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Median nerve- Acute repair of laceration

    Overview

    Learn the Median nerve: Acute repair of laceration 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: Acute repair of laceration surgical procedure.
    Primary repair of an acute peripheral nerve laceration is a common procedure, performed by orthopaedic surgeons, plastic surgeons and others. A good outcome depends upon thorough careful examination and diagnosis followed by an early exploration and repair using a microsurgical technique.
    Following a sharp laceration to any peripheral nerve, there is complete transection of axons. Axons within the distal stump of the nerve undergo a process termed Wallerian degeneration. This involves axonal degradation and loss of neuromuscular conduction.
    The current standard surgical treatment is an epineurial repair with microsurgical techniques, some of which are demonstrated in this section. The aim of nerve repair is to realign the proximal and distal stumps to allow axons to regenerate into the distal stump and provide reinnervation.
    Often a primary repair cannot be performed without excessive tension, either due to necessary debridement of the nerve ends, a delayed repair in a fibrotic bed or local anatomical factors.
    In these cases an interpositional nerve autograft can be used to bridge the gap. More recently other technologies such as nerve conduits, and processed nerve allograft may be used to bridge small gaps and detension the repair site. All of these techniques are described elsewhere on Orthoracle.
    Cabled autograft reconstruction of median nerve
    Allograft reconstruction of a median nerve
    Allograft reconstruction
    Conduit assisted repair
    The following case illustrates the technique used in the direct repair of a partial median nerve division in the forearm.

    Indications

    INDICATIONS
    Any penetrating injury around the hand or wrist with loss of motor or sensory function carries a high likelihood of nerve injury. At our institution these injuries are surgically explored within 48 hours. Any nerve laceration is primarily repaired with an epineurial repair technique. Partial lacerations are similarly repaired, ensuring that the fascicles are aligned correctly.
    SYMPTOMS & EXAMINATION
    In this particular case the patient complained of weakness of thumb opposition and a loss of sensation in the tips of the thumb, index and middle fingers. There was a positive Tinel’s test when tapping over the median nerve at the level of the laceration which reproduced pain radiating into the radial sided digits.
    The patient may also complain of neuropathic pain and on examination there may be dry skin, and erythema in the distribution of the nerve due to loss of sudomotor function.
    The classification of nerve injuries helps to understand the underlying pathology, management and prognosis.
    Seddon’s classification described the three categories of nerve injury and has prognostic relevance. The three categories are:
    Neurapraxia: Compression, traction or local ischaemia with structural continuity of the nerve mainatained.
    Axonotmesis : Division of axons but other layers of the nerve left intact.
    Neurotmesis : Transection of all layers of the nerve. The severest grade of injury.
    Sunderland later added further grades of axonotmesis. Grade 3 represents damage to the endoneurium and grade 4, damage to the perineurium.
    A Sunderland grade 5 represents a neurotmesis with epineurial discontinuity.
    Surgeons treating nerve injury recognise that many continuity lesions are mixed nerve injuries with different components of the same nerve demonstrating different classes.
    Mackinnon has added a Grade 6 to formally include these injuries.
    IMAGING AND NEUROPHYSIOLOGY
    Ultrasound or MRI can confirm discontinuity of the nerve but is not routinely used.
    Neurophysiology in the early post injury phase is not especially useful either and becomes more valuable after a few weeks when dennervation changes following Wallerian degeneration become established.
    In the acute setting further investigations tend to cause unnecessary delay when the injury at hand is an open wound with neurological dysfucntion that will require exploration as soon as feasible.
    ALTERNATIVE OPERATIVE TREATMENT
    Alternative operative treatmemnt is sought when primary repair without tension is not possible. Tension at the suture line causes local ischaemia which negatively impacts regeneration. Detensioning can be perfomed by using a reversed autograft in a technique described elsewhere on orthoracle. Avoidance of the donor site morbidity and extra operative time associated with the use of autograft has lead some surgeons to use allograft over relatively short gaps. Whilst these allografts are safe to use, their efficacy for large diameter mixed motor nerves is yet to be fully elucidated. In our practice allograft has been used to avoid donor site problems, particularly in sensitised patients. They allow regeneration to occur but this tends to be rather slower than across a similar length and diameter of autograft. Careful case selection, thorough consent and follow up as part of an audit or established research project is standard practice when using nerve allograft.
    In partial nerve lacerations the intact portion of the nerve is usually assumed to be unscathed, although this may not be the case in high energy injuries where a lower grade of injury may indeed have occurred where there is anatomical continuity.
    Interpositional grafting is occasionally required in a partial injury where there is gapping, for example after debridement.
    NON-OPERATIVE MANAGEMENT
    There are no non-operative alternatives to primary nerve repair for a sharp laceration at the wrist.
    CONTRAINDICATIONS
    Contraindications to primary nerve repair are the presence of active infection or a poor surgical environment such as a complex surgical without adequate soft tissue cover over the nerve.
    Excessive tension across the nerve repair is also a relative contraindication to direct repair and detensioning with the techniques outlined above may therefore be indicted.

