title: Subchondral fracture of the femoral head after acetabular fracture: a case report.
abstract: BACKGROUND
  Preventing post-traumatic osteoarthritis is a challenging problem following acetabular fracture. Progressive osteoarthritis is considered to be caused by an irregular articular surface of the acetabular roof or cartilage injury, but little is known about the pathogenesis of collapse of the femoral head after acetabular fracture. We report a case of post-traumatic osteoarthritis after acetabular fracture in which subchondral fracture of the femoral head contributed to the progressive collapse of the femoral head and osteoarthritis. To the best of our knowledge, there has been no previous report of subchondral fracture of the femoral head after acetabular fracture.
  
  
  METHODS
  A 58-year-old Japanese man fell from a ladder. He was diagnosed with a left acetabular fracture, which was managed conservatively. He developed left coxalgia six months after injury and was seen at our institution one year after the onset of pain. The left acetabular fracture had fused, but his left femoral head had collapsed. The images at the time of injury showed a fracture of the acetabular roof, and an approximately 2mm step-off existed in the articular surface. Retrospective evaluation of the plain radiographs and computed tomography images showed that his femoral head had progressively collapsed. Our patient underwent total hip arthroplasty. Histopathologic findings demonstrated that the collapse of his femoral head was caused by a subchondral fracture of his femoral head.
  
  
  CONCLUSIONS
  Our experience with this case indicates that in addition to post-traumatic osteonecrosis, subchondral fracture may need to be considered in cases with progressive collapse of the femoral head after acetabular fracture.
authors.forename: Keiichiro
authors.initials: K
authors.lastname: Iida
authors.affiliation: Department of Orthopaedic Surgery, Faculty of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. hamachan@ortho.med.kyushu-u.ac.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Hamai
authors.forename: Takuaki
authors.initials: T
authors.lastname: Yamamoto
authors.forename: Yasuharu
authors.initials: Y
authors.lastname: Nakashima
authors.forename: Goro
authors.initials: G
authors.lastname: Motomura
authors.forename: Masanobu
authors.initials: M
authors.lastname: Ohishi
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Karasuyama
authors.forename: Yukihide
authors.initials: Y
authors.lastname: Iwamoto
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000293:injuries*; D019644:Arthroplasty, Replacement, Hip; D005270:Femur Head / Q000000981:diagnostic imaging / Q000293:injuries*; D006620:Hip Fractures / Q000150:complications / Q000000981:diagnostic imaging*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000000981:diagnostic imaging / Q000209:etiology*; D014057:Tomography, X-Ray Computed