Response of knee cartilage T1rho and T2 relaxation times to in vivo mechanical loading in individuals with and without knee osteoarthritis

Objective: The objective of this study was to evaluate the effects of mechanical loading on knee articular cartilage T-1 rho and T-2 relaxation times in patients with and without osteoarthritis (OA). Design: Magnetic resonance (MR) images were acquired from 137 subjects with and without knee OA under two conditions: unloaded and loaded at 50% body weight. Three sequences were acquired: a high-resolution 3D-CUBE, a T-1 rho relaxation time, and a T-2 relaxation time sequences. Cartilage regions of interest included: medial and lateral femur (MF, LF); medial and lateral tibia (MT, LT), laminar analysis (superficial and deep layers), and subcompartments. Changes in relaxation times in response to loading were evaluated. Results: In response to loading, we observed significant reductions in T-1 rho relaxation times in the MT and LT. In both the MF and LF, loading resulted in significant decreases in the superficial layer and significant increases in the deep layer of the cartilage for T-1 rho and T-2. All subcompartments of the MT and LT showed significant reduction in T-1 rho relaxation times. Reductions were larger for subjects with OA (range: 13-19% change) when compared to healthy controls (range: 3-13% change). Conclusions: Loading of the cartilage resulted in significant changes in relaxation times in the femur and tibia, with novel findings regarding laminar and subcompartmental variations. In general, changes in relaxation times with loading were larger in the OA group suggesting that the collagen-proteoglycan matrix of subjects with OA is less capable of retaining water, and may reflect a reduced ability to dissipate loads. (C) 2014 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.