Short Notes in Plastic Surgery

February 19, 2018

67. Compressive Neuropathy of the Ulnar Nerve

Filed under: Chapter 67,Uncategorized — ravinthatte @ 4:32 am

67. Compressive neuropathy of the ulnar nerve

The compiler of these short notes acknowledges the help of Drs. Mukund Thatte from Mumbai and Rajendra Nehete from Nashik in India both plastic surgeons with special interest in surgery of the hand in writing this chapter. The cadaveric dissections were performed by Professor Maksud Devale assisted by Sumit Hadgaonkar as well as Neeraj Bhaban both senior residents; all from the department of plastic surgery at the Lokmanya Tilak municipal medical college and hospital in Mumbai. Professor Natrajan the head of the department of anatomy of the above institutions was kind enough to allow the dissections.

  1. The ulnar nerve is a mixed nerve and is a terminal branch of the medial cord borrowing its fibres from the C8 and T1 nerve roots.

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  1. Like the median nerve it is vulnerable to compression as it traverses across the elbow and the wrist though the sites in the case of the ulnar nerve are different. Approximately 8 to10 centimetres above the medial epicondyle of the humerus the ulnar nerve lies posterio-medial to the brachial artery and anterior to the medial head of the triceps and is posterior to the medial inter-muscular septum. This septum is continuous from the medial epicondyle to the coraco-brachialis muscle. A fibrous arcade extending from the intermuscular septum and made of the deep brachial fascia covers the ulnar nerve at this site and may compress the nerve. This fibrous arch was described by John Struthers the Scottish anatomist and is named after him. The previous chapter on compression of the median nerve around the elbow also included a similar ligament arising from an abnormal origin of the pronator teres from the humerus which too was described by John Struthers and is named after him.

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Dissection specimens courtesy Maksud Devale, Sumit Hadgaonkar and Neeraj Babhan.

  1. From here on the ulnar nerve lies behind the medial epicondyle and is medial to the olecranon. This is the cubital tunnel the roof of which is formed by a tough and somewhat taut fascial layer which extends from the origin of the flexor carpi ulnaris on the humerus named after Osbourne. Barring this fascial structure the nerve for all practical purposes is subcutaneous at this point. From here the ulnar nerve enters the forearm between the humeral and ulnar head of the flexor carpi ulnaris.

