Short Notes in Plastic Surgery

April 3, 2018

68. Compressive Neuropathy of the Radial nerve

Filed under: Chapter 68,Uncategorized — ravinthatte @ 10:26 am

68. Compressive Neuropathy of the Radial nerve

The compiler of these short notes thanks Dr. Anil Bhat, Professor and Head, Department of Orthopaedics, Kasturba Medical College and Manipal Academy of Higher Education, for scrutinising the manuscript, general guidance and some illustrations. He has done notable work on compressive neuropathies in the arm. The cadaveric dissections were performed by Dr. Saumil Shah and Dr. Chirag Bhansali both senior residents in the department of plastic surgery at the Lokmanya Tilak municipal hospital and college Mumbai under the supervision of Dr. Maksud Devle a professor in the same department. Dr. Natarajan the head of the department of anatomy kindly allowed these dissections.

1.   The radial nerve receives contributions from the posterior cord of the brachial plexus from which it arises but also from all three trunks superior middle and inferior of the brachial plexus and therefore its root value is C5 6 7 8 as well as T1. It gives branches to all three heads of the triceps muscle as it emerges from the lower triangular space (Fig. 1).

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The nerve is accompanied at its exit from this space by the brachial artery. It then passes behind the humerus along its spiral groove and can be damaged at this site by fractures in the middle third of the humerus (Fig. 2 and 3).

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2.   In some of these cases of fractures of the humerus, the nerve can also be damaged during surgery when the fractures of the humerus are reduced and fixed by appliances. Rarely the radial nerve may be affected by a tardy palsy when the fracture comes to unite even though the nerve is in continuity. The spiral groove is also the area where the nerve can get compressed by a sharp edge on which the arm rests when the arm is extended and abducted during deep sleep or in a state of inebriation. In popular parlance, this is called the Saturday night palsy where all extensors of the wrist and fingers are paralysed. The condition usually recovers spontaneously though in the interim the hand needs to be splinted, at least at the wrist (in extension) to allow actions by the flexors.

3.   From here on the nerve pierces the lateral intermuscular septum to enter the anterior compartment and lies in a furrowed space between the brachialis on the medial side and the brachioradialis and then the extensor carpi radialis on the lateral side. It is in front of the lateral condyle of the humerus that it divides into the superficial and the deep branch also called the posterior interosseous nerve (PIN) and it is these two nerves that may suffer a compressive neuropathy which is the subject of this chapter. The superficial branch is sensory and is called radial sensory nerve (RSN). The PIN is purely motor. Please see figures 2 and 3 above.

4.   The RSN travels along the radial border of the forearm below the brachioradialis. Half way down in the middle of the forearm it becomes subcutaneous between the brachioradialis and the extensor carpi radialis brevis by piercing the deep fascia and it is at this site that pain along the nerve can be elicited by tapping to produce exaggeration of symptoms of its compressive neuropathy (Fig. 4 and 5 below). It divides into two main branches 5 centimetres proximal to the radial styloid one of which supplies the dorsal and the radial surface of the thumb and the other called the major dorsal branch supplies the dorso-ulnar surface of the thumb as well as the dorsal radial aspect of the index finger. Another branch supplies sensations to the dorso-radial surface of the index and the dorso ulnar surface of the long finger.

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Actions involving strong pronation and simultaneous ulnar deviation puts this nerve on maximum stretch and any profession involving such repeated action predisposes to a neuropathy of the nerve. Repeated use of a heavy screw driver is an example. It is worth noting that this action results in approximation of the brachioradialis and the extensor carpi radialis brevis which might compress the nerve as it emerges from under the deep fascia leading to repeated ischemia. In modern times a variety of wrist and forearm bands are used in many a sport as also in activities such as lifting weights in the gymnasia. This together with tight wrist watch belts or heavy bangles that Indian women wear and may cause friction and contribute to the compression.

The condition produces pain or paraesthesia along the nerve and its sensory distribution and can rarely lead to loss of sensations. The pain is exacerbated when the nerve is tapped as well as when the forearm is pronated and flexed ulnar wards at the wrist.

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Fritz de Quervains

One branch of this nerve is in close approximation to the first extensor compartment of the wrist (Fig. 4) which is known to undergo an inflammatory pathological constriction leading to pain and poor gliding of the long extensor and abductor of the thumb. The condition is named after Fritz de Quervains (1868-1940) who was mainly known for his study of thyroid disease but also described an inflammatory condition of the tendons in the first extensor compartment.

A neuropathy of the radial sensory nerve might coexist with de Quervains disease because the obstructed first compartment and the consequent inflammation may temporarily affect the nerve. The diagnosis is made by tapping over the first extensor compartment when pain usually does not spread along the distribution of the nerve if the condition is restricted to the first extensor compartment. An improper release of the first compartment without identifying and securing the nerve can however lead to consequences such as a painful neuritis or anaesthesia in the distribution of the nerve.

The entrapment of the radial sensory nerve can be treated surgically by an incision not more than 3 centimetres in length placed vertically over the course of the nerve at about the junction of the upper two thirds and the lower one third of the flexor aspect of the forearm (Fig. 6).

