title: Can anatomic alignment measured from a knee radiograph substitute for mechanical alignment from full limb films?
abstract: OBJECTIVE
  To examine whether categories of anatomic alignment (varus, neutral, valgus) measured from knee X-rays agree with similar categories of mechanical alignment from the full limb film and whether varus anatomic malalignment predicts medial joint space loss on knee X-rays as well as varus mechanical alignment.
  
  
  METHODS
  We used data from the Osteoarthritis Initiative (OAI) (full limb and flexed knee X-rays) to examine agreement of anatomic and mechanical alignment and data from Boston Osteoarthritis of the Knee Study (BOKS) to evaluate the association of full limb mechanical alignment vs knee X-ray anatomic alignment with joint space loss. A 4 degree offset was used to correct for the more valgus angulation of the anatomic alignment.
  
  
  RESULTS
  Of 143 subjects whose knee X-rays and full limb films were publicly released from the OAI, the agreement of varus, neutral and valgus alignment was only moderate (kappa=0.43, P<0.001). In BOKS, varus mechanical and anatomic alignments measured from full limb and knee X-rays respectively both predicted a high risk of medial joint space loss vs neutral alignment--for mechanical alignment, odds ratio (OR)=4.82 [95% confidence interval (CI) 1.93, 12.00] and for anatomic alignment OR=4.25 (95% CI 2.08, 8.72).
  
  
  CONCLUSIONS
  While agreement of alignment from knee X-ray to full limb film was only moderate, varus malalignment measured from a flexed knee predicted the likelihood of progression well. Flexed knee alignment may be more relevant to knee osteoarthritis (OA) risk than that of a fully extended knee, but a measurement of alignment from a short limb is an imperfect surrogate for full limb alignment.
authors.affiliation: Clinical Epidemiology Unit, Boston University, Boston, MA 02118, USA. ncarras@bu.edu
authors.forename: D T
authors.initials: DT
authors.lastname: Felson
authors.forename: T D V
authors.initials: TD
authors.lastname: Cooke
authors.forename: J
authors.initials: J
authors.lastname: Niu
authors.forename: J
authors.initials: J
authors.lastname: Goggins
authors.forename: J
authors.initials: J
authors.lastname: Choi
authors.forename: J
authors.initials: J
authors.lastname: Yu
authors.forename: M C
authors.initials: MC
authors.lastname: Nevitt
mesh_terms: D000368:Aged; D017760:Bone Malalignment / Q000000981:diagnostic imaging*; D016001:Confidence Intervals; D018450:Disease Progression; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D008875:Middle Aged; D016017:Odds Ratio; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging*; D011237:Predictive Value of Tests; D011859:Radiography; D014965:X-Rays