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  1. All the structures mentioned above may be associated with a compression of the nerve the commonest probably being in the cubital tunnel and this is the second most common compressive neuropathy after the carpal tunnel syndrome involving the median nerve in the arm described in the previous chapter.
  2. While taking the history of the patient suspected of having compression of the nerve around the elbow, past injuries around the elbow joint should be enquired into. This includes injuries or fractures around the elbow. Any occupation involving movements which would lead to a valgus stress should also be enquired into and noted. Rarely a single episode of a severe twisting injury or a hyper extension injury can lead to an ischemic episode leading to neuritis and which might resemble later as a cubital tunnel syndrome. The symptoms usually begin with tingling and numbness in the little and ring fingers accompanied by pain and tenderness in the medial half of the elbow particularly over and around the medial epicondyle and is severe when the nerve is pressed upon in the humeral sulcus or the cubital tunnel. As the condition progresses the weakness of the ulnar intrinsic muscles can lead to clumsiness in actions involving adduction of the thumb and disturbance of proprioceptive actions. Overtime the wasting of the muscles on the ulnar side of the palm becomes quite evident. A Tinels sign is almost always positive from the beginning. Active flexion of the elbow against resistance causes pain at the site and a combination of local pressure and the flexion manoeuvre up to sixty seconds leading to severe pain is conclusive of the diagnosis in a vast majority of cases. In early stages conservative treatment with splints anti- inflammatory agents and a temporary change in the job description may help the condition. Soft padding around the elbow to prevent trauma or counselling on how to prevent certain actions can also give relief
  3. As with the compressive neuropathy of the median nerve at and around the elbow a differential diagnosis of the exact cause of the compression of the ulnar nerve around the elbow may not be always possible because the nerve though compressed in the cubital tunnel might also have other contributing factors for example a pincer action of the two heads of the origin of the flexor carpi ulnaris muscle or a fascial band above the elbow called the Struthers ligament. (Please see para2) All the hard and soft parts in this area develop from modification of the same mesenchymal mass and the condition might be a single phenotype with adjoining abnormalities. This probably has a bearing on the surgical procedure that is employed where a complete exposure of the nerve above and below the elbow is safer from the point of view of giving a final and a lasting result. Generally speaking the results of surgery to decompress the ulnar nerve around the elbow are not as satisfactory as after the release of the carpal tunnel syndrome and for this reason nerve conduction studies play an important role in locating the compressive lesion more accurately or to rule it out and arrive at a diagnosis of a non-obstructive neuropathy
  4. Compression of the nerve and the consequent symptoms and signs which result from reduction of the space in the cubital tunnel following injuries such as fractures are outside the description given in the preceding paragraph and form a distinct entity. A sequestrum, osteophytes or a shallow sulcus following a malunion forcing the nerve to displace\sub-luxate outside the tunnel during flexion among other things can play a part in the ensuing pathology also called a tardy palsy. In such cases an anterior transposition of the nerve after adequate decompression of all offending structures around the cubital tunnel is considered the best possible treatment. The question as to if a sub muscular placement is better than a subcutaneous\sub fascial placement when the nerve is transposed is a matter of debate though the subcutaneous\sub fascial placement is by-far the simpler of the two options. As explained in the previous paragraph the procedure of anterior transposition must ensure a fair amount of mobilisation of the nerve so as to eliminate any possible compression by causes enumerated earlier such as fibrous bands (ligament of Struthers) above the elbow and the pincer action of the dual origin of the flexor carpi ulnaris at the elbow. A medial epicondylectomy can be performed at the time of the anterior transposition if found necessary. Generally speaking an in-situ decompression with a limited incision is not favoured because should it fail subsequent surgery to transpose the nerve becomes that much more difficult. Localised lesions above and at or below the elbow with a normal capacious cubital tunnel are uncommon and have to be proved by conduction studies as mentioned earlier.
  5. The incision for the procedure is vertical and is centred on a point between the medial epicondyle and the olecranon and extends about eight cm. superiorly. It is most convenient to expose the ulnar nerve first in the ulnar sulcus behind the medial epicondyle and then trace it upwards and in so doing identify a cutaneous branch of the antebrachial nerve and retract it out of harm’s way. The medial intermuscular septum is next identified which lies anterior to the nerve and any fascial structures going across the nerve from the septum are released including any offending fibres of the septum itself. This is the area purportedly of the Struthers ligament. The nerve is then followed downwards into the cubital tunnel and its passage through the pronator\flexor origin is inspected for any compressive pathology and if present this is released. At this point the nerve is inspected for any subluxation out of the cubital tunnel while flexing and extending the elbow. The tunnel itself is inspected for any post traumatic artefacts or an abnormally large medial epicondyle. The artefacts are cleared and a medial epicondylectomy can be performed at this stage if indicated. If the cubital tunnel is shallow and if this shallowness is responsible for the subluxation of the nerve  a decision is taken to transpose the nerve anteriorly.  In so doing the connective tissue around the nerve is kept intact so as to preserve its blood supply most of which runs along the nerve and this is best done by retracting the nerve by a soft catheter around it. As the ulnar nerve gets gently retracted, its branches from its posterior surface to the flexor carpi ulnaris and the ulnar profundus muscles come into view. They need to be preserved if necessary by gentle teasing and mobilisation. A thorough distal inspection of the nerve is then performed and any fibrous bands likely to impinge on the nerve in its new transposed position are cut away. In order that the nerve does not regress to its earlier position the soft tissue under the skin flap is sutured to a part of the anterior periosteum of the medial condyle to prevent the nerve sliding back irrespective of the  new placement of the nerve sub fascial or sub muscular. The skin is closed in one layer which includes the subcutaneous tissue. Because the incision extends into the lower half of the upper arm the tourniquet is applied a little higher and most surgeons prefer general anaesthesia for the procedure.
  6. Below are reproduced photographs of a patient who had both, the ulnar and the medial nerve pathology following a supra-chondylar fracture, corrected and fixed with implants. Pictures provided by Rajendra Nehete, plastic and hand surgeon, Nasik, Maharashtra, India.

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The following pictures are of Ulnar nerve transposition courtesy Mukund Thatte, plastic and hand surgeon, Mumbai involving an abnormal insertion of the triceps, compression by the Struthers ligament  as well as compression in the cubital tunnel.

