title: [Calculation of articular surface area of osteonecrosis and its application in predicting collapse of the femoral head].
abstract: OBJECTIVE
  To explore the program for calculating the necrotic articular surface area (NASA) and the ratio of NASA to whole articular surface area (WASA) of osteonecrosis of the femoral head (ONFH), to verify the accuracy of this calculation and to predict the collapse of the femoral head clinically using this program.
  
  
  METHODS
  From June 2001 to June 2003, The specimens of the necrotic femoral head from eight patients (13 hips) were obtained by total hip arthroplasty. The magnetic resonance imaging (MRI) was taken in all patients before operation. According to a series of T1-weight pictures, the NASA and the ratio of NASA to WASA were calculated by designing program. The specimens of the necrotic femoral head were sawed into lays similar to MRI pictures using the coordinate paper stick on the auricular surface, the data processing were done by analytic instrument for pictures. The data of both were analyzed statistically by software SPSS 10.0 edition. The NASA and the ratio of NASA to WASA were calculated on MRI in ARCO Stage I, II 16 patients (25 hips) with non-operation. Follow-up was done to the patients with collapse of the femoral head and to the patients with no collapse for at least 24 months. The data were compared in collapse group and non-collapse group.
  
  
  RESULTS
  There were no significant differences between MRI pictures calculation and specimens measurement (NASA: 0. 412, ratio of NASA to WASA: 0.812, P>0.05). Of the 25 hips followed up, collapse occurred in 17 hips. NASA was 31.06+/-8.10 cm2, (95% CI. 26.58 to 35.55), the ratio of NASA to WASA was 58.91%+/-15.11%, (95% CI: 51.14 to 66. 68). No collapse appeared in 8 hips. NASA was 14.16+/-9.32 cm2 (95% CI: 6.04 to 21. 95), the ratio of NASA to WASA was 29.48%+/-19.76% (95% CI: 12.97 to 45.99). The ratio in the patients with collapse was beyond 33%.
  
  
  CONCLUSIONS
  The NASA and the ratio of NASA to WASA in patients with ONFH can be accurately calculated with the MRI pictures. The possibility of collapse can be predicted by this method. As it is complicated in operation, improvement should be made in order to put it into clinical use.
authors.affiliation: Center for Osteonecrosis and Joint-Preserving & Reconstruction, China-Japan Friendship Hospital, Beijing, 100029, P. R. China.
authors.forename: Fengchao
authors.initials: F
authors.lastname: Zhao
authors.forename: Zirong
authors.initials: Z
authors.lastname: Li
authors.forename: Nianfei
authors.initials: N
authors.lastname: Zhang
authors.forename: Zhencai
authors.initials: Z
authors.lastname: Shi
authors.forename: Xuezhe
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000328:Adult; D019644:Arthroplasty, Replacement, Hip; D005260:Female; D005270:Femur Head / Q000473:pathology*; D005271:Femur Head Necrosis / Q000150:complications / Q000473:pathology* / Q000601:surgery; D005500:Follow-Up Studies; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009336:Necrosis / Q000150:complications