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The effects of valgus bracing on the 3D kinematics of gait in patients with osteoarthritis of the knee Davidson, Peter Lawrence


Clinical evidence suggests that there can be a reduction of pain by wearing a valgus knee brace for treatment of unicompartmental medial osteoarthritis of the knee (Horlick and Loomer, 1991). It has been suggested that the brace alters the orientation of the thigh and shank segments during gait in such a manner as to reduce the inter-joint pressure of the afflicted compartment. This study was designed to test the hypothesis that the knee brace alters the alignment of the shank segment with respect to the thigh segment. As a part of this study twelve subjects was recruited. Each had been diagnosed with medial compartment osteoarthritis of one knee and for treatment, prescribed a valgus knee brace (Generation II Orthotics Unloader). Prior to the study, the subjects had worn the brace for over one month on a daily basis and report pain relief compared to the time before they received their brace. While walking on a treadmill at either of two speeds the each of the subjects was filmed by two gen-locked video cameras of 60 Hz. A total of five reflective markers were placed on the thigh and shank segments of the afflicted leg. After digitizing the marker points recorded by two cameras, the three dimensional coordinates were determined using the direct linear transformation method. From these data the movements and flexion, varus and axial rotation angles of the thigh and shank segments in a global coordinate system were determined. The data analyzed was the normalized average of five sequential step cycles where each cycle was the time from one heel-strike to the next heel-strike of the same foot of the afflicted leg. The values of the angles were calibrated with respect to the standing position,”no-brace” condition, i.e. those readings were taken to be the reference point for each subject. The study was a repeated measured design with two factors and 23 dependent variables. The factors of interest were brace condition: i.e., no-brace and brace, and walking speed: i.e., medium and fast. Thus, there were four conditions defined by combining the levels of the two factors. Each of the 12 subjects were tested at every condition. Therefore, the study was a (12:subject X 2:brace X 2:speed) RM design. The statistical analysis consisted of twenty three ANOVAs at the p<O.05 significance level. The hypotheses were that there there was no difference of the percent cycle timing during the stance phase and no difference of the flexion angle between the no-brace and brace conditions across all subjects at either walking speed. But it was expected that there will be a decrease in the coronal angle (i.e., towards valgus) and of the axial angle (i.e., internal rotation) of the thigh and shank and this difference will be greater at the fast speed compared to the medium speed, i.e., there is an interaction effect. All the hypotheses were tested at four specific points in time during the stance phase. The results showed that the brace did have a significant effect but not in the way anticipated. The brace had no effect on the thigh coronal angle but was significant in reducing the shank coronal angle into varus at toe-off The brace also prevented full extension during mid-stance but this was believed to be caused by resisting valgus forces in the coronal plane transmitted through the braces helical strap. This same strap is also believed to be responsible for axial forces that created the significant external rotation of the thigh axial angle throughout the stance phase and the external rotation of the shank axial angle during knee flexion. Dynamic forces of the brace hinge may explain the unexpected internal rotation of the shank axial angle that accompanied knee extension. There was a possibility that the subject interacted with the brace in a complex way to produce some of the observed motion.

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