Diagnostic Accuracy of the Mobile Assessment of Varus Thrust Using Nine-axis Inertial Measurement Units

Abstract

Objectives: The purpose of this study was to clarify the diagnostic accuracy of the mobile assessment of varus thrust using inertial measurement units (IMUs). Methods: A total of 80 knees in 49 patients were enrolled in this study. On visual analysis of gait to determine the presence or absence of varus thrust, 23 knees were assigned to the Present group, 17 to the Ambiguous group, and 40 to the Absent group. The peak knee varus angular velocities (PVVs), measured by quantitative gait analysis using nine-axis IMUs, were compared between these three groups. A receiver operating characteristic curve for the relationship between the visual assessment of varus thrust (Present and Ambiguous) and the measured PVV was created, and the cut-off PVV for visualized varus thrust was determined as the highest point for both sensitivity and specificity. Results: The mean PVVs were significantly different between the three groups (Present, 47.7 ± 8.2 degree/s, Ambiguous, 34.1 ± 10.5 degree/s, and Absent, 28.1 ± 8.3 degree/s, respectively, ANOVA P=0.000). The PVV cut-off value for visualized varus thrust was 28.1 degree/s, yielding a sensitivity of 0.957 and a specificity of 0.579. Conclusions: A PVV <28.1 degree/s is useful for ruling out varus thrust during gait. This quantitative varus thrust assessment method using IMUs has clinical utility as a screening test.

Unicompartmental Knee Arthroplasty for Osteoarthritis Eliminates Lateral Thrust: Associations between Lateral Thrust Detected by Inertial Measurement Units and Clinical Outcomes

“…For gait analysis, IMUs (IMU-Z2, ZMP Inc., Tokyo, Japan) were attached to the waist, both thighs, and both lower legs with straps (Figure 1). As in previous studies, the sampling rate was 100 Hz [15].…”

“…For gait analysis, IMUs (IMU-Z2, ZMP Inc., Tokyo, Japan) were attached to the waist, both thighs, and both lower legs with straps (Figure 1). As in previous studies, the sampling rate was 100 Hz [15]. The subject walked 10 m three times while wearing an inertial sensor, and the average data were used.…”

“…As in the previous study, the internal and external angles of the knee joint were calculated using an extended Kalman filter, and the angular velocity of the knee was calculated by differentiating the calculated angles [16]. The cutoff value for the presence of lateral thrust was the knee internal rotation angular velocity of 28.1 • /s obtained in a previous study [15]. The study participants were asked to walk at their own comfortable pace along a 10 m walkway.…”

“…In contrast, inertial sensors can accurately record minute movements, such as lateral thrusts, in the form of acceleration. Tsukamoto et al were able to quantify lateral thrust in patients with knee OA using inertial measurement sensor units (IMUs) [15]. Using this method, if the change in lateral thrust can be quantitatively evaluated before and after UKA using IMUs, it will be possible to not only clarify that UKA can be performed for patients with instability that causes lateral thrust but also quantitatively show that lateral thrust improves after UKA surgery.…”

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

“…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 ].…”