Osteochondroma - femur

Case contributed by Assoc Prof Frank Gaillard


Medial joint line knee pain.

Patient Data

Age: 50 years
Gender: Male

X-rays of the left knee.


A large posteromedial bony projection is demonstrated involving the distal one quarter of the femoral shaft. It is continuous with the medullary cavity and has an irregular medial margin without large soft tissue component or fracture. Severe narrowing of the medial and patellofemoral joint compartments and marginal osteophyte formations indicate degenerative disease of the knee.

CT of the left knee


A large bilobed exostosis arises from the posteromedial aspect of the distal femoral diaphysis, extending into the metaphyseal region. The medullary cavity of the exostosis is directly continuous with that of the femur and although the cortex is thinned in several areas, it remains intact. 

The exostosis indents and distorts the semimembranosus posteriorly, the sartorius medially, and the vastus medialis anteriorly but there is no soft tissue mass associated with this lesion. No demonstrable cartilage cap. No pathological fracture or periosteal reaction demonstrated.

MRI left knee


There is a bilobed, or two adjacent osteochondromas arising from the left posteromedial femur, measuring approximately 8.8 cm vertically. The proximal end of the lesion commences approximately 14.5 cm superior to the knee joint. The posterior component measures approximately 2.5 cm in diameter, in the medial lesion measures approximately 4 cm. A very thin cartilage cap is present, measures less than 5 mm in thickness.

The medial component protrudes into the vastus medialis, adjacent to the septum between the medial and posterior compartments. It lies just anterior the adductor tendon. The posterior component is adjacent to the popliteal artery where there is no aneurysm. It indents the semimembranosus muscle, separated by a small bursa.

Severe tricompartmental degenerative change is noted in the knee, not fully assessed, but there is extensive osteophyte formation and loss of joint space. Small knee joint effusion and intercondylar synovitis are present. 

Distribution of osteochondromas


Distribution of osteochondromas. Layout and distribution: Frank Gaillard 2012, Line drawing of the skeleton: Patrick Lynch 2006, Creative Common NC-SA-BY

Case Discussion

This case illustrates the typical appearances of large osteochondroma (also known as an osteocartilaginous exostosis) without malignant degeneration or pathological fracture. This lesion has remained asymptomatic for over 2 years, although the patient is soon to have a knee replacement for degenerative joint disease. 

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