Compression of the ‘ulnar nerve’ usually at the level of the elbow. This nerve supplies power to some muscles of the hand (interossei muscles) and is also responsible for the sensation in the little finger and half of the ring finger. At the elbow, it emerges from the depth at the inner side of the upper arm just above the elbow and passes under a flat band (Struther´s arcade). It then passes around the elbow in a groove between the main elbow bone (olecranon – that is where you rest your arm on when bending it) and another bone just to the inner side (medial epicondyle). It is this point that gives a tingling sensation in the ring and little finger when hitting the elbow (‘funny bone’). The nerve then passes between the muscles (two heads of flexor carpi ulnaris muscle) back into the depth of the forearm. The nerve can be trapped at all three points but is most commonly trapped where it passes around the elbow. In very rare cases the nerve can be trapped at the level of the wrist (Guyon’s canal). Possible causes include direct injuries or leaning on the nerve when resting the elbow on a hard surface over a long period of time. In many patients no cause can be found. Symptoms can start many years after an elbow injury.
Patients might notice numbness, a tingling sensation or pain in the little and half of the ring finger. In more severe cases patients might notice weakness of the grip of the hand.
Numbness of the little and half of the ring finger.
Wartenberg’s sign: An early sign in ulnar nerve syndrome. The little finger sticks slightly out at rest in comparison to the other side. This is because of a weakness of one of the hand muscles (3rd palmar interosseus muscle)
Froment’s sign: When trying to grasp a sheet of paper between the thumb and index finger, the first half of the thumb (proximal phalanx) extends and the tip (distal phalanx) bends. This is due to weakness of the muscle which presses the thumb against the index finger (adductor pollicis muscle).
Claw deformity: In severe cases, the hand goes into a claw position.