    Setup

    Surgery is performed in a day case setting under regional anaesthesia. This involves placement of a brachial plexus block under ultrasound guidance.
    Occasionally a supplemental subfascial block is required in the medial upper arm to provide anaesthetic cover under the tourniquet. The tourniquet was applied in this case but not used.
    A standard operating arm table is used to support the arm.
    Bipolar diathermy, good lighting, micro-instruments, loupe magnification and an operating microscope are all essential tools.
    A dose of pre-procedure antibiotics are administered in line with the hospitals protocol.

    Operation – 1

    A preoperative examination of the patient revealed some loss of sensation in the thumb, index and middle fingers as well as loss of motor power in the thenar muscle group.
    Sensation in the palmar cutaneous branch of the median nerve territory was normal.
    All of the flexor tendons for the wrist and digits were examined and found to be intact.
    This is corroborated by the maintainance of the digital cascade seen here.

    The laceration is examined to plan the approachThe orientation of the laceration within the deeper layers is an important consideration in penetrating injuries. Passing a blunt instrument such as the tip of a closed pair of tenotomy scissors into the laceration reveals that it passses through the deep fascia in a radial and slightly proximal direction. There is no deep breech in an ulnar or more distal direction.

    This incision is planned in line with the median nerve allowing longitudinal exposure of the nerveThis is in accordance with the clinical findings as well as the direction of the original penetrating injury.
    Here the history and examination make it clear that the median nerve must be explored, and that any other injuries will be best accessed via an approach that lies radial to the wound, since that is the direction of the original penetration.

    The skin is incised connecting the original traumatic laceration with the extension

    Skin hooks are used to lift the corner of the proximal skin flap. Full thickness flaps are raised.
    Often, the very edges of the skin laceration must be excised as part of the initial debridement of the wound. Here the original injury was made by a sharp clean instrument and the edges are clean and bleeding normally, and so this is not deemed necessary.

    The deep fascia is incised in line with the skin incisionThe breech in the deep fascia can be seen in the distal part of the wound.
    This opening is extended to visualise the zone of injury.
    The preferred technique is to identify the nerve outside of the zone of injury and expose it in the direction of the zone of injury thereafter.
    The deep fascia is incised sharply along the ulnar border of the palmaris longus tendon.
    The palmar cutaneous branch of the median nerve lies close to this tendon but lies along its radial border between it and the tendon of flexor carpi radialis.

    The median nerve is inspected for signs of injuryA transverse breech can be seen in the epineruim of the median nerve.
    It is already clear that the injury is not a complete division of the nerve wich usually results in retraction of the nerve ends due to a physical property known as tensegrityThe nerve is furhter

    Dissection proceeds proximally along the length of the nerve in order to expose non injured nerve tissueThe soft tissue overlying the median nerve is divided in line with the nerve. This is done by gentle blunt dissection with a pair of tenotomy scissors.

    The exposure may be improved by splitting the thick deep fascia proximally. One may also retract the palmaris longus tendon radially and suture the ulnar sided skin flaps to aid retraction.

