The pisiform is a bone in the human hand located in the wrist. It is also referred to as the lentiform bone. It is part of a bone cluster called the carpus, which includes several other bones such as the triquetrum, scaphoid and lunate. It is the outermost bone of the carpus, and is located below the pinky finger on each hand.
More specifically, it is located where the ulna, which is the forearm's inner bone that meets up with the carpus cluster. The bone is about the size and shape of a pea — pisiform is Latin for "pea-shaped." Although the bone is very small, it is still a little bit larger than the smallest bone in the body, the stirrup bone located in the ear.
The pisiform is a sesamoid bone, which means it is located within a tendon. In humans most sesamoid bones are found in the hand, foot or knee and they help to increase flexibility and movement. This bone is unique to other wrist bones in that it does not work with other bones in the joints of the wrist. Its sole function seems to be to increase torque and rotation in the wrist and the hand.
The pisiform is rarely fractured in hand injuries. More often other bones in the carpus and proximal row are broken in accidents. Breaks in the pisiform are usually linear fractures and happen most often when the bone is struck directly. Other hand injuries and fractures are usually present when the pisiform is broken. This can lead to injuries of the pisiform bone being overlooked or misdiagnosed, as they are so rare that they are sometimes missed completely by doctors who are focused on more common bone breaks.
Effects of the bone break can be nerve or ligament damage in the surrounding area. Injuries in the hand may also lead to the bone being dislocated, although this is also uncommon. When the bone is injured or broken, wrist and grip strength can be effected.
Often with a break of this bone, treatment includes completely excising it. Leaving the broken bone in the hand usually leads to chronic hand and wrist pain. After the bone is excised the pain usually goes away, and side effects to the removal are marginal. While the wrist, hand and grip strength are adversely effected by its removal, the difference between the wrist with the bone or without without it is usually nominal.