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Carpal tunnel decompression

    Overview

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    Median nerve compression at the wrist resulting in Carpal tunnel syndrome is the most common peripheral nerve entrapment neuropathy. Patients will report tingling and numbness in the thumb index and middle fingers, difficulty manipulating small objects, aching around the wrist and a tendency to drop things. Night time symptoms of tingling disturb sleep and frequently numbness persists on waking. The loss of fine motor control is due to loss of sensory feedback as well as median-innervated intrinsic muscle weakness and the loss of thumb opposition. Clinical examination will confirm the diagnosis and neurophysiological tests may be used to confirm the diagnosis, provide a severity of grading or help in diagnosis in challenging or atypical presentation.
    Open surgical decompression of the Carpal tunnel remains the gold standard although mini-open and endoscopic Carpal tunnel decompression have become popular in an attempt to reduce scar sensitivity following surgery and shorten return to work. Limited exposure techniques convey a higher risk of iatrogenic nerve injury. I use a traditional open approach in my practice.
    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
    Median nerve neurolysis, resection and reconstruction using Axogen AVANCE processed nerve allograft

    Indications

    Indications:
    Carpal tunnel decompression is indicated for patients with intrusive symptoms of at least 3 months duration who have trialled a course of conservative management including use of night time extension wrist splints and steroid injection. For patients with longstanding symptoms with sensory loss or motor wasting surgical treatment is advised to prevent further loss of function.
    Symptoms and examination:
    Patients with carpal tunnel syndrome report tingling and numbness in the thumb, index and middle fingers, weakness in the thumb with loss of dexterity and aching in the wrist and arm. The aim of the examination should be to exclude other pathology and confirm the diagnosis of carpal tunnel syndrome. Special tests are designed to provoke symptoms and confirm the diagnosis.
    The cervical spine should be examined for range of motion and root irritation. C6 sensory radiculopathy causes sensory disturbance in the radial hand although the sensory dysfunction includes the dorsum of the hand and the radial forearm.
    Proximal entrapment at the lacertus fibrosis, the pronator teres or the flexor digitorum superficialis tendinous arch are less common than carpal tunnel compression and are associated with additional sensory alteration in the palmar cutaneous branch of the median nerve territory (over the thenar eminence) as well as weakness in the median innervated long flexors (FDP to the radial 2 digits, FDS and FPL) plus the median innervated intrinsic muscles typical of distal entrapment neuropathy at the carpal tunnel.
    Phalen’s test, direct compression test and a positive Tinel’s sign at the carpal tunnel are all suggestive of entrapment neuropathy at the level of the carpal tunnel. The thenar muscles should be examined for wasting or weakness and an assessment should be made of opposition function which is compromised in severe carpal tunnel due to reduced palmar abduction and pronation in the thumb.
    Quantitative sensory testing can be performed with Semmes-Weinstein or West monofilament pressure threshold detection. 2 point discrimination and moving 2 point discrimination can be used to assess innervation density.
    Investigations:
    Endocrine abnormalities should be considered as secondary causes of carpal tunnel syndrome or as causes of peripheral neuropathy which may cause diagnostic confusion.
    The use of neurophysiological studies to confirm the diagnosis is not mandatory, however these studies are useful in atypical presentations, co-existent pathology, severe lesions and previous failed surgery. Typically an increase in latency above 4msecs and a slowing of sensory conduction velocity below 45m/sec are consistent with an electrophysiological diagnosis of carpal tunnel syndrome.
    Jeremy Bland (Muscle Nerve 2000 Aug;23(8):1280-3) has validated a 7 grade neurophysiological scale for the diagnosis of carpal tunnel syndrome:
    Normal (grade 0)
    Very mild (grade 1) – CTS demonstrable only with most sensitive tests
    Mild (grade 2) – sensory nerve conduction velocity slow on finger and wrist measurement; normal terminal motor latency
    Moderate (grade 3) – sensory potential preserved with motor slowing; distal motor latency to abductor pollicis brevis (APB) < 6.5 ms
    Severe (grade 4) – sensory potentials absent but motor response preserved; distal motor latency to APB < 6. 5 ms;
    Very severe (grade 5) – terminal latency to APB > 6.5 ms;
    Extremely severe (grade 6) – sensory and motor potentials effectively unrecordable (surface motor potential from APB < 0.2 mV amplitude).
    In a clinical case series outcomes were less predictable in grade 1 and grades 5 and 6 disease reflecting diagnostic errors and severe nerve pathology respectively.
    Imaging of the nerve is not indicated unless there is a suspicion of a space occupying lesion within the carpal tunnel causing extrinsic compression or the possibility of an intrinsic peripheral nerve sheath tumour. Ultrasound is a useful imaging modality and an assessment of nerve cross-section area as well as nerve glide during wrist and finger movement can provide useful information on compression sites and tether – particularly in revision surgery cases.
    Non-operative management:
    Carpal tunnel syndrome is common and the prevalence is approximately 1:1000 adults. Activity modification, non-steroidal anti-inflammatory medications, wrist splintage and steroid injection may all provide symptomatic relief. Persistent or recurrent cases may be offered surgery but a trial of conservative measures for 3 months should be considered primarily unless there is established motor dysfunction at presentation.
    Alternative operative management and contraindications:
    A number of different surgical techniques have been described to reduce the complications of scar pain and pillar pain at the base of the hand. Short incision surgery with endoscopic visualisation of the nerve using 1 or 2 incisions are popular in bilateral surgery with reduced time to work, however there are no benefits beyond 6 months and the added complications due to iatrogenous injury to the median nerve or one of its branches have a significant impact on patients and their recovery. I do not use endoscopic techniques in my specialist peripheral nerve practice. In diabetic patients with severe loss of function and proven peripheral neuropathy, careful consideration should be given to whether decompression should be performed as there is a risk of neuropathic pain as a result of re-perfusion of the ischaemic nerve and this can be debilitating. Adjuncts such as opposition tendon transfer reconstruction may be preferable in such cases to improve function.

