A case report of a fingerlike meniscal exostosis

The menisci are intra-articular fibrocartilagenous structures that optimize the joint function. They have several functions. Meniscal malformations are rare and different in shape. The most common are classified in public and known classifications, but some are very rare like finger like exostosis, so it is useful to highlight these rare malformations, that helps in the development of typing and classification, and may explain some unclear mechanisms of injuries.

We know that meniscal tears in young people usually result from clear mechanical causes, like twisting or direct trauma, so we always need a cause, but when your patient does not explain a clear movement or mechanical trauma, you will ask and ask to conclude why. Yes, keep in mind that; it may be caused by a very rare congenital malformation.

A 20 years old male patient presented with a history of left knee pain for 6 months. MRI revealed a horizontal tear with abnormal thickness in the posterior horn of the lateral meniscus. The primary arthroscopic examination discovered a horizontal tear in the PHLM with atypical downward directed fingerlike exostosis. By using an arthroscopic hock, grasper and scissors, the exostosis was removed, and the nearby tear was smoothed with the shaver.

Diagnosis of finger like exostosis is challenging and needs strong clinical suspicion because most of the time, it is not predictable and MRI signs may lead to unclear differential diagnosis. The presence of exostosis give a causative explanation of PHLM horizontal tear especially in absence of clear twisting or direct trauma. It may increase the forward directed pull forces of the nearest part of the meniscus during normal gait and gym exercises.

Fingerlike exostosis and other meniscal malformations should be in mind as rare cases. They may explain the presence of tears in young patients with no clear trauma.