The human wrist is a complex structure composed of eight small bones known as carpal bones. These bones are arranged into two rows, facilitating a wide range of motion and providing stability to the hand. Among these carpal bones is the pisiform, a small but significant bone that plays an important role in wrist function.
Finding the Pisiform Bone
The pisiform bone is located on the ulnar side of the wrist, near your pinky finger. It sits near the base of the palm, forming a noticeable bump on the front surface of the wrist. Due to its superficial position, the pisiform is one of the easiest carpal bones to locate and feel.
To find your own pisiform bone, extend your arm with your palm facing upwards. Gently feel the area at the base of your palm, just below the crease of your wrist, on the pinky finger side. You should be able to feel a small, pea-sized, round bone that can often be moved slightly under the skin. This palpable bone is your pisiform.
The Pisiform’s Unique Anatomy and Function
The pisiform is unique among carpal bones as a sesamoid bone. Sesamoid bones are small bones embedded within a tendon, rather than directly articulating with other bones through a joint.
The pisiform is embedded within the tendon of the flexor carpi ulnaris (FCU) muscle, a muscle responsible for flexing and adducting the wrist. This anatomical arrangement allows the pisiform to act as a pulley for the FCU tendon, increasing its mechanical advantage. This enhances the strength of wrist flexion and ulnar deviation, making gripping and hand motions more efficient. The pisiform articulates solely with the triquetrum, another carpal bone in the proximal row, but it does not directly form part of the main wrist joint.
When the Pisiform Causes Problems
The pisiform bone can be involved in various conditions that cause wrist pain and dysfunction. Direct trauma, such as falling onto an outstretched hand, can lead to a pisiform fracture. Symptoms include localized pain, swelling on the pinky side of the wrist, and tenderness, often increasing with wrist movement. These fractures are rare and can be difficult to diagnose due to the bone’s small size and position.
Another potential issue is pisotriquetral arthritis, which involves inflammation of the joint between the pisiform and the triquetrum. This condition causes pain on the ulnar side, especially during wrist flexion and ulnar deviation.
Additionally, the flexor carpi ulnaris tendon can become inflamed, leading to tendinitis. FCU tendinitis causes pain and tenderness on the underside of the wrist, particularly when flexing or rotating the wrist, sometimes with a crackling sound or feeling.