Compression neuropathies of the radial nerve

The commonest cause of radial nerve dysfunction is from extrinsic compressions of the radial nerve, such as against the shaft of the humerus in “Saturday night palsy”. However, this chapter focuses on the less common intrinsic compression neuropathies of the radial nerve. Intrinsic radial nerve compression neuropathies occur much less frequently than those of the median or ulnar nerves. The combined annual incidence of compressive neuropathies of the posterior interosseous nerve and the superficial radial nerve is only 0.003%, compared to an annual incidence 0.1–0.35% for carpal tunnel syndrome and 0.03% for ulnar nerve compression syndromes. Three radial nerve compression syndromes are described: Radial Tunnel Syndrome (RTS); Posterior Interosseous Nerve (PIN) syndrome; and compression of the Superficial Radial Nerve (SRN) in Wartenberg’s syndrome [1]. Compression neuropathies of the radial nerve Radial nerve anatomy Knowledge of radial nerve anatomy is required in understanding and differentiating these three radial nerve compression syndromes. The posterior cord of the brachial plexus becomes the radial nerve once the axillary nerve branches off through the quadrangular space at the lower border of teres minor muscle. The radial nerve exits the axilla via the apex of the lateral muscular triangle to enter the posterior compartment of the arm. Lying deep to triceps, the radial nerve passes from superomedial to infero-lateral through the spiral groove on the posterior aspect of the humerus. At approximately the junction of the middle and distal third of the arm the radial nerve turns anteriorly, around the lateral border of the humerus, and pierces the lateral antebrachial septum to enter the anterior compartment of the arm 10 to 12 cm above the elbow. Here it enters the radial tunnel, a musculofascial space formed in its proximal part by biceps and brachialis muscle antero-medially, brachioradialis, extensor carpii radialis longus and extensor carpii radialis brevis muscle antero-laterally; the radio-capitellar joint capsule forms the floor. Within the radial tunnel the radial nerve divides into the Posterior Interosseous Nerve (PIN) and Sensory Branch of the Radial Nerve (SRN) 6.0 to 10.5 cm distal to the lateral intermuscular septum and 3 to 4 cm proximal to the aponeurotic leading edge of the superficial (humeral) head of the supinator muscle (the Arcade of Frohse). The SRN travels deep to brachioradialis muscle until around 8 cm proximal to the radial styloid, where it pierces the deep fascia at the lateral edge of brachioradialis muscle to run superficially and supply sensation to the radial distribution of the dorsum of the hand. The PIN passes in an oblique course between the two heads of supinator muscle to enter the posterior compartment of the forearm [2, 3]. The PIN supplies motor innervation to all the extensor muscles of the wrist and digits except for the extensor carpi radialis longus (ECRL) which is supplied by a branch typically from the radial nerve prior to its division into the PIN and SRN. The PIN divides into a medial (superficial) branch innervating extensor carpi ulnaris muscle (ECU), extensor digiti minimi muscle (EDM), and extensor digitorum communis muscle (EDC), and a lateral (deep) branch to abductor pollicis longus (AbPL), extensor pollicis brevis (EPB) and longus (EPL) and extensor indicis muscle (EI) [4]. The PIN is often described as a “motor-only” nerve, but it does also carry sensory afferent fibres from the wrist, as well as group A beta afferent nerve fibres from the muscles along its distribution [5]. Radial tunnelsyndrome (RTS) Introduction Michele and Krueger first described radial tunnel syndrome in 1956. They used the term radial pronator syndrome, as they identified axial rotation of the forearm in the aetiology of this condition [6]. Since then radial tunnel syndrome has remained one of the major controversies in upper limb surgery. Does it even really exist, what is its incidence and how do you clinically test for it?