The fabella is a small, sesamoid bone located at the back of the knee, often resembling a tiny bean. This bone is not present in everyone, with its occurrence varying significantly among individuals. While often overlooked, the fabella can sometimes be a source of discomfort or pain in the knee region.
Understanding the Fabella
The fabella is a type of sesamoid bone, which means it is a small, independent bone embedded within a tendon, similar to the kneecap (patella). It is found within the lateral head of the gastrocnemius muscle tendon, at the posterolateral aspect of the knee. It forms a direct articulation with the lateral femoral condyle, a rounded prominence at the end of the thigh bone.
The presence of the fabella varies widely, with estimates ranging from 10% to 30% in the general population. It can be present in one knee or both, with bilateral occurrence reported in about 63% to 85% of cases. While its exact function is debated, it is thought to offer a biomechanical advantage, such as reducing friction or modifying pressure, similar to how the patella acts as a pulley to improve muscle efficiency.
Potential Issues Related to the Fabella
The fabella can lead to painful conditions, collectively referred to as fabella syndrome. This syndrome involves pain and tenderness in the posterolateral aspect of the knee, exacerbated by knee extension or activities that increase pressure on the fabella. The pain may stem from irritation or impingement of the fabella against surrounding structures, such as the lateral femoral condyle.
Beyond direct irritation, the fabella’s presence can be associated with other knee problems. It may contribute to osteoarthritis in the knee, particularly if it causes abnormal mechanics or increased localized stress. The fabella can also irritate or impinge upon nearby nerves, leading to symptoms like numbness, tingling, or weakness in the lower leg and foot. Fractures or dislocations of the fabella are also possible, though these are rare occurrences.
Identifying and Addressing Fabella-Related Problems
Diagnosing fabella-related problems begins with a physical examination of the knee. During this examination, a healthcare provider will assess the range of motion, pinpoint areas of tenderness, and evaluate any signs of swelling or instability in the posterolateral knee region. Pain that intensifies with knee extension or direct pressure on the fabella can suggest its involvement.
Imaging techniques confirm the presence of a fabella and assess its relationship to surrounding structures. X-rays can clearly show the fabella’s bony structure and position. Magnetic Resonance Imaging (MRI) provides more detailed images of soft tissues, allowing for evaluation of inflammation in the surrounding tendons, ligaments, or joint capsule, and can help rule out other causes of knee pain. Computed Tomography (CT) scans offer cross-sectional views that can be useful for identifying fractures or dislocations of the fabella.
Treatment for fabella-related pain starts with conservative management. This includes rest from aggravating activities, applying ice to reduce inflammation, and using non-steroidal anti-inflammatory drugs (NSAIDs) to alleviate pain and swelling. Physical therapy can also be beneficial, focusing on strengthening the muscles around the knee and improving flexibility to reduce stress on the fabella. Corticosteroid injections may be administered around the fabella to decrease localized inflammation and provide temporary pain relief.
If conservative approaches do not adequately resolve symptoms, surgical intervention, known as a fabellaectomy (removal of the fabella), may be considered. This procedure is generally reserved for persistent and severe cases where the fabella is definitively identified as the source of pain and other treatments have failed.