Objective: Recently, Dr. Yamamoto suggested that the cause of idiopathic osteonecrosis of the knee results from an insufficiency fracture. He showed that the necrotic lesion of the knee exists peripheral to the fracture line by using pathological methods. It appears that osteoporosis is related to spontaneous osteonecrosis of the knee (SONK). Therefore, we examined the bone mineral density (BMD) of patients with SONK for underlying osteoporosis.
Patients and Methods: The study subjects comprised 50 patients treated in our hospital over a five-year period from April 2007 to April 2012. The age of the patients were 50-89 years old (mean age 71.0 years), with there being eight males and 42 females. There were 41 patients with pathological changes in the medial femoral condyle, and nine patients with changes to the medial tibial plateau. These patients underwent BMD examinations of the vertebral column and femur with dual energy x-ray absorptiometry. They were all tested within six months after the onset of this disease, and in 17 cases, we examined the tibial plateau bone mineral density.
Results: The rate of osteoporosis of these patients was 28%, using BMD, with there being only one male patient affected. In addition, 38% were considered osteoporotic with the use of femur BMD, with only female subjects being affected. The tibial plateau BMD of these patients were slightly lower than those of osteoarthritic patients.
Conclusions: The ratio of osteoporosis in patients with SONK was higher than that of unaffected persons. In our study, male patients with SONK rarely had underlying osteoporosis. The use of BMD in patients with SONK may be a useful adjunct for assessing the underlying disease in affected patients.