    Setup

    Local anaesthetic infiltration to the skin of the distal forearm and the palm of the hand overlying the carpal tunnel is performed at least 10 minutes prior to the procedure. I use approximately 6mls of a 50:50 mix of 1% lignocaine and 0.5% chirocaine. This offers fast onset and useful duration of approximately 2-4hours for post-operative pain relief. I use aa forearm tourniquet for the nerve exposure and decompression, however substituting the lignocaine for a 1:200,000 solution of lignocaine and adrenaline and administering the injection at least 20 minutes prior to the procedure provides an alternative relatively bloodless field that means the procedure can be performed without a tourniquet. I use this alternative strategy when there is a contraindication to tourniquet use such a sin the case of an ipsilateral arteriovenous fistula for haemodialysis.
    The patient is semi reclined with the arm extended on a side table. The skin is prepared with suitable surgical site preparation and the limb draped above the elbow. The skin sensation is checked at this at this stage to ensure anaesthesia at the site of surgical incision. A sterile and disposable tourniquet is placed around the proximal forearm and the limb is elevated prior to elevation of the tourniquet at approximately 250mmHg.
    In a revision case or a case where pathology is expected (tumour, synovitis in rheumatoid arthritis) I would suggest using a regional anaesthetic block at the level of the plexus in the upper arm to provide sufficient anaesthesia for a longer operation and increase the duration of tourniquet tolerance to reflect the likely longer duration of surgery. In such cases I would use an Esmarch rubber bandage to exsanguinate the limb due to the vasodilatation that accompanies the regional anesthetic block. I would also use a lead hand to position and support the fingers to stabilise the hand and aid surgical exposure. I do not use this under local anaesthesia as patients find the extended position uncomfortable.

