Childs, JD, Irrgang, JJ, Sparto, PJ, Fitzgerald, GK, and Bizzini, M; Department of Physical Therapy, School of Health and Rehabilitation Sciences, University of Pittsburgh, Pittsburgh, PA, USA. childsjd@bigfoot.com.

PURPOSE: Knee osteoarthritis (KOA) results in significant pain and disability. Individuals with KOA have been found to have altered movement and muscle activation patterns during level walking that are associated with decreased function. Individuals with KOA also report difficulty negotiating stairs. The purpose of this study was to determine if similar alterations in movement and muscle activation patterns exist during a step task in individuals with KOA compared to age- and gender matched controls. SUBJECTS: This study utilized a case-control design to compare 25 subjects with unilateral symptomatic KOA to 25 age- and gender-matched controls without KOA. The average age of the subjects was 61.7 ± 9.5 years. 56% were female. METHODS: A gait analysis was performed to determine the kinematics, kinetics, and muscle activity when descending from an 8-inch step. Knee and hip kinematics were measured using electromagnetic position/orientation sensors placed on the shank, thigh, and waist. Vertical ground reaction forces were measured using a 6-degree of freedom force platform. Timing and amplitude of muscle activation was monitored using surface electromyography (EMG) electrodes placed over the vastus lateralis, medial hamstrings, tibialis anterior and medial gastrocnemius. Muscle co-activation was assessed by comparing the normalized amplitude of antagonistic muscle pairs. ANALYSIS: Paired t-tests (1-tail) were used to compare the average of five trials between the involved side of the KOA subject and the same side of the matched control subject at an a priori alpha-level of .05. RESULTS:

CONCLUSIONS: One of the functions of the knee during gait is to flex to absorb shock. Decreased knee excursion combined with increased duration of muscle activity and trends toward increased muscle co-activation in individuals with KOA indicates that these individuals utilize a gait pattern when negotiating a step that may interfere with the knee's ability to dissipate loads, which may lead to progression of the disease. In order to improve function, rehabilitation strategies that increase knee excursion and decrease muscle co-activation patterns may need to be developed. FUNDING SOURCE: Orthopaedic Section and Foundation for Physical Therapy of the American Physical Therapy Association.

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