Imaging description

There are several sesamoid bones that we expect to see in most, if not all, patients, as well as other variants that may also be detected. The largest and best known sesamoid bone is the patella, which is part of the extensor mechanism of the knee (Figures 85.1–85.4).

In the foot, there are typically two first hallux sesamoid bones within the two heads of the flexor hallucis brevis tendon, forming part of the first metatarsophalangeal joint capsule along the plantar surface of the first metatarsal head (Figures 85.5–85.9) [1]. The tibial sesamoid is medial and the fibular sesamoid lies laterally. Additionally, the os peroneum may be seen along the lateral aspect of the midfoot within the distal peroneus longus tendon (Figures 85.10–85.12).

Each hand typically has five sesamoid bones: two at the first metacarpophalangeal (MCP) joint, one each at the second and fifth MCP joints, and one at the first interphalangeal joint (Figures 85.13 and 85.14).

Importance

Sesamoids are accessory ossific structures that are contained within a tendon or joint capsule and reduce friction during flexion and extension as they slide over adjacent structures. In distinction to accessory ossicles, sesamoids form from their own ossification center. Like accessory ossicles, the importance of sesamoids is recognizing their normal and variant appearances that maybe mimic or hide acute pathology.