EVALUATING CARTILAGE HEALTH USING MULTIPLE IMAGING MODALITIES IN INDIVIDUALS WITH KNEE OSTEOARTHRITIS

Context: Knee osteoarthritis (OA) has been characterized as a “disease of mechanics,” whereby alterations in cartilage health interact with alterations in biomechanics to elicit potentially harmful changes within the joint that lead to the progression of knee OA. Previously established imaging modalities, such as MRI, are able to detect changes within the cartilage that are indicative of knee OA progression. However, imaging modalities such as MRI are costly, have long acquisition times, and are difficult to assess in conjunction with movement assessments to evaluate the interaction between these outcomes and biomechanical variables. Ultrasound (US) may serve as a feasible alternative to MRI, due to low-cost, portability, and short acquisition time. However, the feasibility of US in evaluating cartilage health in individuals with knee OA, compared to healthy individuals, remains unknown. Additionally, there is a dearth of knowledge surrounding the association between US outcomes of cartilage with previously established imaging modalities, as well as walking biomechanics. Objective: To determine the differences in US outcomes of femoral cartilage prior to and following a 3,000-step treadmill walking protocol in individuals with knee OA, compared to healthy controls. Additionally, this dissertation sought to determine the associations of US outcomes of femoral cartilage with T1rho MRI relaxation times, as well as walking biomechanics, in individuals with knee OA. Methodology: Cross-sectional area (CSA) and echo-intensity (EI) measures of femoral cartilage of the involved limb were assessed prior to and following a 3,000-step treadmill walking protocol. Additionally, percent change scores were calculated for CSA and EI to determine the magnitude of change that occurred due to the treadmill walking protocol. All US outcomes were collected in a group of young, healthy individuals who were included as a control group. Habitual walking speed was calculated using infrared timing gates and used for the treadmill walking protocol and walking biomechanics assessment. Overground walking biomechanics were collected for the involved limb during a single laboratory session while participants were wearing shoes. T1rho MRI relaxation times of the femoral cartilage of the involved limb were also collected. Statistical Analysis: A one-way analysis of variance was used to determine differences in resting and percent change US outcomes between individuals with knee OA and young healthy controls. These comparisons were subsequently repeated after accounting for covariates. Reliability, precision, and minimal detectable change values were calculated for individuals with knee OA. Separate linear regressions were conducted to determine the unique change in R2 (∆R2) between T1rho MRI relaxation times and US outcomes after accounting for covariates. Additionally, similar linear regressions were conducted to determine unique change in R2 (∆R2) between US outcomes and walking biomechanics and accounting for covariates. Results: Individuals with knee OA demonstrated significantly higher resting EI compared to healthy controls. Greater deformation (more negative percent change) in total and medial CSA following the treadmill walking protocol significantly associated with higher T1rho MRI relaxation times in individuals with knee OA. Further, greater peak knee flexion angle during walking significantly associated with greater resting EI for the total and medial region of femoral cartilage in individuals with knee OA. Conclusions: The results of this dissertation project suggest that US can detect differences in EI measures between individuals with knee OA and young healthy controls. Additionally, US outcomes significantly associate with a previously established imaging modality (T1rho MRI), as well as walking biomechanics, in individuals with knee OA. The feasibility of US as an alternative imaging modality, along with the results of the current study, suggest that further research with larger sample sizes is needed to determine whether US may provide clinicians with an alternative imaging modality for assessing cartilage health in individuals with knee OA.Doctor of Philosoph