Fabella syndrome is a rare cause of posterolateral knee pain which occurs when an accessory ossicle called a " Os Fabella " is the cause of the pain.
Fabella syndrome is a rare cause of posterolateral knee pain which occurs when an accessory ossicle called a " Os Fabella " is the cause of the pain. Although much less common that typical injuries like meniscus tears , ligament injuries and knee osteoarthritis , fabella syndrome can cause irritation and pain, especially during activities like running, squatting or even walking. Given the relatively uncommon nature of the condition, this post seeks to summarize the condition.
When present, the fabella typically lives tucked away inside the lateral head of the gastrocnemius muscle. Think of it a bit like the kneecap — a bone embedded in a tendon — but much smaller and behind the knee instead of in front; however, it doesn’t serve a meaningful function like the patella does. Interestingly, not everyone even has a fabella!
It’s only present in about 20–30% of people overall, though some populations see it much more commonly. In most cases, it stays silent. But when it gets irritated or starts rubbing against the lateral femoral condyle, it can become a real source of pain, a phenomenon termed Fabella Syndrome Lateral knee radiograph demonstrating the presence of Os Fabella (red arrow) Diagnosing fabella syndrome isn’t always straightforward.
Patients usually complain of nagging pain at the back and side of the knee, which tends to flare up with knee extension activities like kicking, jumping, or pushing off during running. On exam , pressing deep into the posterolateral knee can reproduce the pain — sometimes even allowing you to feel a small, firm bump if the fabella is large enough. However, given that the fabella is an incidental finding on most radiographs, diagnosis is not always straightforward.
The presence of a fabella on radiographs and posterolateral knee pain does not guarantee the diagnosis. The right knee MRI showed a fabella with subchondral cyst formation in Coronary view Imaging is necessary to make the diagnosis when combined with the appropriate clinical picture. Plain films can sometimes show the fabella, especially if it’s fully ossified (bone rather than cartilage).
If you are experiencing symptoms that may be related to fabella syndrome, it is important to see a sports medicine physician. Early evaluation and treatment typically lead to better outcomes. Do not ignore pain or symptoms that are limiting your activity.
*This article is for educational purposes only and does not substitute for professional medical advice. Always consult a qualified healthcare provider.*
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