The ulnar side of the hand, all of the little finger, and the ulnar side of the ring finger all lose sensation after ulnar nerve injury. The deep branches of the ulnar nerve are motor branches and are sometimes injured by stabbing or penetrating injuries. At the wrist, the ulnar nerve is susceptible to laceration. In the fingers and palm, the superficial branch of the ulnar nerve is also susceptible to laceration.
Etiology In the elbow, the ulnar nerve can be directly traumatized or combined with fracture and dislocation. If the arm is not protected during general anesthesia and is left dangling over the side of the operating table, paralysis may result from compression. In cervical rib or anterior oblique muscle syndrome, the ulnar nerve is most often damaged.
Symptoms 1. Movement Injury on the elbow, ulnar carpal flexors and deep finger flexors are semi-paralyzed and atrophied on the ulnar side, and cannot flex the wrist to the ulnar side and flex the distal phalanges of the ring little finger. When the fingers are placed flat, the little finger cannot climb the table. There was extensive paralysis of the internal muscles of the hand, including the lesser trochanter, the interosseous muscle, the 3rd and 4th earthworm muscles, the internal thumb muscle and the medial head of the short flexor thumb muscle. There is a marked depression between the lesser trochanter and the metacarpal bones. The ring finger and little finger had claw-like deformity. The claw deformity is less severe in supra-elbow injuries; if the injury is distal to the nerve supply of the deep finger flexors, the claw deformity is obvious because the deep finger flexors lose the antagonistic effect of the inner hand muscles, i.e. the ring little finger metacarpophalangeal joint is hyperextended and the interphalangeal joint is flexed. The interphalangeal joint cannot be straightened while flexing the metacarpophalangeal joint.
Due to the antagonistic effect of the radial earthworm muscle, there is no claw deformity or only a slight deformity of the middle index finger. The fingers cannot be abducted internally. The paperclip test is positive. The thumb and index finger cannot be palmarized into a complete “O” shape. The pinch test shows weakness of the two fingers, which is due to paralysis of the inward thumb muscle and inability to stabilize the metacarpophalangeal joint of the thumb. Little finger and thumb pinching disorder. The grip strength of the hand is reduced by about 50% and the flexibility of the hand is lost due to paralysis of the internal hand muscles.
2. Sensation The ulnar side of the hand, all of the little finger, and the ulnar side of the ring finger have lost sensation.
Examination Physical examination is the main focus. Electromyographic examination should be performed if necessary.
Treatment Depending on the injury, decompression, release or anastomosis is performed. To gain length, the ulnar nerve may be moved to the front of the elbow. The ulnar nerve anastomosis is less effective than the radial and median nerves. The radial nerve is mostly motor fibers, the median nerve is mostly sensory fibers, and the ulnar nerve has roughly equal sensory and motor fibers, so the sutures must be accurately aligned and not rotated. Suturing the sensory and motor branches of the ulnar nerve distally is effective. If there is no recovery, the intrinsic extensor muscles of the index and little finger and the superficial flexor muscles of the middle ring finger can be transferred to replace the interosseous and earthworm muscles to improve hand function.