Fabella syndrome is a uncommon explanation for posterolateral knee ache which happens when an adjunct ossicle known as a “Os Fabella” is the reason for the ache. Though a lot much less frequent that typical accidents like meniscus tears, ligament accidents and knee osteoarthritis, fabella syndrome may cause irritation and ache, particularly throughout actions like operating, squatting and even strolling. Given the comparatively unusual nature of the situation, this submit seeks to summarize the situation.
When current, the fabella sometimes lives tucked away contained in the lateral head of the gastrocnemius muscle (1). Consider it a bit just like the kneecap — a bone embedded in a tendon — however a lot smaller and behind the knee as a substitute of in entrance; nevertheless, it doesn’t serve a significant perform just like the patella does. Curiously, not everybody even has a fabella! It’s solely current in about 20–30% of individuals general, although some populations see it rather more generally. Most often, it stays silent. However when it will get irritated or begins rubbing in opposition to the lateral femoral condyle, it might probably grow to be an actual supply of ache, a phenomenon termed Fabella Syndrome
Lateral knee radiograph demonstrating the presence of Os Fabella (pink arrow)
Diagnosing fabella syndrome isn’t all the time simple. Sufferers often complain of nagging ache on the again and facet of the knee, which tends to flare up with knee extension actions like kicking, leaping, or pushing off throughout operating. On examination, urgent deep into the posterolateral knee can reproduce the ache — generally even permitting you to really feel a small, agency bump if the fabella is massive sufficient. Nonetheless, provided that the fabella is an incidental discovering on most radiographs, prognosis shouldn’t be all the time simple. The presence of a fabella on radiographs and posterolateral knee ache doesn’t assure the prognosis.
The suitable knee MRI confirmed a fabella with subchondral cyst formation in Coronary view (4)
Imaging is important to make the prognosis when mixed with the suitable medical image. Plain movies can generally present the fabella, particularly if it’s absolutely ossified (bone moderately than cartilage) (3). Ultrasound can present a cell or infected fabella though the diagnostic utility shouldn’t be nicely mentioned within the literature. MRI may present comfortable tissue irritation, tendon irritation or cartilaginous modifications, in addition to assist rule out different frequent issues like meniscal tears or ligament accidents.
Therapy often begins conservatively. Exercise modification and relative relaxation, bodily remedy centered on strengthening and adaptability across the knee, and NSAIDs to cut back irritation might be very efficient. In some instances, a focused corticosteroid injection across the fabella sometimes requiring ultrasound steering can dramatically relieve signs (5). Most individuals enhance with this strategy, and inside a couple of weeks to months, they will steadily return to full exercise.
When conservative measures are insufficient to manage signs, surgical excision of the fabella is an possibility. Sadly, there isn’t a literature obtainable to check non-surgical and surgical outcomes. After a brief interval of rehabilitation centered on restoring movement and energy, sufferers usually get again to their sports activities or energetic life with out the nagging knee ache they’d earlier than.
The fabella is a small sesamoid bone behind the lateral knee — not everybody has one.
When symptomatic, it causes posterolateral knee ache, particularly with extension.
MRI is the perfect imaging device for prognosis
Most instances enhance with conservative administration like bodily remedy and injections
- CHARLES J. SUTRO, MAURICE M. POMERANZ, SYDNEY M. SIMON. FABELLA (SESAMOID IN THE LATERAL HEAD OF THE GASTROCNEMIUS). (1935) Archives of Surgical procedure. 30 (5): 777. doi:10.1001/archsurg.1935.01180110048003
- Wikipedia contributors. (2025, February 23). Fabella. In Wikipedia, The Free Encyclopedia. Retrieved 20:32, April 26, 2025, from https://en.wikipedia.org/w/index.php?title=Fabella&oldid=1277186908
- Berthaume MA, Di Federico E, Bull AMJ. Fabella prevalence fee will increase over 150 years, and charges of different sesamoid bones stay fixed: a scientific overview. J Anat. 2019 Jul;235(1):67-79. doi: 10.1111/joa.12994. Epub 2019 Apr 17. PMID: 30994938; PMCID: PMC6579948.
- Weng, Shuo-Po, et al. “Therapy of Fabella syndrome with arthroscopic fabellectomy: a case collection and literature overview.” BMC Musculoskeletal Problems 22 (2021): 1-7.
- Samra, David, et al. “Consequence of Fabellar excision on return to sport and efficiency for an elite athlete with established lateral compartment chondropathy.” Orthopaedic Journal of Sports activities Drugs 9.9 (2021): 23259671211034157.