MRI - Knee joint
Axial PD
Axial PD SPAIR
What is the incidental finding in this patient presenting with acute knee injury?
Osteochondroma of the posteromedial tibia
The cartilage cap on this osteochondroma measures 6mm. What level of cartilage thickness would raise the suspicion of malignant transformation into an chondrosarcoma?
Greater than 15mm thickness
Is this osteochondroma involving any local structures?
Yes. The semimembranosus tendon inserts 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 a friction response or if it relates to the patient's presenting acute knee injury. There is no local neurovascular impingement.
Bonus Geek Question! What classic sign related to the patent's acute ACL injury (and most famous on plain radiography) is visible at the lateral aspect of the knee?
Segond fracture avulsion of the anterolateral knee capsule.
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.