There are several muscles in the thumb that allow for movement of the hand and fingers. Three of these muscles, which permit the movement of the little finger, are known collectively as the hypothenar eminence. This name comes from the fact that they structurally resemble the muscles that control thumb motion, called the thenar eminence. The muscles of the hypothenar and thenar eminence, with one exception, initially extend from the same area, the transverse carpal ligament.
The three muscles that constitute the hypothenar eminence are called the abductor digiti minimi, the flexor digiti minimi brevis, and the opponens digiti minimi. The abductor muscle is the most medial, and closest to the ulna, or the arm bone on the same side as the thumb. This muscle is the only one of the group to not originate from the transverse carpal ligament.
Closer to the proximal, or outer, side of the hand, comes the flexor digiti minimi. On the outer end, extending from the transverse carpal ligament to the metacarpal bone of the little finger, is the opponens muscle. The abductor and flexor muscles terminate at the phalanx bone, at the end of the finger.
By having the abductor and opponens muscles insert on opposing sides, at different bones, a greater range of movement is permitted. Aside from moving the little finger itself, the hypothenar eminence helps to move the palm. In conjunction with other palm muscles, the hypothenar muscles help to cup and close the palm, as well as grasp large items.
Much like the thenar muscles, the muscles comprising the hypothenar eminence receive messages from the brain via the ulnar nerve. Some disease states of the hand are associated with this innervation. Should this nerve become damaged or suffer a lesion, the muscles will begin to degrade from disuse. This particular disease state is known as hypothenar atrophy, and can result in a loss of muscular function and mass.
Researchers have noted that the hypothenar eminence is particularly susceptible to loss of sensation, pain, and weakness. This condition is difficult to diagnose, because imaging studies do not always reveal damage. Examinations may not always show a specific cause for this condition, either.
Studies of this condition have revealed that sometimes, small bone fractures can cause problems with the hypothenar eminence. The hamate and pisiform bones, in particular, can create hypothenar conditions. Computerized tomography imaging can sometimes reveal these problems when x-rays cannot. The hypothenar muscles do not insert into these bones, but fractures can lead to a loss of blood flow, or ulnar nerve damage, which will affect the muscles.