Femorotibial Cartilage Thickness Change Distributions for Subjects without Signs, Symptoms, or Risk Factors of Knee Osteoarthritis

OBJECTIVE: To describe the distribution of longitudinal femorotibial cartilage thickness annualized rate of change (ΔThCtAB) from quasi–population-based studies, and to construct a reference distribution for men and women without signs, symptoms, or risk factors of knee osteoarthritis (OA). METHODS: Segmented baseline and 1-year follow-up MRI from 43 men and 69 women of the Osteoarthritis Initiative (OAI) asymptomatic control cohort without risk factors and also baseline and 2-year follow-up data from 77 asymptomatic women of the Pfizer A9001140 study were included. The mean, standard deviation (SD), and correlation of ΔThCtAB in medial and lateral femorotibial subregions were estimated; distributions were tested for normality and for differences between cohorts and gender. RESULTS: Distributions of femorotibial ΔThCtAB rates were consistent between cohorts and were normally distributed, with rates <0.7%/y. Subregion ΔThCtAB SDs were correlated with mean baseline cartilage thickness (ratio = 3%-5%). However, ΔThCtAB SD did not increase with baseline thickness when estimated for different tertiles of any given subregion, indicating the relationship may rather be due to spatial location than to baseline thickness. CONCLUSIONS: Distributions of (subregional) longitudinal cartilage thickness rates of change appear to be normally distributed, not significantly different from zero, and similar for different cohorts of asymptomatic subjects. Given the spatial heterogeneity of subregional cartilage change observed in OA knees, the proposed reference distribution of subregional, ΔThCtAB may be used to describe and identify structural progression (i.e., cartilage loss) in individual OA knees with greater accuracy and sensitivity than conventional approaches, such as minimal detectable difference.