Because it is due to compression of a motor nerve, patients may compare the pain to a muscle cramp, which is deep and aching in nature. Typically the patient will complain of poorly localized pain over the lateral aspect of the elbow, which may radiate up or down the arm. With repetitive forearm supination and pronation, the fibrous edge of the radial wrist extensor (the extensor carpi radialis brevis) and the fibrous upper border of the supinator muscle have a scissoring action on the nerve which leads to intermittent PIN compression. That is, the compression is intermittent and dependent upon muscular action. In many instances there is a dynamic entrapment of the nerve. It is most commonly entrapped by the fibrous upper edge of the supinator muscle as it travels through the muscle. The PIN branch may be entrapped by up to 5 separate structures. This sensory branch is not compressed since it takes off prior to the site of compression, hence sensation remains normal. The superficial sensory branch remains on the lateral border of the forearm, where it ultimately supplies sensation to the back of the thumb and the 1st web space. The nerve sequentially innervates the extensor muscles of the wrist, fingers and thumb. The PIN then travels from the anterior aspect of the elbow, through the supinator muscle at the radial head level to emerge on the back part of the upper forearm. The radial nerve divides into it’s two terminal branches, a motor branch (PIN) and a superficial sensory branch just before the elbow. Although the same nerve is compressed, the clinical presentation may be different, and merely represent two ends of the spectrum of PIN compression. Radial tunnel syndrome conversely has no sensory nor motor loss. In this case, the presenting symptoms are due to weakness and/or paralysis of the extensor muscles, which results in a wrist or finger drop. Posterior Interosseous Nerve Entrapment also involves the PIN. This nerve branch supplies all of the forearm muscles which are responsible for extension of the fingers, wrist and thumb. The nerve involved is the posterior interosseous nerve (PIN), which is the motor branch of the radial nerve at the elbow. It may seem paradoxical that compression of a motor nerve can cause pain, since it was originally thought that only the sensory nerves contained pain fibers, but this is now well accepted. It is especially of interest in that it can mimic tennis elbow, or lateral epicondylitis. In fact, the main symptom is that of proximal elbow pain. Radial tunnel syndrome on the other hand, does not result in any numbness nor tingling. Cubital tunnel syndrome leads to similar symptoms in the small and ring fingers. Carpal tunnel syndrome initially results in numbness and tingling that affects the thumb, index and middle fingers. This syndrome is much less common and lesser known than median nerve compression at the wrist (carpal tunnel syndrome) and ulnar nerve compression at the elbow (cubital tunnel syndrome). Entrapment of a motor nerve can result in muscle weakness or paralysis, but it some instances it can lead to muscular pain.Įntrapment of the motor branch of the radial nerve at the elbow can result in a constellation of symptoms which has been termed Radial Tunnel Syndrome. Entrapment or compression of a sensory nerve results in numbness and/or tingling of the fingers. The PIN then travels dorsally between a number of large muscles to reach the back of the upper forearm, and innervates all of the muscles that raise (extend) the wrist, fingers and thumb. Just past the elbow, the radial nerve then divides in to a large sensory branch (the superficial radial nerve) that supplies sensation to the back of the hand over the thumb web, and a motor branch called the posterior interosseous nerve (PIN). ![]() The radial nerve arises from a large plexus of nerves in the neck (the brachial plexus), winds around the back of the upper arm (humerus) to lie in front of the elbow. There are 3 major nerves that supply the muscles of the hand and forearm as well as sensation to the hand: the median, ulnar and radial nerves.
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