    Operation
    The case presented is performed under regional anaesthesia. Note the vasodilatation from the regional nerve block at the level of the infraclavicular brachial plexus. The nerve block causes a loss of sympathetic tone in the blood vessels of the hand. The right arm is positioned in the anatomical position on a side table.
    Mark the skin incision. The incision should be made along the radial side of the ring finger. This results in a scar that is ulnar to the median nerve and not immediately overlying it at the carpal tunnel. It also places the surgical incision between the median and ulnar nerve (within Guyon’s canal). The extended thumb provides a guidance for Kaplan’s line shown here dotted. This line marks the superficial palmar arch and is a useful guide during exposure of the distal part of the carpal tunnel decompression.
    The hand has been exsanguinated with an Esmarch bandage and positioned in a lead hand to stabilise the hand and fingers for the surgical approach. The lead hand maintains full supination and prevents the tendency to pronation that may result in inadvertent dissection ulnarwards with a risk of injury to the ulnar nerve, rather than the correct deep dissection perpendicular to the skin incision.
    The skin is incised in the line of the surface markings from Kaplan’s line to the volar wrist crease. Look for any large sensory cutaneous branches crossing the subcutaneous fat. Inadvertent transection of these branches may result in a painful scar.
    Spread the skin edges with tenotomy scissors and expose the longitudinal white fibres of the palmar aponeurosis. The hypothenar fat pad is seen in the proximal and ulnar part of the wound. This should be protected and cases of revision decompression surgery and neurolysis can be elevated as a vascularised turnover fat graft to cover the median nerve.
    Split the fibres of the palmar aponoeurosis and position a small self retaining retractor in the wound edges to expose the superficial transverse fibres of the flexor retinaculum.
    Use sharp dissection with a scalpel blade to cut through the ulnar side of the exposed flexor retinaculum in the line of the ring finger and perpendicular to the skin incision. The flexor retinaculum inserts distally and ulnarly to the hook of the hamate. This boney landmark can be easily palpated in the wound and acts as a guide for exposure of the flexor retinaculum which should be incised radial to the hook of the hamate. Avoid exposing the ulnar nerve in the distal end of the incision, especially in older patients where a tortuous and ectatic ulnar artery and poor connective tissues may displace the ulnar nerve in a radial direction. If the forearm is not fully supinated there is a tendency to deep dissect in a progressive ulnar direction which increases this risk.
    Complete the division of the central portion of the flexor retinaculum and adjust the self retaining retractor deeper in the wound. This will keep the residual proximal and distal extnet of the flexor retinaculum under tension. The cut area will have convergent edges. The flexor retinaculum adgers will become parallel when the decompression if completed. Use a Ragnall retractor to assist exposure of the flexor retinaculum. A – Flexor retinaculum B – Median nerve with vasa nervorum C – Flexor tendon within carpal tunnel
    Use tenotomy scissors in a spreading action above the flexor retinaculum to expose the distal compression points and identify the fat pad and the superficial palmar arch just beyond the flexor retinaculum.
    Use shap dissection with a scalpel to release the distal flexor retinaculum. The digital flexor tendons are visible in the carpal tunnel. The median nerve will be visible in the radial side of the carpal tunnel but is still covered by the radial edge f the flexor retinaculum. Once the two convergent edges of the retinaculum become parallel, the distal dissection is almost complete. Gently use the tips of the tenotomy scissors to expose the common digital nerve branches at the distal extent of the carpal tunnel and note the postion of the superficial palmar arch. Ensure there are no fibrotic bands crossing the nerves that may cause peristent compression during the post operative period when swelling predisposes to further nerve compression.
    Now use a Ragnall retractor to expose the proximal undivided flexor retinaculum. The proximal retinaculum must be fully released proximal to the wrist crease where it merges with the distal forearm fascia which is often thickened and contributes to nerve compression where the median nerve passes superficially from beneath the flexor digitorum superficialis to lie in the interval between palmaris longus and flexor carpi radialis.
    The proximal skin edge has been lifted with a skin hook to allow blunt dissection between the skin and the flexor retinaculum in preparation for the proximal release.
    The proximal flexor retinaculum is cut under direct vision and the interval is developed into the distal forearm to release the antebrachial fascia. Releasing the fingers from the lead hand and flexing the wrist aids exposure and allows the median nerve to drop away from the retinaculum and reduces the risk of inadvertent injury. It is preferable to expose the proximal fascia fully and divide it in one cut rather than piecemeal which requires repeated retraction and progressive difficulty in visualising the most proximal extent. The interval for proximal extension should be along the ulnar side of the palmaris longus. This avoids direct scar over the median nerve, reduces the risk of iatrogenous injury and also avoids the risk of leaving a palmar aponeurotic band arising from palmaris in continuity crossing the proximal nerve. If the proximal fascia cannot be visualised directly for decompression, have a low threshold for extending the incision proximally with a 1.5cm oblique ulnarwards incision from the wrist crease. The decompression is then easy to complete proximally. I use the proximal extension in approximately 1:20 of my primary carpal tunnel decompressions and in all revision operations.
    The release is now completed both distally and proximally. The self retaining retractor can be repositioned to allow exposure of the carpal tunnel contents. The median nerve is lying free in the radial side of the wound. Elevate the radial flexor retinaculum cut edge and ensure that the median nerve isn’t tethered to the undersurface of the retinaculum. A gentle external neurolysis to release any tether points may be undertaken at this stage. I look for the motor branch of the median nerve in all cases, mainly to ensure that the branch has no aberrant proximal transretinaculum course that may pose a risk of entrapment or a risk on injury in the rare case of revision carpal tunnel surgery being necessary at a later date. If there is significant motor involvement with thenar wasting then I always trace the motor branch to muscle ensuring that there are no entrapment points at the distal retinaculum. Note the condition of the nerve and any fixed deformity at the site of maximum compression and any pre-stenotic dilatation. Note any other abnormal nerve findings including persistent median artery, bifid median nerve atrophy. I do not undertake epineurotomy and internal neurolysis which has been suggested extremely scarred nerves. I do not think that it improves the outcome and I worry that it may create more scar tether points on the nerve and impair neural gliding. Examine the rest of the canal contents for synovial thickening, ganglia and tumours.
    If the procedure is under local anaesthesia I release the tourniquet at this stage and apply pressure over the wound for 2 minutes. After this I use bipolar diathermy for haemostasis of any major bleeding points. If under a regional block, a tourniquet flush and re elevation will identify any major bleeding points and allow haemostasis. Place interrupted nylon sutures in the wounds edges.
    The closure is completed with 4-5 interrupted nylon sutures. I prefer to avoid subcuticular closure as some patients have a scar thickening which can take a few months to resolve.
    The wound can then be covered with a non adherent dressing and padded with gauze.
    A bulky wool and crepe dressing is applied from the distal forearm to the distal palmar crease. The metacarpophalangeal joints should be able to full flex. The patient should have the limb elevated in a high sling for 24 hours post operatively to reduce swelling, pain and wound site tension.
    Post Operative

