of Sural Nerve Neuromas with Targeted Muscle Reinnervation. Plast Reconstr Surg Glob Open. 2020 Jan 17;8(1):e2545. doi: 10.1097/GOX.0000000000002545. eCollection 2020 Jan. PubMed PMID: 32095388; PubMed Central PMCID: PMC7015593
    This paper explores the concept of sensory only TMR for the prevention or management of neuroma pain. The technique ds=escribes direct transfer of the rural nerve proximal stump to the lateral gastrocnemius branch to direct the regenerating sensory axons to deeper tissues, away from the skin.
    Janes LE, Fracol ME, Ko JH, Dumanian GA. Management of Unreconstructable Saphenous Nerve Injury with Targeted Muscle Reinnervation. Plast Reconstr Surg Glob Open. 2020 Jan 17;8(1):e2383. doi: 10.1097/GOX.0000000000002383. eCollection 2020 Jan. PubMed PMID: 32095383; PubMed Central PMCID: PMC7015600
    This clinical series of 18 cases reports saphenous branch transfer to adjacent motor branches. Two patients had recurrent pain, 6 were lost to follow-up and 10 noted pain resolution after the TMR.
    Alexander JH, Jordan SW, West JM, Compston A, Fugitt J, Bowen JB, Dumanian GA, Pollock R, Mayerson JL, Scharschmidt TJ, Valerio IL. Targeted muscle reinnervation in oncologic amputees: Early experience of a novel institutional protocol. J Surg Oncol. 2019 Sep;120(3):348-358. doi: 10.1002/jso.25586. Epub 2019 Jun 13. PubMed PMID: 31197851
    This is a cohort study of 31 patients having primary TMR at the time of oncologic amputations. The authors report fewer neuromas and less neuroma pain intensity than in a cross-section sample of oncological amputees treated elsewhere.
    Valerio IL, Dumanian GA, Jordan SW, Mioton LM, Bowen JB, West JM, Porter K, Ko JH, Souza JM, Potter BK. Preemptive Treatment of Phantom and Residual Limb Pain with Targeted Muscle Reinnervation at the Time of Major Limb Amputation. J Am Coll Surg. 2019 Mar;228(3):217-226. doi: 10.1016/j.jamcollsurg.2018.12.015. Epub 2019 Jan 8. PubMed PMID: 30634038
    This is a multi-institutional cohort study of 51 patients undergoing TMR at the time of major limb amputation compared to 438 major limb amputees. A number of measures were performed including a PROMIS score and a numerical rating scale. The interventional cohort experiences less phantom limb pain and less residual limb pain. The authors recommend TMR at the time of amputation to reduce limb pain and phantom pain.
    Dumanian GA, Potter BK, Mioton LM, Ko JH, Cheesborough JE, Souza JM, Ertl WJ, Tintle SM, Nanos GP, Valerio IL, Kuiken TA, Apkarian AV, Porter K, Jordan SW. Targeted Muscle Reinnervation Treats Neuroma and Phantom Pain in Major Limb Amputees: A Randomized Clinical Trial. Ann Surg. 2019 Aug;270(2):238-246. doi: 10.1097/SLA.0000000000003088. PubMed PMID: 30371518
    This is an RCT and 28 patients with limb pain after amputation were randomised to either standard care or TMR. There were 3 cross-over patients to the TMR arm. The authors recommend TMR for the management of residual limb pain.
    Bowen JB, Ruter D, Wee C, West J, Valerio IL. Targeted Muscle Reinnervation Technique in Below-Knee Amputation. Plast Reconstr Surg. 2019 Jan;143(1):309-312. doi: 10.1097/PRS.0000000000005133. PubMed PMID: 30589808
    This study reports on the use of TMR in the management of below knee amputation patients and notes that untreated there is a rate of 25% residual limb pain. All patients report phantom pain at 1 month, however by 3 months, all patients had phantom limb pain resolution. The patients were followed to one year and the paper supports extending the use of TMR to the below knee amputation patient.

    Reference

    • orthoracle.com

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