Browsing by Author "Henderson, Christopher"
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Item Effect of common gait modifications on knee joint loading and loading environment in persons with knee osteoarthritis(University of Delaware, 2015) Henderson, ChristopherKnee osteoarthritis (OA) is a leading cause of disability in older Americans affecting 12 percent of people greater than 60 years of age with these persons primarily complaining of knee pain and instability. Eighty percent of persons with painful OA report a limitation in functional mobility including 25 percent reporting they cannot perform a major activity of daily living (ADL). Walking is an important ADL frequently limited in this population and as such is frequently investigated with changes in preferred walking speed and knee kinematics being identified. The effectiveness, or lack thereof, of these gait modifications on joint loading is not currently well understood and was investigated in this dissertation. In Aim 1, we examined the effect of walking speed on cumulative joint loading after accounting for the distance traveled within the gait cycle and found that the reduced walking speed frequently exhibited by persons with knee OA is likely not an effective strategy to reduce cumulative joint loading. Furthermore, if these subjects were to increase their self-selected walking speeds to match that of their healthy older adult counterparts, a 2.7-10.4% reduction in cumulative joint loading would be possible. In Aim 2, we investigated the effect of the altered sagittal knee kinematics on the peak joint contact force (JCF) and identified that the reduced late stance knee extension exhibited by persons with knee OA was associated with a decrease in 2 nd peak JCF; however the increased early stance knee flexion exhibited by these subjects was associated with an increase in the 1st peak JCF. The 2nd peak JCF was found to be of significantly greater magnitude than the 1st peak, suggesting the altered sagittal knee kinematics observed by the population may be an effective strategy to reduce the magnitude of joint loading during gait. In addition to the duration and magnitude of joint loading, the area of loading distribution significantly influences the contact stresses experienced within the joint. The articular cartilage contact area has previously been found to be a valid surrogate for the area of loading distribution and we identified that accounting for the anthropometric variation in this measure before evaluating changes with the development of OA is an important consideration (Aim 3). Kinematic (Aim 4a) and kinetic changes (Aims 4b,c) that resulted in an increase in joint loading were associated with a corresponding increase in the area of loading distribution in healthy older adults, but not in subjects with knee OA suggesting that in addition to the elevated joint loading frequently observed in this population, the joint loading environment may also be altered. The results of these studies should be used as the basis for longitudinal studies to identify those at risk of developing knee OA and those with established OA with the long term goal of developing rehabilitation strategies to minimize the effect of the disease on ADLs.Item Use of a novel magnetic resonance imaging based modeling technique to investigate differences in tibiofemoral articular cartilage contact area In subjects with moderate knee osteoarthritis(University of Delaware, 2009) Henderson, ChristopherKnee osteoarthritis (OA) detrimentally impacts the lives of millions of older Americans through pain and decreased functional ability. Unfortunately, the pathomechanics and associated changes that OA patients experience are not well understood. Mechanical stress in the knee joint may play an essential role in OA; however existing literature in this area is limited. Purpose: The purpose of this study was two-fold. First, we wanted to evaluate an existing magnetic resonance imaging (MRI) based modeling method’s estimation of articular cartilage contact area in vivo. Secondly, we wanted to apply this method to a cohort of subjects with moderate knee OA and compare their medial compartment articular cartilage contact area estimates with healthy, age matched controls. Methods: In order to establish confidence in the modeling method’s ability to estimate articular cartilage contact area, imaging data on a single, healthy subject were collected and compared to existing contact area estimates in the literature. Intra-observer reliability and sensitivity studies were also performed in an attempt to further establish confidence in the method. In the second half of this study, MRIs of the knee at 0°, 15°, and 30° flexion were collected during partial-weightbearing in subjects with moderate knee OA (n = 11) and healthy, age matched controls (n = 11). Articular cartilage contact area estimates were normalized to an approximation of the surface area of the tibial plateau in order to account for joint size differences between subjects. The relationship between medial compartment articular cartilage contact area and knee flexion was investigated in each group. Results: The single healthy subject was found to have articular cartilage contact areaestimates similar to those reported in the literature. The method was found to be sensitive to changes in the cartilage tracings on the peripheries of the compartment and demonstrated an intra-observer reliability of 0.95 when assessed using Pearson’s correlation coefficient. In the second half of the study, medial compartment articular cartilage contact area in the healthy controls was found to be significantly correlated with knee flexion angle (p ≤ 0.01), while no such correlation was found in the moderate OA subjects (p = 0.34). Linear regression analysis found that the moderate knee OA subjects had higher articular cartilage contact areas than their healthy, control counterparts across all flexion angles considered. Conclusions: Confidence was established in the MRI based knee modeling method’s ability to estimate articular cartilage contact area through a series of assessments and comparison with existing literature on healthy subjects. Healthy subjects were found to have a significant correlation between medial compartment articular cartilage contact area and knee flexion, which agreed with the literature. The moderate OA subjects did not show the same relationship between medial compartment articular cartilage contact area and knee flexion. Regression analysis found that they had higher medial compartment articular cartilage contact area estimates in all instances when compared with healthy controls. Increased contact area may be a biomechanical adaptation in response to OA in order to decrease the mechanical stress applied across the painful joint.