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 ten asymptomatic subjects (six males, four females) with mean age of 29 years were obtained at 8:00AM and 4:00PM 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.

Introduction Altered local mechanical loading may disrupt normal cartilage homeostasis and play a role in the progression of osteoarthritis. Currently, there is limited data quantifying local cartilage strains in response to dynamic activity in normal or injured knees. Purpose The purpose of this study was to directly measure local tibiofemoral cartilage strains in response to a dynamic hopping activity in normal healthy knees. We hypothesize that local regions of cartilage will exhibit significant compressive strains in response to hopping, while overall compartmental averages may not. Study Design Controlled laboratory study. Methods Both knees of eight healthy subjects were MR imaged before and immediately after a dynamic hopping activity. Images were segmented and then used to create 3D surface models of bone and cartilage. These pre- and post-activity models were then registered using an iterative closest point technique to enable site-specific measurements of cartilage strain (defined as the normalized change in cartilage thickness before and after activity) on the femur and tibia. Results Significant strains were observed in both the medial and lateral tibial cartilage, with each compartment averaging a decrease of 5%. However, these strains varied with location within each compartment, reaching a maximum compressive strain of 8% on the medial plateau and 7% on the lateral plateau. No significant averaged compartmental strains were observed in the medial or lateral femoral cartilage. However, local regions of the medial and lateral femoral cartilage experienced significant compressive strains, reaching maximums of 6% and 3% respectively. Conclusion Local regions of both the femur and tibia experienced significant cartilage strains as a result of dynamic activity. An understanding of changes in cartilage strain distributions may help to elucidate the biomechanical factors contributing to cartilage degeneration after joint injury.

Objective Obesity is an important risk factor for osteoarthritis and is associated with changes in both the biomechanical and inflammatory environments within the joint. However, the relationship between obesity and cartilage deformation is not fully understood. The goal of this study was to determine the effects of body mass index (BMI) on the magnitude of diurnal cartilage strain in the knee. Methods Three-dimensional maps of knee cartilage thickness were developed from 3T magnetic resonance images of asymptomatic age- and sex-matched subjects with normal (18.5–24.9 kg/m2) or high (25–31 kg/m2) BMI. Site-specific magnitudes of diurnal cartilage strain were determined using aligned images recorded at 8:00 AM and 4:00 PM on the same day. Results High BMI individuals had significantly thicker cartilage on the patella and femoral groove than the normal BMI individuals. Diurnal cartilage strains were dependent on location as well as BMI. Subjects with high BMI exhibited significantly higher compressive strain in tibial cartilage than did those with normal BMI. Cartilage thickness decreased significantly on both femoral condyles from the AM to PM time point; however, there was no significant effect of BMI on diurnal cartilage strain in the femur. Conclusions Increased BMI is associated with increased diurnal strains in the articular cartilage of both the medial and lateral compartments of the knee. The increased cartilage strains measured in high BMI individuals may, in part, explain the elevated OA risk associated with obesity or may reflect altered cartilage mechanical properties in subjects with high BMI.

Altered joint motion has been thought to be a contributing factor in the long-term development of osteoarthritis after ACL reconstruction. While many studies have quantified knee kinematics after ACL injury and reconstruction, there is limited in vivo data characterizing the effects of altered knee motion on cartilage thickness distributions. Thus, the objective of this study was to compare cartilage thickness distributions in two groups of patients with ACL reconstruction: one group in which subjects received a non-anatomic reconstruction that resulted in abnormal joint motion and another group in which subjects received an anatomically placed graft that more closely restored normal knee motion. Ten patients with anatomic graft placement (mean follow-up: 20 months) and 12 patients with non-anatomic graft placement (mean follow-up: 18 months) were scanned using high-resolution MR imaging. These images were used to generate 3D mesh models of both knees of each patient. The operative and contralateral knee models were registered to each other and a grid sampling system was used to make site-specific comparisons of cartilage thickness. Patients in the non-anatomic graft placement group demonstrated a significant decrease in cartilage thickness along the medial intercondylar notch in the operative knee relative to the intact knee (8%). In the anatomic graft placement group, no significant changes were observed. These findings suggest that restoring normal knee motion after ACL injury may help to slow the progression of degeneration. Therefore, graft placement may have important implications on the development of osteoarthritis after ACL reconstruction.