Comparison of the internal hip abduction moment and the pelvic kinematics during single-leg standing between people with knee osteoarthritis and healthy elderly people

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Purpose: A high external knee adduction moment (KAM) during walking is known as the risk factors for progression of knee osteoarthritis (KOA). Recent studies demonstrated that contralateral pelvic drop increased the KAM during walking and single-leg standing. Thus, stabilizing pelvis in the frontal plane is one of the goal for conservative treatments for KOA. In addition, internal hip abduction moment (HAM) explaining hip abductor muscle strength of the stance limb play a role in stabilizing the pelvis. However, few studies investigated HAM and pelvic kinematics during single-leg standing in people with KOA. Single-leg standing is convenient method to assess movement of the pelvis in the frontal plane, such as in the Trendelenburg test. The purpose of the present study was to compare the HAM and the pelvic kinematics during single-leg standing between people with KOA and healthy elderly people. Methods: Nine healthy elderly people (healthy group; age: 61.0 ± 9.0 years, height: 157.0 ± 9.3 cm, weight: 57.3 ± 11.2 kg) and 10 patients with KOA (KOA group; age: 67.8±8.9 years, height:152.8±6.9 cm, weight: 56.8±15.1 kg, K/L grade: 2-3) were recruited for this study. These subjects performed the single-leg standing trials. Subjects stood on two force platforms. They lifted one lower limb off the force plate 'as fast as possible' following a sonic cue, and held the posture. The onset of lift-off point was defined as the time when the vertical component of the ground reaction force became less than 10 N. All data were recorded until 3000ms following the lift-off. The data were collected with a six-camera motion analysis system and two force plates that were temporally synchronized and sampled at 200Hz and 1000Hz, respectively. Helen Hays marker set was used. The peak HAM and peak KAM during the single-leg standing were determined using the SIMM6.0.2 software. The maximum and minimum value of the lateral tilt angle of the pelvis during single-leg standing trials were calculated using the custom Matlab code. The contralateral pelvic elevation was denoted as a positive angle. We compared peak HAM, peak KAM and pelvic tilt angle between groups using unpaired t test. The level of significance was set at 0.05. Results: able 1 shows all kinematics and kinetic data (mean and SD) and statistics. There was no significant difference between groups for peak HAM and peak KAM. Maximum value of the pelvic tilt angle was not significant difference between groups. Minimum value of the pelvic tilt angle was greater in KOA group than in healthy group (p<0.05). Conclusions: People with KOA reduced the contralateral pelvic drop during single-leg standing. In addition, there was no difference peak KAM and peak HAM in KOA group compared with healthy group. People with KOA probably adapted their pelvic kinematics to prevent the increase of peak KAM during single-leg standing. Since hip abductor muscle play a role in stabilizing pelvis, hip abductor muscle strengthening exercises might be effective for rehabilitation program for KOA.