[Osteochondral fractures of the distal femur]

Chondral or osteochondral avulsions of the lateral distal femur edge after luxation of the patella are well known. Less common are impression fractures of the retropatellar joint or the lateral trochlea. Furthermore, on standard knee X-rays these injuries may not be seen and thus not properly be treated. By presenting our cases we show clinical symptoms, diagnostic pathways and the therapeutic approach for osteochondral fractures of the distal femur.

The first patient had a large osteochondral impression fracture of the lateral femur trochlea and retropatellar surface. The second patient had a chondral depression of the lateral trochlea femoris after kicking a football. The further examinations showed no other knee injuries in the first case, but a rupture of the outer meniscus plus ACL rupture and distortion of the medial collateral complex in the other one.

In both cases the whole degree of the injury was not seen on the standard X-rays, but only on MRI or CT scans. The clinical signs were also not so overwhelming, as both patients could walk with crutches, but suffered from haemarthrosis. Both patients were operated by arthroscopy first with surgery on the meniscus injury and ACL rupture. The impression was revised by an open procedure with elevation of the subchondral spongiosa. In the follow-up examination we saw no dissection of chondral flakes or local necrosis.

Osteochondral lesions of the distal femur can be neglected, as it is an uncommon diagnosis and the radiological signs may not be impressing. The more important is a subtle anamnesis and further diagnostic regime via CT or MRI as it is a prearthrotic injury. Intraoperatively the impression must be elevated or in the case of a dislocation refixed. Further knee injuries have to be detected. In the follow-up one should check for signs of flake dissection or necrosis.