fabellar

Fabellar is an adjective relating to the fabella, a small sesamoid bone located within the tendon of the gastrocnemius muscle behind the knee. The fabella can exist as a separate ossified bone or as cartilaginous material that ossifies later, and its presence is variable among humans and other mammals.

Anatomically, the fabella typically lies in the posterolateral aspect of the knee, within the tendon of the lateral head of the gastrocnemius. It may articulate with a small facet on the lateral femoral condyle or be separated by cartilage. In many individuals the fabella is asymptomatic, but it can become clinically relevant if it enlarges, fractures, or contributes to posterolateral knee pain or impingement, especially after injury or knee arthroplasty. Radiographic, computed tomographic, and magnetic resonance imaging can detect the fabella and any associated secondary changes such as osteophyte formation or effusion.

Development and prevalence of the fabella vary widely. It typically develops from secondary ossification centers in the tendon during late adolescence or early adulthood. Prevalence is population-dependent and influenced by imaging modality; some studies report the fabella as present in a minority of adults, while others note it in a substantial portion of individuals or in bilateral form.

Clinical relevance includes consideration during knee surgery, radiologic interpretation, and the differential diagnosis of posterolateral knee pain. Rare complications include fabellar fracture or inflammatory reactions. The term fabellar derives from the Latin fabella, meaning little bean, reflecting the bone’s small, bean-like shape.

See also: fabella, knee anatomy, sesamoid bones.