Diurnal variations in articular cartilage thickness and strain in the human knee

Abstract

Due to the biphasic viscoelastic nature of cartilage, joint loading may result in deformations that require times on the order of hours to fully recover. Thus, cartilaginous tissues may exhibit cumulative strain over the course of each day. The goal of this study was to assess the magnitude and spatial distribution of strain in the articular cartilage of the knee with daily activity. Magnetic resonance (MR) images of 10 asymptomatic subjects (six males and four females) with mean age of 29 years were obtained at 8:00 AM and 4:00 PM on the same day using a 3T magnet. These images were used to create 3D models of the femur, tibia, and patella from which cartilage thickness distributions were quantified. Cartilage thickness generally decreased from AM to PM in all areas except the patellofemoral groove and was associated with significant compressive strains in the medial condyle and tibial plateau. From AM to PM, cartilage of the medial tibial plateau exhibited a compressive strain of -5.1±1.0% (mean±SEM) averaged over all locations, while strains in the lateral plateau were slightly lower (-3.1±0.6%). Femoral cartilage showed an average strain of -1.9±0.6%. The findings of this study show that human knee cartilage undergoes diurnal changes in strain that vary with site in the joint. Since abnormal joint loading can be detrimental to cartilage homeostasis, these data provide a baseline for future studies investigating the effects of altered biomechanics on diurnal cartilage strains and cartilage physiology.

Figure 1

A sagittal view of an asymptomatic right human knee using a 3T MRI scanner. The cartilaginous and osseous boundaries of the femur (F), tibia (T), and patella (P) were segmented on each slice and stacked to create 3D models of the joint.

Figure 2

3D models of the right tibia (A), patella (B), and femur (C) showing grid scheme for computing thickness changes and strains. The patella is shown from a posterior view. Right femur is shown from an inferior view (left) and a posterior view (right).

Figure 3

Cartilage thickness maps of the tibia (A), femur (B), and patella (C) measured in the AM (left) and PM (right). (M = Medial, L=Lateral, A=Anterior, P=Posterior)

Figure 4

Mean (± sem) AM cartilage thickness varies significantly between compartments and with sex (ANOVA, location p<0.0001, sex p<0.0001, location*sex p=0.80). Symbols show significant differences from post-hoc tests for each factor (sex, location) (LSD post-hoc test with Bonferroni correction, p<0.025).

Figure 5

Mean (± sem) cartilage thickness decreases from AM to PM in most major knee compartments. *AM thickness significantly different from PM (paired t-test with Bonferroni correction, p<0.025).

Figure 6

Cartilage in most knee compartments undergoes significant diurnal compressive strain. Bars are mean (± sem). *strains significantly different from zero (t-test with Bonferroni correction, p<0.025). Bars with different letters are significantly different from one another (ANOVA, LSD post-hoc test with Bonferroni correction, p<0.025).