To test the hypothesis that cartilage displays significant longitudinal thickening in the external subregions of the central medial femur (ecMF) and lateral femur (ecLF) in knees with early radiographic osteoarthritis (ROA) compared with contralateral knees without ROA, and to explore differences in change in other subregions and in radiographic joint space width (JSW).
Fifty participants (50% women, mean ± SD age 61.1 ± 9.7 years, and mean ± SD body mass index 27.7 ± 4.7 kg/m2) were identified from the Osteoarthritis Initiative cohort with definite femorotibial osteophytes but no joint space narrowing (JSN) in 1 knee (early ROA), and no osteophytes or JSN in the contralateral knee (non-ROA). A longitudinal within-person, between-knee comparison was performed using measures of subregional cartilage thickness based on analyses of sagittal double-echo steady-state magnetic resonance images obtained at baseline and 1 year. Medial JSW was evaluated from fixed-flexion radiographs.
The change between baseline and 1 year was −6 ± 94 μm in ecMF and +18 ± 91 μm in ecLF in early ROA (P = 0.78) versus −1 ± 68 μm and +4 ± 76 μm in non-ROA knees (P = 0.38). The variability of cartilage thickness change tended to be greater in early ROA than in non-ROA knees. Greater cartilage thickness loss in the lateral tibia and a greater reduction in minimum medial JSW were observed in early ROA versus non-ROA knees.
There was no direct evidence of longitudinal cartilage thickening in external subregions of the central femur in knees with early ROA compared with contralateral non-ROA knees. The observed greater variability in longitudinal thickness change in early ROA knees (but not in non-ROA knees) might be due to cartilage thickening and thinning occurring simultaneously in these knees.