    Elevate the hand in a high sling for 24 hours
    Encourage functional use of the hand for light assist gripping tasks. This allows the wrist to extend and the flexors to glide preventing adherence to the site of surgery and also preventing volar subluxation of the tendons towards the scar.
    Reduce the bulky bandage at 5-7 days post operatively and inspect the wound and change the under dressing to a small dry occlusive dressing. Examine for any wound complications (haematoma, infection) at this stage.
    Encourage further functional use of the hand at this stage.
    Remove sutures between 10 and 14 days.
    Start moisturising cream gentle scar massage from 2-3 weeks and continue until 6 weeks. This encourages scar maturation and reduces scar sensitivity.
    Assess at 6 weeks for symptom resolution and check for scar sensitivity.

    Recommended Reading

    The results of carpal tunnel decompression are generally predictable and good. Jeremy Bland has documented poorer outcome in cases where there is mild neurophysiological carpal tunnel or severe, perhaps representing diagnostic confusion in the former and severe nerve impairment in the latter. Outcome is less predictable in patients with diabetes and with peripheral neuropathy. Peripheral neuropathy is not a contra-indication to surgery however careful consideration should be given to severe compression cases with little preserved function who remain pain free because occasionally neuropathic pain may develop following decompression. The effects of scar pain and tenderness can be minimised with careful surgical technique avoiding injury to the cutaneous branches in the palm, early functional use of the hand, scar massage and desensitisation. Severe motor dysfunction with loss of thenar bulk does not recover with decompression and adjunctive tendon transfers should be considered in such cases to improve hand and thumb dexterity for opposition grip.

    References:
    Levine DW, Simmons BP, Koris MJ, Hohl GG, Fossel AH, Katz JN. A self-administered questionnaire for the assessment of severity of symptoms and functional status in carpal tunnel syndrome. J Bone Joint Surg Am 1993;75:1585-1592
    Fowler JR. Nerve Conduction Studies for Carpal Tunnel Syndrome: Gold Standard or Unnecessary Evil? Orthopaedics 2017;40(3):141–142
    Kaile E, Bland JDP. Safety of corticosteroid injection for carpal tunnel syndrome. J Hand Surg Eur 2017 Jan 1:1753193417734426. doi: 10.1177/1753193417734426 [Epub ahead of print]
    Bland JD. Do nerve conduction studies predict the outcome of carpal tunnel decompression? Muscle Nerve 2001 Jul;24(7):935-40
    Bland JD. A neurophysiological grading scale for carpal tunnel syndrome. Muscle Nerve 2000 Aug;23(8):1280-3
    Tang CQY, Lai SWH, Tay SC. Long-term outcome of carpal tunnel release surgery in patients with severe carpal tunnel syndrome. Bone and Joint Journal 2017 Oct;99-B(10):1348-1353

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