Radial/PI neuropathy

Proximal RN may be compressive or traumatic. It can be due to fracture of the humeral shaft and strenuous activity such as weightlifting. It can be due to crush or twisting injury of the wrist or forearm or repetitive pronation and supination at work. Intoxicated individuals sleep with their arm over a bench "Saturday night palsy" with injury to the spiral groove with or without fracture of the humerus. In newborns, the umbilicus can entrap the nerve. These lesions are triceps sparing. Nerve injury at axilla from improper crutches use affects the triceps and the triceps reflex. Fractures of the head of the radius affect the nerve more distally. Compression of the epicondylar branch is one of the types of tennis elbow. Pain and tenderness in the lateral elbow occurs, resembling lateral epicondylitis (another entity known as tennis elbow).

The clinical presentation of proximal RN is wristdrop, inability to extend the fingers, weakness of the brachioradialis and variable sensory loss in the first dorsal web space. If proximal enough it may affect triceps and posterior arm sensation. Athletes should have x rays to exclude fracture. Treatment is conservative including a wrist splint, with surgery reserved for cases that have not improved by four months. SUPERFICIAL RN in forearm can be caused by repetitive pronation/supination maneuvers. The presentation is paresthesias over forearm, wrist, thumb, and dorsal hand, maximal in with wrist flexed in ulnar deviation. Reduced SNAP over the dorsum of hand is seen. Local injection can be used to confirm diagnosis. Treatment is rest, and if unsuccessful, then surgical exploration. Tight watchbands and handcuffs can also cause this (the latter with or without median and ulnar sensory effect). In the forearm, the radial nerve divides into a superficial sensory branch and a deep motor branch (posterior interosseous nerve). Compression of the latter can produce two distinct clinical syndromes: the radial tunnel syndrome (RTS) and and posterior interosseous nerve syndrome (PINS). It can develop after injury to the elbow, or in RA with tenosynovitis. Involvement of the nerve between the two heads of the supinator at the arcade of Frohse causes weakness of the wrist and digit extensors with sparing of the supinator. EMG findings are in the ECR longus and brevis. The differential diagnosis is tendon rupture. PINS can be caused by a local compressive lesion or repetitive pronation-supination or fracture of the proximal radius. It has a 2:1 male predominance. It manifests as painless weakness without sensory loss of affected muscles, rarely with poorly localized pain or dysesthesias. The hand will deviate radially at the wrist with fingers flexed at the metacarpophalangeal joint without wristdrop. The supinator is spared. NCS excludes partial radial neuropathy. X ray excludes compressive lesions. Therapy is conservative with a long arm splint for immobilization. Surgery can be considered after 12 weeks. RTS is usually seen in the dominant arm of patients with repetitive pronation/supination either on the job or in racket sports. The clinical presentation is aching pain of the elbow and forearm without weakness, but in contrast to PINS there may be numbness in the first dorsal web space. It may be confused with lateral epicondylitis (tennis elbow). Provocative tests (nonspecific) include resisted forearm supination and the middle finger test. The patient extends the elbow and holds the middle finger in extension against a force applied to the dorsum of the hand. Diagnosis can be helped by selective injection into the lateral epicondyle or the radial tunnel. A three month trial of rest, splinting and NISAA's usually is sufficient. Steroid injections and surgery are other resorts.