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What Is a Fabella Bone? The Astonishing Anatomy of Fabella Syndrome

The fabella knee bone is a small nodule located directly behind the knee, which occasionally leads to the development of fabella syndrome. As always, Flo’s here to answer all your top questions, including: “What is a fabella?” and “How is fabella syndrome treated?”

Meaning “little bean” in Latin, the fabella is a uniquely mysterious sesamoid bone found at the back of the knee joint, embedded into a tendon. Generally speaking, the fabella is situated at the top of the calf muscle, where the lowest part of the femur bone attaches to the knee. Its primary purpose is to support flexion at the knee. 

Experts estimate that anywhere between 20 to 87 percent of individuals possess a fabella, but don’t necessarily know it. As its name suggests, the fabella bone is tiny – only a centimeter or two in diameter. Comprised mostly of cartilage, it can sometimes ossify or harden, taking on a more typical, bone-like density.

Interestingly enough, humans don’t actually need fabella bones for their knees to exercise a normal range of motion. In fact, the fabella was previously thought to be a lost characteristic, vanishing somewhere along the evolutionary timeline. So why is the fabella back? 

Some experts theorize that perhaps the fabella knee bone never really disappeared at all. Medical advancements over the decades have drastically improved imaging technology and what doctors are able to see. So it’s not that more people are suddenly developing fabellas, but rather that imaging capabilities have prompted a greater awareness of fabella pain.

Producing discomfort at the back of the knee rather than the front, fabella syndrome tends to present itself during certain physical activities. Alternatively, those with fabella syndrome could observe symptoms when their knee is in a particular position, like while sitting cross-legged. They usually worsen when the knee is straightened or extended, encouraging the fabella to press on the end of the femur. This is also true if the fabella happens to interfere with nerves like the common fibular (CF) nerve. Note that some individuals who have a fabella might not encounter fabella syndrome at all. 

Fabella syndrome may worsen over time, especially if the fabella knee bone continues to calcify or rub against the edge of the femur. 

Fabella syndrome is typically marked by feelings of pain or tenderness behind the knee. It’s frequently compared to having gravel inside the knee, or a grating sensation whenever the knee is bent or extended.

Fabella knee patients say discomfort is triggered by one or more physical activities or movement patterns. Since flexing and bending the leg is a contributing factor, squatting, jumping, or cycling can aggravate the pain associated with fabella syndrome. As mentioned above, sitting cross-legged is another culprit, as well as stretching the leg at its end-range.

In some instances, a problematic fabella knee bone could lead to paralysis of the CF nerve, possibly affecting movement in the lower leg. Additionally, fabella syndrome symptoms may appear alongside warning signs of tendinitis or bursitis of the knee.

If you suspect you’ve developed fabella syndrome, your health care provider might suggest seeing a physical therapist or sports medicine specialist. During the visit, they’ll likely run diagnostics tests to assess range of motion and determine exactly which movements are causing pain.

Medical professionals search for the fabella bone by palpating at the back of the knee and checking for swelling or tenderness in the surrounding area. If they believe the fabella is indeed the reason, an ultrasound or magnetic resonance imaging (MRI) is used to confirm their diagnosis. MRIs detect the size of the fabella, while simultaneously pinpointing the location of irritated nerves and/or tissues.

When the fabella bone is creating medical complications or negatively impacting your daily life, there are numerous options to consider trying.

The most common approach to tackling fabella syndrome is physical therapy and manual therapy to help reposition the fabella bone and nearby tissues. Manual therapy (which includes massage or palpation of the knee, calf muscles, and hamstring) serves to alleviate many nagging symptoms. 

Furthermore, studies show that sustained pressure in different directions on fabella-adjacent tissues provide pain relief and enhance range of motion. Even just a few minutes of therapy can be incredibly effective. The practitioner will then ask the patient to try moving their leg in multiple directions to check if fabella pain persists.

If this doesn’t do the trick, your health care provider might recommend regular sessions to reshape soft tissues and alter fabella placement. Other popular remedies include:

  • Physical therapy
  • Injecting local anesthetics or steroids near the fabella site
  • Radial extracorporeal shock wave therapy 
  • Surgical removal of the fabella (i.e., a fabellectomy) 

Several short and long-term complications associated with the fabella bone have been known to arise, such as fracturing or dislocation, and the onset of osteoarthritis.

Although the fabella bone isn’t considered a crucial anatomical structure, those with fabella syndrome may struggle with pain and discomfort behind the knee. It’s usually brought on by repetitive movements like bending or extending the knee.

Luckily, there’s a wide array of treatments available to relieve pain and improve mobility for fabella knee patients. Speak with your health care provider about recurring knee pain so they can perform a proper diagnosis.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3987160/

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6075638/

https://www.jospt.org/doi/pdf/10.2519/jospt.2003.33.1.33

https://www.sciencedirect.com/topics/veterinary-science-and-veterinary-medicine/fabella

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