[Tumor-like bone lesions of the forearm after karate training]

Differentiation between malignant bone tumors and tumor-like lesions after repetitive microtrauma following sport activities can be difficult just using radiographic methods.

We present the case of a fifteen year old karate fighter, who was examined by imaging diagnostics because of a progressive swelling and pain in the distal right forearm.

A tumor-like appearance with bone mass formation in the x-ray, an enhancement in the surrounding tissue shown in the MRI and an increased activity in the bone scintigraphy made the diagnosis of an osteosarcoma very likely. Blood tests were not helpful. Only the evaluation of a bone biopsy could demonstrate hypertrophic reparative bone formation after multiple osseous microtrauma. Cast immobilisation reduced the osseous alteration. With the start of the training the swelling reappeared again but then finally vanished after modifying the training technique.

The case demonstrates that even modern imaging techniques cannot always distinguish between tumor and tumor-like lesions caused by sports. It also stresses the importance of a correct technique in sports like karate.