Nerve:  Ulnar

Compartments:  Hypothenar, adductor, interosseous, and central in the hand; anterior in the forearm

Skeletal muscles:  Flexor, abductor, and oponens digiti minimi, adductor pollicis, palmar and dorsal interossei, and lumbricals 3-4 in the hand; flexor carpi ulnaris and one-half the flexor digitorium profundus in the forearm.

Cutaneous distribution:  Skin along the ventro- and dorso-medial hand, medial one-half of digit 4, and all of digit 5. Deficit includes the tips of digits 4-5.

Neuromuscular deficit:  Weakness when flexing and adducting the wrist under resistance.  A “Claw” hand results from dysfunction of intrinsic muscles in the hand (see above). Denervation is accompanied by muscular atrophy, wrist extension and abduction, and extension of digits 4-5, abduction of the thumb, and cutaneous deficits along the distribution of the ulnar nerve. 

Differential diagnosis:  Lesions occurring below the mid-forearm are limited to cutaneous deficits plus dysfunction of the intrinsic muscles of the hand (see above). No motor impairments at the wrist.