title: Effect of alignment of the medial tibial plateau and x-ray beam on apparent progression of osteoarthritis in the standing anteroposterior knee radiograph.
abstract: OBJECTIVE
  Previous studies of knee osteoarthritis (OA) have yielded variable estimates of the rate of joint space narrowing (JSN) in the standing anteroposterior (AP) radiograph, due largely to longitudinal changes in the alignment of the medial tibial plateau (MTP) and x-ray beam. To characterize this bias, we examined serial radiographs of subjects with knee OA in population-based and clinical OA cohorts from 3 locations in the United States and the United Kingdom.
  
  
  METHODS
  Radiographic features of knee OA (e.g., osteophytosis, JSN) and MTP alignment in 428 OA knees were evaluated by consensus of 2 readers. Alignment was considered satisfactory if the anterior and posterior margins of the MTP were superimposed within 1 mm. Readers were blinded to subject identity, and films were read in random order. The minimum medial joint space width was also measured manually (standard error of repeated measurements 0.20 mm) in serial knee images.
  
  
  RESULTS
  Only 14% of serial radiographs exhibited alignment of the MTP in both images. In OA knees with satisfactory alignment in both images, the mean rate of JSN over 2-3 years (0.26 mm/year) was significantly larger (P = 0.004) than that in OA knees with misalignment in 1 or both radiographs and was 86% more rapid than the mean JSN in all OA knees. Moreover, the within-group standard deviation of JSN was significantly smaller among knees with reproduced alignment of the MTP than in knees in which misalignment occurred in 1 or both images (P = 0.006).
  
  
  CONCLUSIONS
  Poor standardization of knee positioning in serial standing AP radiographs in previous studies of OA progression has obscured the rate and variability of articular cartilage loss in subjects with knee OA. True JSN (i.e., JSN that is not attributable to longitudinal changes in the alignment of the MTP with the x-ray beam in serial radiographic examinations) may occur more rapidly, and with less between-subject variability, than that previously thought to be characteristic of knee OA.
authors.affiliation: Indiana University School of Medicine, Department of Medicine, Long Hospital, Indianapolis 46202-5100, USA.
authors.forename: S A
authors.initials: SA
authors.lastname: Mazzuca
authors.forename: K D
authors.initials: KD
authors.lastname: Brandt
authors.forename: P A
authors.initials: PA
authors.lastname: Dieppe
authors.forename: M
authors.initials: M
authors.lastname: Doherty
authors.forename: B P
authors.initials: BP
authors.lastname: Katz
authors.forename: K A
authors.initials: KA
authors.lastname: Lane
mesh_terms: D000368:Aged; D015331:Cohort Studies; D003951:Diagnostic Errors; D018450:Disease Progression; D005260:Female; D006801:Humans; D008297:Male; D008592:Menisci, Tibial / Q000000981:diagnostic imaging*; D020370:Osteoarthritis, Knee / Q000000981:diagnostic imaging* / Q000473:pathology; D011859:Radiography / Q000379:methods*