LAUSR

S esamoid bones are small ossicles located where tendons pass over a joint. Their name is related to their appearance, resembling the oval seeds of the plant “Sesamum indicum.” The biomechanical role of sesamoids is not completely understood, but it seems that they reduce friction, protect tendons, and give support to joints. Usually, there are 5 sesamoid bones in the hand, mainly localized at the palmar surface of metacarpophalangeal (MCP) joint. In almost 100% of the population there are 2 sesamoids at the MCP joint of the thumb. Less common sesamoid bones are located at the interphalangeal joint of the thumb (53%), at the MCP joint of the index finger (43.4%), and at the MCP joint of the small finger (66.7%). Exceptionally, sesamoid bones may be found in other MCP joints and interphalangeal joints. Bipartite sesamoid bones were found in 0.6% to 6% of cadaveric hands. The radial sesamoid bone of the thumb MCP joint is embedded within the adductor pollicis tendon, whereas the ulnar one lies inside the flexor pollicis brevis tendon. The two sesamoid bones are connected to the palmar plate and play an important role in joint stability, limiting hyperextension. The index sesamoid bone is frequently located on the radial aspect of the MCP joint, whereas the little finger sesamoid bone is on the ulnar side of the joint. Disorders of hand sesamoid bones are mainly posttraumatic and can be seen in joint sprains, at the MCP joint of the thumb, or in direct trauma such as during falls on MCP joints of other fingers. Because of the sesamoid bones’ small size and superposition of the ossicles with the adjacent bones, sesamoid bone fractures are difficult to detect on standard radiographs. Ultrasound (US) can show radiographically occult fractures. We present a retrospective review of 13 patients with fractures of sesamoid bones of the hand detected by US.