Applied Assessment Method for Varus Thrust during Walking in Patients with Knee Osteoarthritis Using Acceleration Data Measured by an Inertial Measurement Unit

Abstract

We developed a novel quantitative method to assess varus thrust during walking using acceleration data obtained from an inertial measurement unit (IMU). This study aimed to examine the reliability of the developed index and to evaluate its ability to distinguish patients with knee osteoarthritis (OA) with varus thrust from healthy adults. Overall, 16 patients with knee OA and 16 healthy adults walked on a treadmill with IMUs attached to the tibial tuberosity and lateral femoral condyle. As an index of varus thrust, we used the root mean square (RMS) of acceleration in the mediolateral direction. This value was adjusted by dividing it by swing speed while walking (adjusted RMS, A-RMS) because the RMS of the acceleration was strongly coupled with the speed of motion. The intraclass correlation coefficients of A-RMS of the tibia and femur were 0.85 and 0.73, respectively. Significant differences were observed in the A-RMSs of the tibia and femur, with large effect sizes between the patients with knee OA and healthy adults (Cohen’s d: 1.23 and 0.97, respectively). Our results indicate that A-RMS has good test–retest reproducibility and can differentiate patients with varus thrust from healthy adults.

Association of the Degree of Varus Thrust during Gait Assessed by an Inertial Measurement Unit with Patient-Reported Outcome Measures in Knee Osteoarthritis

“…A higher VT-index value means a greater degree of VT. The reliability and validity of this index for Japanese populations were confirmed before by the authors [ 38 ].…”

“…The mean VT-index was 0.036 ± 0.012 m/s/deg (range, 0.016–0.064 m/s/deg). Most subjects (n = 53, 75.7%) exceeded the cutoff value (0.027 m/s/deg) of VT from previous studies [ 38 ].…”

“…The protocol to assess the degree of VT was the same as that previously reported [ 38 ]. Briefly, the patients walked on a treadmill at a comfortable speed with an IMU attached to the tibia on the affected side.…”

“…For the index of VT during walking (VT-index), the adjusted root mean square (RMS) of the acceleration at the tibia in the ML direction was calculated. The typical signals of acceleration from the IMU and the calculation method have been described elsewhere [ 38 ]. In brief, the VT-index was calculated by dividing the RMS of the acceleration data of the first halves of the stance phase in the ML direction by the mean of the RMS of the angular velocity data of the swing phase in the three planes because the RMS of the acceleration was considered strongly coupled with the swing speed of the lower extremity.…”

“…As an objective and quantitative method for assessing the degree of VT, the method using inertial measurement units (IMU) has been reported recently [ 34 , 35 , 36 , 37 , 38 ]. A report demonstrated that the index of VT calculated from acceleration and angular velocity data from an IMU attached to the tibia has good test–retest reliability and good discriminative ability for VT [ 38 ]. IMUs are increasingly being used in various clinical settings because of their convenience compared with motion analysis systems [ 39 , 40 ].…”