Topic Overview

Sesamoid Bones of the Hand

General Features

• Small nodular bones embedded within tendons.

• Function → reduce friction, modify pressure, and increase mechanical efficiency of muscles.

• Most common in flexor tendons of thumb.

Clinical Anatomy of Sesamoid Bones

• Normal sites

  • Two sesamoid bones usually present at the head of 1st metacarpal (thumb) in flexor pollicis brevis tendon.

  • One may be present in tendon of adductor pollicis.

  • May also occur at metacarpophalangeal joints of fingers, pisiform is a constant sesamoid in tendon of flexor carpi ulnaris.

• Radiological importance

  • Sesamoid bones may be mistaken for fracture fragments.

• Fractures of sesamoid

  • Painful, especially in thumb (may impair opposition and grip).

• Accessory sesamoids

  • Presence of additional sesamoids is a normal anatomical variation.

Mnemonics for Sesamoid Bones of Hand

“Two in the thumb, one may come”

• Always two at head of 1st metacarpal.

• Sometimes additional one at adductor pollicis tendon.

Facts to Remember

• Pisiform is a constant sesamoid bone.

• Sesamoids are usually located in flexor tendons where pressure is maximum.

• They ossify late, generally around puberty.

• Can help in age estimation if present.

• Important surgically → fractures, sesamoiditis, arthritis of MCP joint of thumb.