title: Spontaneous Osteonecrosis of the Knee: A Retrospective Analysis by Using MRI and DEXA.
abstract: OBJECTIVE
  Although there are many etiology and prediction for prognosis of spontaneous osteonecrosis of the knee (SONK) by using radiological examinations, these issue have not been clarified yet. Furthermore, most of the studies evaluated them by only radiological examination such as magnetic resonance imaging (MRI), bone mineral density (BMD) in dual-energy X-ray abosorptiometry (DEXA) or plain X-ray. Therefore, we focused our investigation on the measurements of the affected área in MRI and BMD in DEXA, and whether these results were conected with the cause and prognosis of SONK or not.
  
  
  METHODS
  A consecutive case series of two groups composed of ten osteoporotic patients who were suffering from SONK was considered. Based on the severity or duration of pain, one group was treated with surgical procedure which was unicompartmental knee arthroplasty (UKA), the other received conservative treatment. Both groups underwent DEXA in their distal fêmur and próximal tíbia and all patients who took MRI measured the affected lesion in low and high intensity área on T2 weighted images. This data was analyzed from these areas and units.
  
  
  RESULTS
  Significant decrease in regional boné density of the affected femoral condyle compared to the unaffected side was observed. However, the boné mineral density in the affected side was similar in the non-operative and surgical group. The área of the lesion which showed in both low and high intensity indicated that the operation group was significantly larger than the conservative group on T2 weighted images.
  
  
  CONCLUSIONS
  The cause and prognosis of SONK have a close relationship with the size of the affected lesion and decreased boné mineral density.
authors.affiliation: Igarashi Memorial Hospital, 1-17-23 Tsuchizakiminato-Chuo, Akita 011-0946, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Horikawa
authors.affiliation: Department of Orthopedic Surgery, Akita University Graduate School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
authors.forename: Naohisa
authors.initials: N
authors.lastname: Miyakoshi
authors.affiliation: Department of Orthopedic Surgery, Akita University Graduate School of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Shimada
authors.affiliation: South Akita Orthopedic Clinic, Seiwakai, 96-2 Kaidousita, Syowa-Ookubo, Katagami 018-1401, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kodama
keywords: Bone mineral density (BMD); Dual-energy X-ray absorptiometry (DXA); Magnetic resonance imaging (MRI); Microfracture; Osteoporosis; Spontaneous osteonecrosis of the knee (SONK)