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Median and ulnar nerve decompressions

    Overview

    Learn the Median and ulnar nerve decompressions surgical technique with step by step instructions on OrthOracle. Our e-learning platform contains high resolution images and a certified CME of the Median and ulnar nerve decompressions surgical procedure.
    Compression of the ulnar nerve within Guyon’s canal is uncommon and is often seen in association with a local space occupying lesion such as an aneurysm or a piso-triquetral ganglion.
    Median nerve compression within the carpal tunnel however, represents the commonest peripheral nerve entrapment treated by hand surgeons.
    Decompression of each nerve individually is dealt with in the relevant sections on Orthoracle.com
    In the rare situation that both median and ulnar nerves are compressed at the wrist, decompression and complete visualisation of both nerves may be achieved through a single ulnar sided approach which is described here.
    All of the typical causes of median or ulnar nerve entrapment described elsewhere may contribute to a combined compression.
    In the setting of a peripheral nerve clinic, combined compression of both median and ulnar nerves at the wrist is often seen in the context of a more proximal, cord or trunk level brachial plexus injury. Observing such patients recovery over several months may reveal a sudden slowing or even arrest of regeneration as the regenerating front approaches a fibro-osseous canal or tunnel. Although still poorly understood, some authors suggest that this phenomenon relates to an auto-compression of the nerve as it’s volume increases during axonal regeneration.
    The key factors for a successful outcome in combined median and ulnar nerve decompression through a Guyons canal approach are firstly, adequate decompression and visualisation of the deep motor branch of the ulnar nerve by careful division of the hypothenar tendinous arch at the hook of hamate, and secondly, decompression of the median nerve by release of the transverse carpal ligament from its ulnar sided attachments.
    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
    Carpal tunnel decompression
    Median nerve neurolysis, resection and reconstruction using Axogen AVANCE processed nerve allograft

    Indications

    INDICATIONS
    Current indications for carpal tunnel decompression are the presence of symptoms for three months or more and failure of non-operative measures such as night splints or steroid injections to provide adequate symptom relief. The presence of sensory or motor axonal loss is an indication for more urgent surgical intervention.
    Decompression of the ulnar nerve within Guyon’s canal is performed for local compression due to a local tumour, ganglion, or local trauma to the nerve. It is is an uncommon site of nerve compression. Other less common causes include an pseudoaneurysm, or aneurysm related to hypothenar hammer syndrome. Chronic compression in cyclisting enthusiasts is occasionally seen, as is a non-union of the hook of hamate.
    Combined median and ulnar nerve compression at both Guyon’s canal and the carpal tunnel are uncommon. In my peripheral nerve practice, combined compression of both median and ulnar nerves at the wrist often occurs in the context of a more proximal, cord or trunk level brachial plexus injury. Observing such patients recovery over several months may reveal a sudden slowing or even arrest of regeneration as the regenerating front approaches a fibro-osseous canal or tunnel. Although still poorly understood, some authors suggest that this phenomenon relates to an auto-compression of the nerve as it’s volume increases during axonal regeneration.
    If simultaneous decompression of both nerves is indication a single approach as detailed here provides complete decompression and direct visualisation.
    SYMPTOMS & EXAMINATION
    Patients may complain of both ulnar and median sensory symptoms with pain, parasthesia and numbness over all finger tips. Sparing of both the territory supplied by the palmar cutaneous branch of the median nerve (the skin over the thenar eminence) and the dorsal sensory branch of the ulnar nerve (the skin over the dorsum of the 4th and 5th metacarpals) precludes a more proximal compression. Localisation may be further confimed if either compression is severe enough to have lead to motor weakness or muscle wasting. Typically the ulnar sided FDPs would be spared in a Guyons canal entrapment of the ulnar nerve. The ulnar innervated intrisics may be weak and wasted and Froments sign may be positive. (A paper test that demonstrates use of flexor pollicis longus to compensate for a weak adductor pollicis). Similarly, severe median nerve compression at the carpal tunnel may cause thenar muscle wasting. A Tinel-Hoffman sign is useful to locate the site of compression and to rule out more proximal sites of compression. An assessment of radial and ulnar pulses at the wrist and an Allens test is important to assess ulnar artery function and to establish the dominant blood supply to the hand.
    INVESTIGATIONS
    Plain radiographs may demonstrate joint degeneration at the piso-triquetral joint or a non-union of the hamate.
    An ultrasound or MRI scan may be useful where compression in Guyons canal is suspected and may demonstrate a space occupying lesion. This is an important part of the investigation.
    Median nerve compression at the carpal tunnel does not typically require imaging as a prelude to surgery.
    Neurophysiology will demonstrate slowing of conduction velocities across the carpal tunnel and Guyon’s canal. In more significant or prolonged compression ectromyography may demonstrate an element of denervation within the intrinsic muscles. Abductor pollicis brevis (APB) is typically tested in carpal tunnel syndrome and the adductor pollicis or first dorsal interosseous (FDI) for the ulnar nerve. Testing may demonstrate denervation manifested by the presence of positive sharp waves and fibrillations.
    ALTERNATIVE OPERATIVE TREATMENT
    In severe compression syndromes with longstanding muscle wasting and functional loss, decompression may fail to restore motor function. Consideration must therefore be given to tendon transfers for thumb opposition and anticlaw procedures. These may be performed at the time of nerve transfer if motor recovery is expected to be incomplete.
    NON-OPERATIVE MANAGEMENT
    Once sensory or motor loss have become established, surgical decompression is mandated and non-operative measures may delay definitive treatment and compromise the final outcome. Early Guyon’s canal entrapment may be successfully treated with splinting. The various non-operative measures for carpal tunnel syndrome and their exact role are detailed in the relevant section.
    CONTRAINDICATIONS
    Surgical decompression is contraindicated if the patients general fitness precludes surgery. Surgery should be delayed if there is local infection.

