title: Arthrographic indicators for decision making about femoral varus osteotomy in Legg-Calvé-Perthes disease.
abstract: OBJECTIVE
  There is not always a good outcome after a femoral varus osteotomy (FVO) in those with Legg-Calvé-Perthes disease (LCPD), even when the severity warrants surgical treatment. The purpose of this study was to find arthrographic indicators for decision making regarding the likely surgical outcome of a FVO.
  
  
  METHODS
  We used an image of an abduction position during preoperative arthrography under general anesthesia that simulated the post-operative relationship between the femoral head and the acetabulum. In the image, we defined two indicators of how deeply the deformed epiphysis was contained within the acetabulum: an acetabular head index in abduction and an epiphyseal slip-in index. Finding the contact point between the top of epiphysis and acetabulum was the key for the epiphyseal slip-in index measurement. In 37 patients (38 hips) who underwent FVOs based on our inclusion criteria, these two indices were measured retrospectively and were analyzed for a correlation with surgical outcome. Surgical outcome was evaluated using a combination of three factors: sphericity of the femoral head (Stulberg's classification), acetabular cover (acetabular head index), and the slope of acetabular roof.
  
  
  RESULTS
  The outcome was acceptable in 20 hips (52.6%) and unacceptable in18 hips (47.4%). There was a statistically significance difference in epiphyseal slip-in index between the acceptable group (21.9 +/- 2.8%) and the unacceptable group (15.0 +/- 4.4%) (P < 0.0001). An index of 20% or more determined a safe zone for predicting an acceptable outcome with 80% sensitivity, 89% specificity, and a 7.2 likelihood ratio. However, the acetabular head index in abduction showed no such statistical significance.
  
  
  CONCLUSIONS
  In this study, we found that the epiphyseal slip-in index was a reliable indicator for predicting the effectiveness of a FVO. It is worth measuring this index when a surgeon is considering a FVO for a patient with severe LCPD. (Level of Evidence Level III.).
authors.affiliation: Division of Orthopaedic Surgery, Chiba Children's Hospital, 579-1 Heta-chou, Midori-ku, Chiba City, Chiba, 266-0007, Japan, kame-cch@kje.biglobe.ne.jp.
authors.forename: Makoto
authors.initials: M
authors.lastname: Kamegaya
authors.forename: Takashi
authors.initials: T
authors.lastname: Saisu
authors.forename: Makoto
authors.initials: M
authors.lastname: Takazawa
authors.forename: Junichi
authors.initials: J
authors.lastname: Nakamura