Erbsenbein

Erbsenbein, in anatomy commonly referred to as the pisiform bone, is a small, pea-shaped carpal bone in the human wrist. The term derives from German, where Erbsenbein literally means “pea bone” (Erbse = pea; Bein = bone). It is the smallest of the eight carpal bones and is typically described as a sesamoid bone embedded within the tendon of the flexor carpi ulnaris.

Location and anatomy

The pisiform sits on the anterior (palmar) surface of the wrist, in the proximal row of carpal bones on the ulnar (little finger) side. It articulates with the triquetrum (the other proximal carpal bone on that side) and serves as an attachment and pulley's point for surrounding ligaments and tendons. The bone lies within the tendon of the flexor carpi ulnaris, giving it a specialized role in wrist flexion.

Function

As a sesamoid bone, the pisiform increases the mechanical advantage of the flexor carpi ulnaris, aiding wrist flexion. It also provides attachment points for ligaments, including the pisohamate and pisometacarpal ligaments, which help stabilize the ulnar side of the wrist and the base of the fifth metacarpal.

Clinical significance and variation

Fractures of the pisiform are relatively uncommon but can occur after direct trauma to the ulnar wrist or falls onto an outstretched hand. Diagnosis is typically through imaging, and treatment ranges from immobilization to, rarely, surgical intervention if fragments are displaced or pain persists. Some individuals may have a bipartite pisiform (two bone segments) as a normal anatomic variation.

In summary, Erbsenbein refers to the pisiform bone, a small, pea-shaped structure with a key role in wrist mechanics and stability.