Hamstring Activity and Lower Extremity Loading in Knee Osteoarthritis: The Effect of Foot Rotation
Lynn, Scott Kember
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Knee osteoarthritis (OA) causes more disability in community dwelling older adults than any other condition. The high costs associated with treating this disability suggest that research needs to focus on ways of preventing the development and progression of knee OA using low cost interventions such as exercise and modifications to certain activities of daily living. One such activity of daily living that has been implicated in the OA disease process is normal level walking or gait. Those with medial compartment knee OA are known to make certain modifications in their gait patterns in an attempt to unload the diseased compartment of their knee. Two of these modifications include the tendency of those with knee OA to walk with an externally rotated foot, and to increase the activity of their lateral hamstrings, while decreasing the activity of their medial hamstring during gait. Therefore, this work attempted to clarify this relationship between foot position, lower extremity loading and hamstring muscle activation patterns during both level walking and lower limb exercise. First, the changes in lower extremity loading with both internal and external rotation of the foot during gait were investigated in a group of young healthy subjects. It was discovered that internal rotation increased the magnitude of both the adduction moment and the medial-lateral shear force at the knee; while external rotation decreased both these measures. This suggests that external foot rotation may be an effective compensation strategy for those with medial knee OA and internal foot rotation may be an effective compensation strategy for those with lateral knee OA. Second, the same study was then repeated in a group of knee OA subjects and age matched healthy normal subjects; but in this work, hamstring EMG was also collected along with the external knee loads. Hamstring EMG data was used to calculate the medial-lateral (M-L) hamstring activation ratio. An increased M-L activation ratio would indicate an internal muscle moment tending to load the medial compartment more than the lateral; while a low M-L activation ratio would tend to unload the medial compartment. Those with knee OA had an increased late stance knee adduction moment and a decreased M-L hamstring activation ratio as compared to the healthy control group. Also, external foot rotation decreased the late stance knee adduction moment, lateral-medial shear force at the knee, and M-L hamstring activation ratio for both groups; but, internal foot rotation did not increase these measures. Lastly, since it is apparent that the hamstring may play a role in unloading the diseased knee compartment, the M-L activation ratio was calculated with changes in foot position during lower limb exercise in young healthy subjects to determine if selective activation of the medial or lateral hamstrings was indeed possible. It was discovered that internal foot rotation increases the M-L hamstring activation ratio and external rotation decreases it. Foot rotation has the ability to shift the external loads on the knee to one side of the joint or the other, and it also has the ability to alter internal knee loads created by hamstring muscular activation. Therefore, foot rotation during gait and lower limb exercise may be an effective intervention that could be used to delay the onset and progression of knee OA, keeping older adults active and healthy much longer.