title: Association of facet tropism and progressive facet arthrosis after lumbar total disc replacement using ProDisc-L.
abstract: OBJECTIVE
  The purpose of this retrospective study was to examine the association of facet tropism and progressive facet arthrosis (PFA) after lumbar total disc replacement (TDR) surgery using ProDisc-L.
  
  
  METHODS
  A total of 51 segments of 42 patients who had undergone lumbar TDR using ProDisc-L between October 2003 and July 2007 and completed minimum 36-month follow-up period were retrospectively reviewed. The changes of facet arthrosis were categorized as non-PFA and PFA group. Comparison between non-PFA and PFA group was made according to age, sex, mean follow-up duration, grade of preoperative facet arthrosis, coronal and sagittal prosthetic position and degree of facet tropism. Multiple logistic regression analysis was also performed to analyze the effect of facet tropism on the progression of facet arthrosis.
  
  
  RESULTS
  The mean age at the surgery was 44.43 ± 11.09 years and there were 16 males and 26 females. The mean follow-up period was 53.18 ± 15.79 months. Non-PFA group was composed of 19 levels and PFA group was composed of 32 levels. Age at surgery, sex proportion, mean follow-up period, level of implant, grade of preoperative facet arthrosis and coronal and sagittal prosthetic position were not significantly different between two groups (p = 0.264, 0.433, 0.527, 0.232, 0.926, 0.849 and 0.369, respectively). However, PFA group showed significantly higher degree of facet tropism (7.37 ± 6.46°) than that of non-PFA group (3.51 ± 3.53°) and p value was 0.008. After adjustment for age, sex and coronal and sagittal prosthetic position, multiple logistic regression analysis revealed that facet tropism of more than 5° was the only significant independent predictor of progression of facet arthrosis (odds ratio 5.39, 95 % confidence interval 1.251-19.343, p = 0.023).
  
  
  CONCLUSIONS
  The data demonstrate that significant higher degree of facet tropism was seen in PFA group compared with non-PFA group and facet tropism of more than 5° had a significant association with PFA after TDR using ProDisc-L.
authors.affiliation: Department of Neurosurgery, Seoul St. Mary's Hospital, The Catholic University, 505 Banpo-Dong, Seocho-Ku, Seoul 137-701, South Korea.
authors.forename: Myung-Hoon
authors.initials: MH
authors.lastname: Shin
authors.forename: Kyeong-Sik
authors.initials: KS
authors.lastname: Ryu
authors.forename: Jung-Woo
authors.initials: JW
authors.lastname: Hur
authors.forename: Jin-Sung
authors.initials: JS
authors.lastname: Kim
authors.forename: Chun-Kun
authors.initials: CK
authors.lastname: Park
mesh_terms: D000328:Adult; D000368:Aged; D018450:Disease Progression; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000601:surgery*; D007592:Joint Diseases / Q000000981:diagnostic imaging / Q000453:epidemiology / Q000209:etiology*; D008159:Lumbar Vertebrae / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D019736:Prostheses and Implants / Q000009:adverse effects; D012044:Regression Analysis; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D059145:Total Disc Replacement / Q000009:adverse effects*; D021801:Zygapophyseal Joint / Q000000981:diagnostic imaging*