    The distal exposure is improved by dividing the deep fascia under the distal skin flap.
    A – Palmaris longus tendon
    B – Median nerve

    The palmar cutaneous branch of the median nerve is identified and protected in a rubber sloopLifting the palmaris longus with a Raglan retractor allows visusalisation of the nerve just radial to this tendon. A mixter is used to pass a sloop around this nerve.

    This nerve supplies the skin over the volar surface of the proximal palm. It arises from the median nerve trunk 6-8 cm proximal to the wrist crease and runs in between the FCR and palmaris longus tendons towards the palm. In the palm it divides into a lateral and medial branch communicating with branches of the lateral cutaneous nerve of the forearm and the volar cutaneous branches of the ulnar nerve.

    A mixter is passed around the median nerve just proximal to the injuryOnce the median nerve epineurium is dissected free from its enveloping layer it is circumferentially exposed and a mixter is passed underneath it.
    A sloop may then be passed around it to allow safe handling and retraction of the nerve during mobilisation and repair.
    The mixter must not be opened and then closed whilst its tip lies behind the nerve since this risks catching the epineurium or a side branch of the nerve in the jaws of the instrument.

    A rubber sloop is passed behind the nerve.

    The sloop is now used to gently lift the median nerve allowing exposure of its deep surface and evaluation of the extent of injury.

    Microsurgical instruments are used to continue the fine dissection of the nerveHere the straight micro-scissors and jewellers forceps are used to improve the exposure of the nerve with some fine dissection to expose the epineurium just proximal and distal to the laceration.
    The use of microsurgical instruments, under either loop magnification or microscope, allows the surgeon to treat the nerve with delicacy. It also allows identification of non-viable tissue. This can be resected where necessary using the microsurgical scissors.

    The assistant uses the rubber sloop to retract the nerve whilst the microforceps and curved microscissors are use to dissect the deep surface of the injured nerve.

    With the nerve mobilised, a sloop may be passed distal to the zone of injury for ease of handling, in preparation for the repair.

    The haematoma and any debris within the laceration are now washed out with normal salineThis allows the haematoma within the endoneurium to be washed out and allows a better appreciation of the extent of the injury.
    Here it becomes clear that more than 75% of the cross sectional area of the nerve has been divided and that the epineurial breech extends around the nerve involving about 60% of its circumference.
    With the tourniquet deflated one can see that the nerve ends are well perfused with bleeding through endoneurial vessels at both ends of the nerve. No further debridement of the nerve ends is necessary.

    Background material is placed behind the nerve to improve visualisation of both the nerve and the microsutures under microscope magnificationIf tissue glue is to be used the background helps contain the glue around the repair site.
    Some surgeons advocate use of dampened surgical gauze behind the nerve to act as both a background and to help rotate the nerve along its axis. This allows one to access the back wall of the nerve with minimal assistance.

    The microscope is now brought into the field.
    This step requires removal of the surgeons loupes, positioning of the scope alongside the arm table and scrub nurse as well as setting up the surgeons eye pieces for interpupillary distance, correction of any refractive error, and the correct focal length and zoom settings.
    Much of this can be done pre-operatively as part of the planning process for the procedure ensuring that this step is as seamless as possible and that the microsurgical part of the operation can commence without any delay or difficulty.

    The nerve ends are orientated using superficical markings such as epineurial vessels to line up the fascicles.In a partial nerve injury the orientation of the nerve ends is not usually in doubt. This contrasts with complete division with retracted nerve ends, where correctly aligning the two nerve ends can be more difficult.
    Superficial vessels on the epineurium are very helpful in confirming correct alignment.
    These are marked A
    Knowing the topograpical arrangement of the main fascicle groups within the nerve at the location of injury can also be helpful.
    In complete injuries with retracted nerve ends, the two ends are difficult to bring together. In such scenarios two epineurial sutures of either 8/0 nylon or 6/0 prolene placed at the equator of the nerve can serve to hold the nerve ends together whilst the finer sutures are placed.

    Microsutures are placed into the epineurium using 9/0 nylon and a microsurgical techniqueHere the first suture is placed into the distal nerve. The suture should pass through the epineurium without breaching the deeper layers of the nerve.

