Abstract
BackgroundChange in knee cartilage volume is frequently used as a proxy for change in knee joint space width over time, but longitudinal data on these associations is limited. We aimed to determine whether change in knee cartilage volume, new or worsening meniscal extrusion (ME), meniscal tears and cartilage defects over 2.4 years correlated with change in joint space width (JSW) over 5 years in older community dwelling adults.MethodsParticipants (n = 153) had their right knee imaged using MR imaging and x-ray at baseline, and after 2.4 years (MRI) and 5 years (x-ray). Cartilage volume, cartilage defects, meniscal extrusions and meniscal tears were assessed on sagittal T1-weighted fat-suppressed MRI. JSW was assessed using standard fixed semi-flexed view radiographs, and scored on those with adequate alignment.ResultsParticipants were 51–79 (mean 62) years old; 48 % were female. Cartilage volume reduced over time (medial −134 ± 202 μL/year, lateral −106 ± 165 μL/year, p < 0.001), as did JSW (medial −0.05 ± 0.16 mm/year, lateral −0.12 ± 0.24 mm/year, p < 0.001). In multivariable analysis, the only consistent predictor of change in JSW was new or worsening ME (medial tibia R2 3.1 %, p = 0.031; medial femur R2 3.2 %, p = 0.024); change in cartilage volume correlated with change in JSW laterally (R2 4.8 %, p = 0.007) and was borderline medially (R2 2.2 %, p = 0.064); there was no association for meniscal tears or cartilage defects. The magnitude of these associations were similar albeit somewhat greater for ME in participants with radiographic OA (R2 6.2 %, p = 0.017).ConclusionChange in ME and cartilage volume weakly predict change in JSW, but the vast majority of the variation remains unexplained. Since MRI examines cartilage directly while radiographs examine it indirectly, these results cast doubt on the validity of using JSW as a proxy measure of cartilage loss.
Highlights
Change in knee cartilage volume is frequently used as a proxy for change in knee joint space width over time, but longitudinal data on these associations is limited
Bold text indicates statistically significant result (p ≤ 0.05) R2 for univariable models is the proportion of variance explained provided (R2) for the linear regression R2 for multivariable models is the proportion of variance explained for individual components of the multivariable model Total R2 is the proportion of variance explained for the entire multivariable model effect did not reach statistical significance in any groups or sites, and the magnitude of the effect was less than meniscal extrusion
Bold text indicates statistically significant result (p ≤ 0.05) (No associations were statistically significant) R2 for univariable models is the proportion of variance explained provided (R2) for the linear regression R2 for multivariable models is the proportion of variance explained for individual components of the multivariable model Total R2 is the proportion of variance explained for the entire multivariable model whether cartilage loss using magnetic resonance imaging (MRI) should be adopted, as is being proposed by others [38, 39]
Summary
Change in knee cartilage volume is frequently used as a proxy for change in knee joint space width over time, but longitudinal data on these associations is limited. Change in joint space width (JSW) at the tibiofemoral joint has historically been considered a good measure of change in cartilage volume It is currently the gold standard for assessing osteoarthritis. Two studies reported weak but statistically significant correlation between changes in JSW and cartilage volume at 1 year in OA cohorts, using the fixed-flexion radiographic techniques [17, 20]. Hunter et al [23] assessed predictive value of cartilage score on change in medial JSN in patients with symptomatic knee OA over 30 months, using fluoroscopic positioning and fixed flexion They found that cartilage score contributed to change in JSN beyond age sex and BMI, but that most of the variability in JSN remained unexplained [23]. Since MRI has been directly validated for cartilage volume measurement, this raises the possibility that JSW is not a sufficiently adequate measure of cartilage to qualify it for use as an outcome measure in clinical trials
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