    Setup

    Under either general or regional anaesthesia, the patient is positioned supine with the arm on an arm table.
    An upper arm tourniquet is applied.
    The hand is placed into a lead hand.
    Loupe magnification is essential.
    Bipolar diathermy is set up with fine tipped forceps.
    A Mixter and some sloops may be useful.
    The limb is prepared up to the elbow and draped.

    Operation

    Mark the skin incision over Guyons canal with a curvilinear line
    This crosses the midway point between the pisiform and hook of hamate. It extends 0.5cm distal to the hook of hamate.
    A – wrist crease
    B – Hook of hamate
    C – Pisiform

    Incise the skin with a bladeThe skin is incised.
    Skin hooks are held by the surgeon and assistant.

    Enter the superficial tissues overlying Guyons canalThe fat overlying Guyons canal is entered.
    Palmaris brevis is sometimes encountered at this level and should be divided.
    The volar carpal ligament constitutes the roof of the canal and will be encountered deep to this fatty layer

    A small self retainer is placed in the wound and superficial volar carpal ligament is carefully divided.
    In the distal half of the incision there is often a cutaneous branch of the ulnar nerve supplying the hypothenar skin. This should be protected once identified.

    More proximally the thick transverse fibres of the volar carpal ligament that make up the roof of Guyon’s canal are divided. These are continuous with the antebrachial fascia proximally.
    This thicker layer extending into the forearm may be responsible for residual compression proximal to Guyons canal if not formally released.

    Once the volar carpal ligament is divided, the ulnar artery and nerve are now exposed within Guyons canal and can be mobilised.
    The nerve at this superficial level contains two major components. It is important to note that both are sensory branches, one to the small finger ulnar digital and the other to the fourth web respectively. The deep motor component has not yet been exposed.

    In order to expose the deep motor branch of the ulnar nerve, the ulnar artery requires further mobilisation.There is a consistent ulnar sided branch (labelled A) in the mid point of the incision that requires ligation or coagulation.

    The side branch is carefully mobilised and coagulated with a bipolar diathermy.
    The diathermy must be set to a low enough setting to avoid inadvertent injury to sensory nerve branches that lie in close proximity.

    The artery lies lateral to the nerve in Guyons canal and is mobilised medially to expose the hook of the hamate.This may be palpated at this stage to confirm its position. Its current position is under the distal part of the artery in this image.

    The artery and sensory branches are retracted medially.
    The hook of hamate is palpated laterally and is marked with a dot.

    Identify the hypothenar insertion onto the hook of hamate and its tendinous archThe hook of the hamate is a prominent bony landmark that is clearly palpable. For ease of visualisation I have marked its position with a blue dot.
    The deep motor branch runs under the hypothenar arcus tendineous in close proximity to the base of the hook of hamate.
    This is the free edge of fibrous tissue that is seen at the most proximal edge of the hypothenar muscles at the level of their insertion into the hook of hamate.

    Divide the ligamentous arch overlying the deep motor branch of the ulna nerve.Sharply dividing the ligamantous tissue just medial to the hook of hamate will expose the nerve. The flexor digiti minimi brevis inserts into this ligamentous arch.
    Great care is taken to avoid inadvertent injury to the nerve as it cannot be seen until the arch is divided.

