大腿骨内側顆から外側顆へと移動した膝関節区域性移動性骨萎縮症の1例

Regional Migratory Osteoporosis of the Knee Migrated from Femoral Medial Condyle to Lateral Condyle. Case Report

　一過性骨萎縮症は数カ月で治癒するself-limitedな疾患である．他関節に病変部位が移動するものは区域性移動性骨萎縮症と呼ばれる．今回われわれは膝関節の大腿骨内顆に発生し病変が外顆へ移動した区域性移動性骨萎縮症を経験した．症例は50歳，男性．階段を降下中に外傷なく右膝痛が出現した．単純X線像において大腿骨内顆に骨萎縮像，MRIにおいて大腿骨内顆にT1強調像で低輝度，T2強調像でやや高輝度の領域を認めた．下肢免荷装具と消炎鎮痛薬を処方して経過観察を行った．2カ月後，内顆の圧痛は消失したが外顆に圧痛を認めた．MRIでは内顆の輝度変化はほぼ消失していたが，外顆にT1強調像で低輝度，脂肪抑制像で高輝度の領域を認めた．8カ月後のMRIでは輝度変化は消失し，単純X線でも骨萎縮像は消失した．骨萎縮症は保存治療で治癒する疾患であるが，区域性移動性骨萎縮症へ移行することもあるため慎重な観察が必要である．

　Transient osteoporosis is a self-limited disorder that usually heals in several months. Migration to another joint is called regional migratory osteoporosis. We report a case of regional migratory osteoporosis of the knee migrating from the femoral medial condyle to the lateral condyle. A 50-year-old man suffered from right knee pain without any history of injury. Radiographic examination showed an osteopenia of the femoral medial condyle. An MRI scan showed a low-intensity area on T1-weighted images and a mild high-intensity area on T2-weighted images. We treated the patient with protected weight-bearing and a nonsteroidal anti-inflammatory drug. Two months later, the tenderness at the femoral medial condyle had disappeared, but the patient complained of tenderness at the femoral lateral condyle. An MRI scan showed an almost normal intensity in the femoral medial condyle region, but a low-intensity area was visible on the T1-weighted images and a high-intensity area was visible on fat suppression images of the lateral femoral condyle. Eight months later, the abnormal intensities on the MRI scans and the radiographic examinations had returned to normal.