Ulnar nerve entrapment syndromes
Ulnar nerve compression at (or above and below) the elbow, the second most common entrapment neuropathy of the upper extremity, can occur from external pressure at the medial epicondylar groove (synovitis, osteophytes, anesthetized patients with prolonged resting of the elbow on a flat surface), flexion dislocation, and compression at the aponeurosis of the flexor carpi ulnaris or Osborne’s ligament, the so-called cubital tunnel ( Fig. 64.2 ). Cubital tunnel syndrome results in paresthesias in an ulnar nerve distribution (the little finger and ulnar side of the ring finger), weakness in grasping and pinching, catching the little finger on the edge of the pants’ pocket when putting the hand into the pocket (weak interossei and finger adduction), and hypothenar atrophy. Ulnar nerve entrapment is often exacerbated by elbow flexion and by elevating the hand by resting the forearm on the head for 1 minute. Therapy consists of avoidance of prolonged elbow flexion, local steroid injections (in RA), and surgical release in severe cases. Ulnar tunnel syndrome occurs when the ulnar nerve is compressed in Guyon’s canal at the wrist ( Fig. 64.1 ), resulting in symptoms similar to those seen in the cubital tunnel syndrome. Direct pressure over Guyon’s canal causes paresthesias. When ulnar nerve symptoms (weakness more than sensory changes) appear late (months) after trauma to the cubital tunnel, it is referred to as tardy ulnar nerve palsy.