To evaluate the effect of medial tibial plateau (MTP) alignment of serial radiographs on the capacity to detect associations between baseline characteristics and progression of joint space narrowing (JSN) in knee osteoarthritis (OA).
Standardised posteroanterior weight-bearing knee radiographs of 83 knee OA patients were obtained at baseline and after 24 months using the non-fluoroscopic fixed-flexion protocol. Minimum joint space width (JSW) of the medial tibiofemoral joint spaces was measured manually in paired radiographs. Progression of JSN was defined by a change in JSW larger than the smallest detectable difference (0.4mm). Satisfactory MTP alignment was present if the distance between the anterior and posterior margins of the MTP was < or = 1mm. Standardised questionnaires were used to record age, sex and body mass index. Medial tibiofemoral JSN and osteophyte severity at baseline were graded with the Osteoarthritis Research Society International (OARSI) atlas.
Progression of JSN was observed in 31 (28.4%) of 109 OA knees. In the sub sample of 48 (44%) OA knees with satisfactory MTP alignment on baseline and 24-month radiographs, 18 (37.5%) knees progressed. Stronger (statistically significant) associations were found between sex, generalised OA, JSN and osteophyte severity at baseline and progression of JSN in the sub sample of radiographs with serial satisfactorily MTP alignment than in all radiographs together.
Insufficient quality of MTP alignment on serial radiographs could prevent detection of associations between baseline characteristics and progression of JSN in knee OA. These findings may have implications for longitudinal knee OA studies using the fixed-flexion protocol.