Relationship between cartilage stiffness and dGEMRIC index: correlation and prediction

Abstract

We sought to determine if a generalized relationship between the dGEMRIC index (T1Gd relaxation time) and compressive stiffness of articular cartilage could be defined across multiple samples. Osteochondral blocks were cut from 12 human tibial plateaus, six from cadaveric sources and six from total knee replacement surgeries. Each block contained submeniscal ("covered") and extrameniscal ("uncovered") cartilage regions. At approximately 18 sites per block, a pulse indentation was applied and local dGEMRIC index was determined using dGEMRIC MRI. No correlation was found between stiffness and full cartilage depth dGEMRIC index. When averaged over the depth comparable to the indentation, good correlations were found between stiffness and the dGEMRIC index whether all data were combined, or whether each sample/region was considered independently. However, the standard error of the estimate for predicting stiffness from the local dGEMRIC index was improved when the uncovered and covered regions were considered separately. Further improvement in predictive capacity was obtained if, rather than predict absolute stiffness, differences in the dGEMRIC index across a region were used to predict difference in stiffness. The dGEMRIC index is highly correlated to mechanical stiffness. A generalized relationship was found to provide good correspondence across sources and regions. Use of the dGEMRIC index as a predictive measure of stiffness is possible, depending on the application's acceptable error.