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  1. From here on the ulnar nerve courses over the interosseous membrane till it approaches the wrist where it lies superficial to the flexor retinaculum and then divides into two branches superficial and the deep The superficial branch supplies the palmaris brevis a cutaneous muscle and supplies sensations to the whole of the little finger and the ulnar side of the ring finger as well as the hypo-thenar area. The deep branch of the ulnar nerve is more important because it supplies all the interosseous muscles (both palmar and dorsal) the adductor of the thumb and the ulnar lumbricals. A structure called the piso-hamate ligament crosses superficial to the passage of the ulnar nerve over the flexor retinaculum and encloses it in a tunnel named after Guyon who described it in 1861. The ulnar nerve is vulnerable to compression in this area by sheer lack of space (sometimes brought on by inflammation in the surrounding area and may be temporary) or by space occupying lesions such as a ganglion, post traumatic residue of a fracture of the hook of the hamate or its non-union, non-specific inflammatory conditions or a post traumatic aneurism of a branch of the ulnar artery which lies medial to the nerve on a deeper plane and is separated from the nerve by a fascial structure. Repeated trauma to the hypothenar area adjoining the wrist or sustained pressure to the area by a handle of a two-wheeler is known to cause a compressive neuropathy in this area. This condition is far less common than the carpal tunnel syndrome but it can lead to clumsiness of actions involving the adductor muscle wasting of the hypothenar area and may result in clawing of the ulnar fingers with extension at the M.P. joints and flexion of the interphalangeal joints  As in other compressive neuropathies the condition begins with altered sensations (in the hypothenar area in this instance) tingling and numbness and a deep ache. The differentiating feature being intact sensation on the dorsum, since the dorsal sensory branch is given proximal to the wrist in the lower part of the forearm and is not compressed.

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  1. In mild early cases a splint in a neutral position and rest and reducing pressure on the hypothenar area might help the patient. In more severe cases where pain is exacerbated by local pressure or by forced radial deviation and muscles are affected surgery will need to be undertaken after an x ray preferably a C.T scan to look for undiagnosed fractures of the hamate particularly in the region of its hook. A M.R.I. can also help to diagnose soft tissue lesions that might be causing pressure on the Guyon’s canal. An electro diagnostic test such as a sensory nerve action potential (SNAP) of the ulnar nerve will help confirm compression. Such diagnostic precautions are essential because the condition is uncommon its muscular manifestations are not always apparent and a post traumatic arthritic pathology in the region might be all that the patient has and can be treated without surgery.
  2. The incision in the palm used to release the median nerve from the carpal tunnel can also be used to release the ulnar nerve from the Guyon’s canal except that it might have to be extended by about a centimetre proximally towards the wrist and also across it parallel to its transverse crease (please see diagram above). The soft tissues are incised and retracted and the free border of the hypothenar muscles is identified. The hook of the hamate is palpated by the tip of the index finger and the Guyon’s canal is located. It is in the region of the fascia covering the proximal free border of the hypothenar muscles that the deep branch of the ulnar nerve makes its appearance after going around the hook of the hamate and travels across the palm to supply the adductor of the thumb and is usually accompanied by a leash of blood vessels. The fascia in the proximal part of the hypothenar muscles needs to be carefully tenotomised to expose the deep branch fully and is then traced proximally to its origin from the ulnar nerve which is then released from the confines of the Guyon’s canal by de-roofing it with a scissors introduced in the canal. A carefully introduced small right angled retractor when lifted will demonstrate if the canal is fully opened or not and will also determine the presence of any tightness of the ante brachial fascia. The release of this fascia if required as well as the release of the canal is helped greatly by the transverse extension of the vertical incision. All operative steps are undertaken under vision with magnification and the fact that the ulnar artery lies medial and deeper to the nerve must be borne in mind. Also if the cause of the compression happens to be a small post traumatic loose piece of the Hamate bone (sequestrum) or an abnormal post traumatic dilatation of a blood vessel (an aneurism) those conditions must be dealt with. The wound is closed after haemostasis. The nature of anaesthesia for this procedure is no different from the ones used for the release of the carpal tunnel syndrome which have been narrated in the previous chapter. Following photographs have been supplied courtesy Rajendra Nehete, hand and plastic surgeon, Nashik, Maharashtra, India. The incision employed here is similar to the one described in the text above.

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The following pictures are kindly provided by Mukund Thatte, hand and plastic surgeon, Mumbai.

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