12/01/2024
FABELLA BONE, AN EVOLUTIONARY ENIGMA 🪷
The fabella is a small sesamoid bone found in some mammals embedded in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyle of the femur. It is an accessory bone, an anatomical variation present in 39% of humans. Rarely, there are two or three of these bones (fabella bi- or tripartita). It can be mistaken for a loose body or osteophyte. The word fabella is a Latin diminutive of faba 'bean'.
In humans, it is more common in men than women, older individuals compared to younger, and there is high regional variation, with fabellae being most common in people living in Asia and Oceania and least common in people living in North America and Africa. Bilateral cases (one per knee) are more common than unilateral ones (one per individual), and within individual cases, fabellae are equally likely to be present in right or left knees. Taken together, these data suggest the ability to form a fabella may be genetically controlled, but fabella ossification may be environmentally controlled.
Although the fabella seems to have disappeared with the evolution of Hominidae, it reappeared in humans sometime after they diverged from chimpanzees. It is unknown whether it reappeared soon after this divergence, 5–7 million years ago, or more recently in human evolution.
"The fabella can lead to posterolateral knee pain either due to cartilage softening (chondromalacia fabellae) or other osteoarthritic changes on its articular surface."
🟣 Some interesting facts about the fabella
🔖 Little Bone, Big Impact: The fabella is a small, sesamoid bone located behind the knee, embedded within the tendon of the lateral head of the gastrocnemius muscle.
🔖 Not Everyone Has It: While not everyone has a fabella, its presence varies widely among individuals. Some people have one in each knee, some have them in both, and others may not have them at all.
🔖 Evolutionary Enigma: The fabella is considered a vestigial structure, meaning it has lost its original function through evolution. Its purpose in the human body is not entirely clear, but it's believed to be related to the function of the knee joint and surrounding muscles.
🔖 Varied Prevalence: The occurrence of the fabella has been reported to be more common in certain populations or age groups. Studies suggest that its prevalence has increased over the years.
🔖 Historical Presence: The fabella has been found in ancient human remains, indicating that it's not a recent development in human anatomy. However, its prevalence and significance have changed over time.
🔖 Role in Knee Issues: In some cases, the presence of a fabella has been associated with knee pain or complications. It can contribute to conditions like fabella syndrome, where irritation or impingement of the fabella causes discomfort.
🔖 Imaging Challenges: Detecting the fabella can be challenging through standard X-rays, and more advanced imaging techniques like MRI or CT scans are often needed for accurate identification.
🔖 Orthopedic Considerations: Surgeons may encounter the fabella during knee surgeries, and its presence can influence the approach taken in certain procedures.
🔖 Individual Anatomical Variation: The size and shape of the fabella can vary significantly among individuals, adding to the complexity of its study and understanding.
🔖 Ongoing Research: Despite being known for centuries, the fabella continues to be a subject of ongoing research, with scientists and anatomists delving deeper into its evolutionary history and potential roles in musculoskeletal health.
Dr Messum Raza Alvi
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