The effect of contralateral pelvic drop and trunk lean on frontal plane knee biomechanics during single limb standing.

Pelvic drop as a result of hip abductor weakness has been hypothesized as a potential modifier of frontal plane knee joint kinetics during gait in individuals with pathology such as knee osteoarthritis (OA). However, hip muscle strengthening interventions have failed to find significant reductions in frontal plane loading measures such as the external knee adduction moment (KAM) with altered hip strength. Since this could in part be due to a lack of change in pelvic kinematics between conditions or test sessions or due to alterations in lateral trunk lean angle, the relationship between pelvic drop and subsequent changes in centre of mass with knee joint loading remains unclear. The purpose of this study was to examine the effect of a consciously altered frontal plane centre of mass position (pelvic drop and trunk lean to the contralateral side) on the KAM during single limb standing. Twenty healthy individuals performed a series of single limb standing trials, where they were asked to balance on their dominant leg. KAM was assessed during single limb stance in two conditions: with pelvis and trunk maintained in a level position, and with contralateral pelvic drop. A third condition involving contralateral pelvic drop and trunk lean was assessed to examine exaggerated changes in centre of mass. The KAM increased significantly with contralateral pelvic drop (p=0.001) and with combined contralateral pelvic drop and trunk lean (p<0.001) compared to the level pelvis trials. These findings suggest that pelvic drop alone can significantly increase KAM magnitude, a risk factor for the progression of knee OA. Assessment of pelvic obliquity prior to treatment may allow those with marked pelvic drop to be targeted for hip muscle strengthening.