Non-ossifying fibroma

Case contributed by Fabio Macori

Presentation

Knee pain

Patient Data

Gender: Male
x_ray

The x-ray shows at the distal femur, with eccentric location, the presence of an ovoid-shape, well-defined, formation with sharply defined sclerotic margins in suspicion of a non-ossifying fibroma

Case Discussion

Occasional finding discovered during a routinary knee x-ray requested for pain.

Jaffe and Lichtenstein were the first authors to describe the non-ossifying fibroma in 1942. They described several characteristics including:

- the NOF lesion is eccentric in location in the metaphysis and will typically have a sclerotic rim and appear multiloculated

- the most common location is the distal femur (followed by the distal lateral tibia and proximal medial tibia).

There are different hypothesis why the distal femur is the most common location of NOFs, one of these suggest that the reason is due to the particular anatomy of the bone because its posterior cortex is thin with a concave shape of the posterior condyles (Goldin et al - see references) and because in the distal femur NOFs typically arise as ‘tug lesions’ at the origin of the medial head of the gastrocnemius where its insertion being broader and thicker with a more transverse shape than the lateral gastrocnemius.

The case presented shows both of the main, typical, findings previously described.

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