Case contributed by Andrew Dixon
Diagnosis certain


Incidental finding on a scan performed for an acute ACL rupture.

Patient Data

Age: 20 years
Gender: Male

Knee joint


Focal bony growth from the posteromedial aspect of the proximal tibia which is continuous with the medullary cavity and has a 6mm thickness cartilaginous cap. No adjacent soft-tissue abnormality. The appearance is consistent with an osteochondroma without features of malignant transformation. The lesion does not cause any local neurovascular impingement, however the semimembranosus tendon does insert into the upper aspect of the lesion and the gracilis and semitendinosus tendons are contacted as they traverse past the lesion. It is difficult to know whether the small amount of fluid within the pes anserine bursa is due to friction or if it relates to the patient's presenting acute knee injury. 

For those with a keen eye, also visible on these selected images is a small avulsed bone fragment from the anterolateral tibial at the capsular insertion consistent with Segond fracture avulsion and a partial tear of the soleus insertion onto the posterior aspect of the fibula. 

Case Discussion

Typical MRI appearance of an osteochondroma with a thin cartilaginous cap. There is local contact of two of the pes anserine tendons and distortion of the semimebranosus tendon insertion, but there is no neurovascular impingement. This was an incidental finding in a young adult presenting with an acute ACL tear with Segond fracture

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