What is a Fabella and Fabella Syndrome?
Fabella is a sesamoid bone (bone in long tendons) found in the lateral Gastrocnemius near its origin. Sutro initially reported this bone and was referred to as ‘‘sesamoide douloureux’’ by Lepoutre in 1929. The occurrence of Fabella is variably reported in different studies depending upon the study population. Fabella can exist in cartilaginous or bony forms and can be unilateral or bilateral. There has been a documented occurrence of Fabello-fibular ligament between Fabella and Fibular head which is thicker and more evident in cases where Fabella is not a bony entity. This ligament is considered atavistic, although it is reported to help stabilize the knees in Kangaroos. Fabella has been reported to be involved in Fabella syndrome. Some existing reports show an increased incidence of intermittent pain due to Fabella in young active athletes without evidence for preponderance for a specific sport. But it remains unclear why only some develop clinical symptoms.
What are the structures and proposed mechanisms involved in Fabella Syndrome?
1. Fabello-Fibular Ligament: Either compressive or tensile forces
2. Gastrocnemius Tendon Compression and irritation of the tendon
3. Femoral condyle Periosteal Inflammation
4. Posterior Capsule Compression of Fabella
5. Common Fibular nerve Compression of neural tissue between Fabella and fibular head
What are the common symptoms of Fabella syndrome?
Most of the patients of Fabella syndrome present with intermittent posterolateral knee pain, whichis mechanical. The pain is accentuated by full knee extension/hyperextension, and localized tenderness results from compression of the Fabella or the Fabello-fibular ligament against its condylar surface. The symptoms persist as a dull ache even at rest. Fabellar bone dimensions have been described as ranging from 0.4 to 2.2 cm in size in symptomatic cases. It has been suggested that a Fabella larger than 1 cm in size requires surgical excision, especially in patients undergoing total knee replacement. The proximity of the Fabella to the common peroneal risks its pathology. The impact of the Fabella bone on the femoral condyle has also been implicated in causing synovial irritation, bone edema and roughening of the articular surfaces
How is Fabella syndrome treated?
A trial of conservative care is recommended before consideration of surgery in children with Fabella syndrome. Conservative management would include analgesic medication, immobilization, activity restriction, steroid injection and manual therapy.
For many adults with Fabella syndrome, however, Fabellectomy has been advised early in the management of painful Fabella in some reports.
Fabella syndrome should be considered an important pathological entity in patients with posterolateral knee pain, especially with hyperlaxity or injuries with or without common Peroneal nerve palsy. The incidence of Fabella syndrome appears to be higher in the Asian population. In light of limited publications about the Fabella syndrome, its function and the consequence of its presence or absence are still unclear. The treatment treating Fabella syndrome includes both non-operative treatment and surgical excision. Even surgical intervention has guarded results, so treatment should be selected after weighing all risks and benefits, and this might be a subject for further research to find out the best possible treatment for Fabella syndrome
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