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In view of the small size of the nerve some form of magnification is advised. The first step is to identify the musculotendinous junction of the brachioradialis muscle. Then by retracting the skin posterio-laterally the extensor carpi radialis brevis tendon can be visualised. The wound is undermined proximally and then distally and the fascia between the two muscles is identified by inserting a small right-angled retractor on either side. The nerve may be seen emerging in the lower end of the incision. If not the fascia between the two muscles is incised and the two muscles are retracted in their proximal part and in the bed created by this retraction the nerve can be visualised. The incision in the fascia is then extended distally and then proximally for about 10 centimetres and this will suffice to completely decompress the nerve. Occasionally a part of the brachio radialis muscle might have to be resected along its vertical direction. Only the skin and subcutaneous tissue are closed leaving the deep fascia open. A supporting dressing across the wrist joint with a thin plaster slab is employed to give post-operative rest to the part.

5.   The posterior interosseous nerve (P.I.N) is the larger of the two branches of the radial neve and arises in front of the lateral epicondyle of the humerus but unlike the sensory branch enters the posterior compartment of the forearm between the two heads of the supinator (humeral and ulnar) muscle (Fig. 12 and 13 see below). But prior to that it may encounter a fibro-tendinous arcade originating from the radio humeral joint which merges with fascia covering the supinator muscle (Fig. 7 and 8). This structure is named after Fritz Frohse (1871-1916, German anatomist).

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6.   After emerging from the supinator muscle the nerve divides into a superficial and a deep branch. The superficial branch supplies the extensor carpi ulnaris the extensor digiti communis and the extensor digiti quinti muscles. The deep branch supplies both the long and short extensor of the thumb and its long abductor as well as the additional extensor to the index finger (indexus proprius). Prior to crossing the elbow the radial nerve supplies the brachialis the anconeus and the brachioradialis. The P.I.N. passes through a tunnel like structure near the elbow. The tunnel’s floor is formed by the capsule of the radio-ulnar joint. The tunnel’s medial wall is formed mainly by the tendon of the biceps muscle and also the brachialis. It’s lateral wall is formed by the brachio-radialis and the long and short extensors of the wrist. Of these the brachioradialis crosses across the tunnel over the nerve from the lateral to the anterior side partly forming the tunnel’s roof. The arcade of Frohse mentioned earlier in the preceding paragraph is also adjacent to this tunnel but its location might vary. The nerve can get compressed in this tunnel because of fibrous bands in between the two heads of the supinator muscle. Gray’s anatomy states that the nerve can also get compressed here by the sharp edge of the extensor carpi radialis brevis, ECRB (Fig. 9) or a leash of vessels from the radial recurrent artery which supply the brachioradialis muscle as well as the extensor carpi radialis longus muscle ECRL (Fig. 10).

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The leash of vessels is probably named after Henri A.K. Henry also wrote the well known book the Extensile exposures of the extremities (Fig. 11).

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7.   The main symptom of the radial tunnel syndrome is pain and paralytic effects of the muscles that the P.I.N supplies are rare except when the compression is severe or in post-traumatic cases where the nerve might be damaged within the radial tunnel. In non-traumatic cases the pain is classically produced by pressure over an area between the brachioradialis and the extensor carpi radialis longus. Pain is also caused when pressure is applied over the supinator when the forearm is being supinated. To rule out any pressure on the undivided radial nerve pressure is applied above the elbow between the tendon of the biceps and the origin of the brachioradialis just above the elbow when pain will not be felt. The diagnosis of the radial tunnel syndrome is mainly clinical and electrodiagnostic methods are not useful. Infiltration with local anaesthetic agents sequentially can help locate the area of entrapment.

Surgery to treat the radial tunnel / P.I.N.syndrome is performed by an incision along the posterior border of the brachioradialis muscle marked by asking the patient to flex the elbow in the mid prone position against resistance. The incision about 10 centimetres will expose the extensor carpi radialis longus (E.C.R.L.) on the lateral side and the brachioradialis on the medial side.

A very thin nerve the posterior cutaneous nerve of the fore arm can be identified here and should be saved. The area between the two muscles is occupied by a fascia which is incised sharply by retracting the two muscles. Further retraction will reveal vessels straddling the two muscles which are cauterized. A plane is developed between the two muscles above and below by blunt dissection with a finger. In the area thus created can then be seen both the superficial and deep (P.I.N.) branches of the radial nerve. The P.I.N. here can be seen entering the supinator muscle. The humeral superficial head of the supinator is then stripped off or incised over the humerus to release it and take away the compression of the P.I.N. The detached head of the muscle is then held and any fibrous bands between it and its deep origin are then cut away. At this stage a finger can be introduced in the proximal part of the incision at the level of the elbow and burrowed higher to take away any constricting elements around the main trunk of the radial nerve. Some surgeons as a form of caution detach the origin of the long radial extensor of the wrist (E.C.R.L.) from the lateral epicondyle just in case the condition was only one of lateral epicondylitis (Fig. 14-18 below).

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All above photographs courtesy Dr. Anil Bhat.

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