    Expose the deep motor branch of the ulnar nerve which is now visible through the split in the fibres of the arch just medial to the hook of hamate.As it is entered, one often encounters the bone of the hook of hamate and must carefully move in a slightly ulnar direction towards the ligament and away from the bone itself.

    Divide the tendinous arch fully under direct visionThis opening in the tendinous arch is extended proximally and distally taking great care to protect the deep motor branch lying just underneath it.
    Proximally there is a free edge at this level.

    Confirm adequate decompression in Guyons canal by tracing the nerve proximally and distally.The motor branch is seen running around the hook of hamate, under the ligament, with the artery and ulnar sensory branches lying superficially.
    A – motor branch

    The ulnar nerve within Guyon’s canal has now been fully decompressed with the artery and superficial sensory and deep motor components all visualised.

    Mark out the transverse carpal ligament fibres as they insert into the hook of hamate and pisiformAttention is now turned to the median nerve in the carpal tunnel.
    This is ordinarily entered though a separate incision.
    However the ulnar sided fibres of the transverse carpal tunnel insert into the hook of hamate and pisiform.
    Therefore they may be identified and divided through this approach.
    The hook of the hamate has already been marked and palpated in a previous step. The carpal tunnel lies just radial to this mark.
    The dotted line marks out the fibres of the transverse carpal ligament that will be divided under direct vision. This is the same release that is performed in a more conventional carpal tunnel decompression, only at a more medial location.

    Divide the ulnar sided fibres of the transverse carpal ligament to expose the median nerve.The transverse carpal ligament is divided sharply.
    The median nerve is seen lying within the carpal tunnel.

    The carpal tunnel is progressively opened through this approach.
    Care is taken to protect and avoid the ulnar sided neurovascular structures.

    Ensure an adequate distal release is performed, which must include the point at which the tendinous edge of the thenar and hypothenar muscles meet.Expose the median nerve in the carpal tunnel.
    The hypothenar muscles can be seen inserting into the hook of hamate
    The median nerve is seen lying within the carpal tunnel.

    The proximal decompression of the median nerve is continued into the forearm fascia under direct vision by dividing the deep fascial continuation.
    The median nerve is protected as the structures overlying its ulnar aspect are divided

    Confirm an adequate decompression of the median nerve.A complete proximal and distal decompression is confirmed.

    Perform a layered wound closure and then apply dressings.The wound is irrigated with normal saline, haemostasis achieved and the wound closed in layers. The tourniquet may be released at this point, particularly if there are concerns about bleeding.
    4/0 monocryl is used to place some interrupted deep dermal sutures followed by a 4/0 monocryl subcuticular suture.
    The wound is dressed with steristrips and a non-adherent dressing.

    Wool and crepe are wrapped.
    The arm is placed into a Bradford sling.
    The patient may be discharged home the same day if safe to do so.

    Post Operative

    The patient is sent home with oral analgesia such as cocodamol.
    The patient is instructed to elevate the limb.
    A 1 week post operative appointment is made to check the wound and commence some hand therapy that includes nerve gliding excerises.
    The sutures are absorbable and do not require formal removal.
    The patient is reviewed at six weeks in the outpatient clinic.

    Recommended Reading

    There are no recent reported results of combined median and ulnar nerve decompressions at the wrist using the approach described.
    Maroukis BL1, Ogawa T1, Rehim SA1, Chung KC2.
    Guyon canal: the evolution of clinical anatomy.
    J Hand Surg Am. 2015 Mar;40(3):560-5. doi: 10.1016/j.jhsa.2014.09.026. Epub 2014 Oct 29.
    A historically relevant overview of the anatomy at Guyons canal
    Kaiser R, Houstava L, Brzezny R, Haninec P.
    The results of ulnar nerve decompression in Guyon’s canal syndrome. Acta Chir Orthop Traumatol Cech. 2012;79:243-8
    About a third of cases in these series were associated with a ganglion. The vast majority improved significantly following decmpression.
    Mondelli M1, Ginanneschi F, Rossi A.Neurosurgery.
    Evidence of improvement in distal conduction of ulnar nerve sensory fibers after carpal tunnel release.2009 Oct;65(4):696-700.
    Division of the transverse carpal ligament during a typical carpal tunnel release may decompress the ulnar sensory fibres as this neurophysiological study demonstrates.

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