[Core decompression in Ahlbäck's disease. Follow-up and therapy control using MR tomography]

Clinically suspected spontaneous osteonecrosis of the knee (Ahlbäck's disease) was confirmed by MR imaging and subsequent histology in 4 male patients with sudden onset of severe knee pain. The first typical radiological sign for osteonecrosis--flattening of the affected femoral condyle--was seen in no case. All patients were treated surgically by extraarticular drilling for core decompression and were delivered from the complained severe knee pain immediately after surgery. The healing process of early osteonecrosis could be confirmed by the normalisation of bone marrow signal in MR imaging (3 to 15 months follow-up). Core decompression seems to be an effective treatment in early osteonecrosis of femoral condyles. MR imaging is the most sensitive method for early diagnosis of osteonecrosis and for preoperative planning as well as a helpful tool for a non-invasive postoperative follow-up.