    As the knot is secured, the epineurium is seen to come together, lining up the fascicles beneath so that they are facing one another.
    Unlike a microvascular repair, where complete apposition of the tissues is required, here a tiny gap between the fascicles is preferable to a tight contact.
    Results of nerve repair suggest that a small gap of a few mm will be filled by a fibrin matrix across which Schwann cells and regenerating axons can migrate. On the contrary, fascicle overlap due to bunched or poorly aligned repairs is detrimental to successful nerve regeneration.

    The minimum number of sutures to align the nerve ends and prevent gapping are placed.Three epineurial sutures are required here to bring the nerve together and match the intact part of the nerve.
    The number of sutures placed should be no more than the minimum required to ensure correct coaptation.

    Operation – 2

    Gentle passive flexion and extension of the wrist shows that the repair is robust enough to withstand some motion during the early healing period.
    There appears to be no excessive tension across the repair.

    The wound is washed out. The background material and sloops are removed.In this case the tourniquet was not inflated but if a tourniquet has been used it is released and any bleeding areas attended to.

    Deep dermal sutures of 4/0 monocryl are placed to align the flaps correctly

    The skin closure is completed using interrupted sutures with 4/0 Vicryl Rapide.

    A non adherent dressing such as Mepitel is applied to the wound. This is covered by a layer of blue gauze.

    The wound is wrapped in a layer of sterile wool and crepe.Immobilisation is not required unless there are concerns about a fragile nerve repair that may fail under normal excursion of the wrist or if there was a tendon repair or fracture treated at the same time.

    A crepe dressing applies some gentle pressure over the wool.
    The arm is then placed into a Bradford sling for elevation of the wound and for safely immobilising the arm following regional block.
    This bulky dressing largely limits movement for the forst 7-10 days and so a plaster is not applied to immobilise the limb. If it is felt that any wrist movement would compromise the integrity of the repair a plaster of Paris slab is applied to immobilise the wrist.

    Post Operative

    The patient is allowed to return home the same day with oral analgesia (cocodamol 30/500mg prn)
    The patient is advised to commence gentle finger movement within the first 48 – 72 hours as pain allows.
    A review in the dressing clinic is arranged at 1 week post procedure. The dressings are reduced and formal hand therapy is commenced. This involves strengthening and desensitisation as well as nerve gliding excercises. The sutures are absorbable and do need need formal removal.
    The patient is reviewed at 6 weeks. The distal most Tinels sign along the course of the nerve is mapped out and recorded. It should demonstrate evidence of regeneration of 1-3mm per day since the time of surgical repair.
    Subsequent rehabilitation should continue for a year to 18 months until gains in sensation and motor strength have plateaued.
    Any nerve repair may be complicated by a repair site neuroma. If this becomes troublesome, or regeneration remains poor, re-exploration and potential nerve reconstruction should be discussed with the patient. If motor or sensory recovery is limited, further reconstructive options such as nerve or tendon transfers should be discussed with the patient and offered in a timely manner if appropriate.

    Recommended Reading

    1. Yi C, Dahlin LB. Impaired nerve regeneration and Schwann cell activation after repair with tension. Neuroreport 2010;21:958-962.
    One of numerous studies demonstrating the deliterious effect of tension on nerve regeneration. Minor tension impaired axonal outgrowth by 29%
    2. Boeckstyns ME, Sørensen AI, Viñeta JF, et al.. Collagen conduit versus microsurgical neurorrhaphy: 2-year follow-up of a prospective, blinded clinical and electrophysiological multicenter randomized, controlled trial. J Hand Surg Am 2013;38:2405-2411.
    A key study comparing the results of direct nerve coaptation with conduit assisted repair across small gaps of 6mm or less. The study demonstrated equivalent outcomes at 24 months in mixed motor nerves
    3. Birch R, Raji AR. Repair of median and ulnar nerves. Primary suture is best. J Bone Joint Surg Br. 1991;73(1):154-157.
    An old series demonstrating the best results were in young patients with distal injuries followed by early, primary repair.

    Reference

    • orthoracle.com

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