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

Abstract

Objective: To establish sex-specific (subregional) reference values of cartilage thickness and potential maximal Z-scores in the femorotibial joint.

Methods: The 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).

Results: 686 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 (3.59 mm) than in the lateral femorotibial compartment (3.86 mm). Medially, the femur displayed thicker cartilage (1.86 mm) than the tibia (1.73 mm), and laterally the tibia thicker cartilage (2.09 mm) than the femur (1.77 mm). 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".

Conclusions: We 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.

Fig. 1

Schematic showing (A) View of the central (weight-bearing) femoral condyles (cMF/cLF) from inferior, (B) View of the central (weight-bearing) femoral condyles (cMF/cLF) and tibiae (MT/LT) from posterior, (C) View of the tibiae (MT/LT) from superior. Mean values and SDs of cartilage thickness (ThCtAB, averaged for men and women) from 686 normal subjects (KL grade 0) of the Framingham cohort are shown for femorotibial compartments, plates and subregions: MFTC = MT + cMF, LFTC = LT + cLF; subregion labels: c = central, e = external, i = internal, a = anterior, p = posterior.

Fig. 2

Bar graphs showing the mean and SD of cartilage thickness of the femorotibial cartilage plates in Framingham “normals” (no radiographic femorotibial OA), in Framingham “supernormals” (no radiographic femorotibial OA and no MRI features of cartilage lesions), and in non-exposed OAI reference cohort (no radiographic femorotibial OA, no symptoms of risk factors of knee OA) (A) Cartilage thickness in men (B) Cartilage thickness in women.

Fig. 3

Representative histograms of the cartilage thickness distribution in the MT and cMF from the Framingham cohort. (A) MT cartilage thickness distribution in men (B) MT cartilage thickness distribution in women (C) cMF cartilage thickness distribution in men (D) cMF cartilage thickness distribution in women.