Test your knowledge: two anatomical variances.
This week, we’ll discuss 2 radiological and magnetic resonance images. Can you tell the name of these two anatomic variants (in both foot and knee)? And what is the clinical importance of the anatomic variant in the X-ray image (i.e. the foot)
See the answer of this question below the two images!
The first picture represents a lateral view of the knee. You can see an additional bony dot in the popliteal fossa. It is called an os fabella (latin for little bean). It is a small sesamoid bone found in the tendon of the lateral head of the gastrocnemius muscle behind the lateral condyl of the femur. It is a variant of normal anatomy and is represented in 10-30% of the population. It can be mistaken for a loose body or an osteophyte. An osteophyte or loose body is mainly found intra-articular and a fabella is always found extra-articular.
The second image shows an os trigonum. It is found at the dorsal aspect of the talus bone and is an accessory bone, which is found in 2-14% of normal feet. It is oval, round or triangular in shape and arises from a separate ossification center. It is an important cause of dorsal ankle pain in dancers or runners because of the range of motion of plantar flexion. It can cause a plantar flexion block due to impingement of the posterior aspect of the talus between the dorsal tibia and calcaneus. Operative treatment is recommended in professional sport and ballet because of the repetitive impingement of the dorsal talus and os trigonum. Excision of the bony block will often improve motion and eliminate pain.