Reference values and Z-scores for subregional femorotibial cartilage thickness – results from a large population-based sample (Framingham) and comparison with the non-exposed Osteoarthritis Initiative reference cohort

SummaryObjectiveTo establish sex-specific (subregional) reference values of cartilage thickness and potential maximal Z-scores in the femorotibial joint.MethodsThe mean cartilage thickness (ThCtAB.Me) in femorotibial compartments, plates and subregions was determined on coronal magnetic resonance imaging (MRI) from a population-based sample (Framingham) and from a healthy reference sample of the Osteoarthritis Initiative (OAI).Results686 Framingham participants (309 men, 377 women, age 62±8 years) had no radiographic femorotibial osteoarthritis (OA) (“normals”) and 376 (156 men, 220 women) additionally had no MRI features of cartilage lesions (“supernormals”). The Framingham “normals” had thinner cartilage in the medial (3.59mm) than in the lateral femorotibial compartment (3.86mm). Medially, the femur displayed thicker cartilage (1.86mm) than the tibia (1.73mm), and laterally the tibia thicker cartilage (2.09mm) than the femur (1.77mm). The thickest cartilage was observed in central, and the thinnest in external femorotibial subregions. Potential maximal Z-scores ranged from 5.6 to 9.8 throughout the subregions; men displayed thicker cartilage but similar potential maximal Z-scores as women. Mean values and potential maximal Z-scores in Framingham “supernormals” and non-exposed OAI reference participants (112 participants without symptoms or risk factors of knee OA) were similar to Framingham “normals”.ConclusionsWe provide reference values and potential maximal Z-scores of cartilage thickness in middle aged to elderly non-diseased populations without radiographic OA. Results were similar for “supernormal” participants without MRI features of cartilage lesions, and in a cohort without OA symptoms or risk factors. A cartilage thickness loss of around 27% is required for attaining a Z-score of −2