Osteoarthritis is a painful degenerative joint disease affecting millions of people in the U.S. The pathogenesis of articular cartilage disease is characterized bysoftening of cartilage and loss and disruption of constituent macromolecules including proteoglycans and collagen. In current orthopaedic surgical practice, the gold standard for evaluating articular cartilage integrity is the use of a hand probe during arthroscopy. Mechanical probing, however, is invasive and requires anesthesia. Tightly confined areas of the articular surface can be difficult to reach and assess, and manual probing provides a subjective rather than a quantitative assessment of cartilage mechanical integrity.

This thesis was motivated by the desire for a noninvasive and nondestructive means to map the variation in mechanical stiffness of an articular surface. Such a method could potentially have application to guiding surgeons during procedures and quantitatively assessing the efficacy of medical and surgical therapies. It could also potentially provide patient-specific, in vivo tissue mechanical property data for surgical simulation and preoperative procedure planning.

The macromolecule glycosaminoglycan (GAG) is a significant determinant of cartilage stiffness. GAG content can be assessed noninvasively in vivo and in vitro by an MRI-based technique known as delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC), which measures the MRI parameter TI after equilibration with the ionic contrast agent Gd(DTPA)². With dGEMRIC, TGd serves as an index of GAG content:​ we thereforexamined whether cartilage stiffness could be related to dGEMRIC-measured T1_Gd in samples of human tibial plateaus.

We developed an experimental methodology to permit indentation test sites and regions in dGEMRIC scans to be registered with submillimeter accuracy. We found that the load response to focal indentation (a measure of local stiffness) and locally-averaged T1_Gd were in general highly correlated (Pearson correlation coefficients r = .80, .90, .64, .81 (p < .002) for four different patient samples, 130 total test locations). We further demonstrated that the observed correlation is not a simple consequence ofcartilage thickness effects. We observed that the parameters ofthe stiffness-T1_Gd relationship differed in some samples between the region of the tibial plateau covered by the meniscus in vivo and the more central region normally in contact with the femoral condyle. This suggests that another factor such as surface architecture orcollagen integrity also influences the indentation response of the articular surface