Varus thrust and knee frontal plane dynamic motion in persons with knee osteoarthritis

Abstract

Objective: Varus thrust visualized during walking is associated with a greater medial knee load and an increased risk of medial knee osteoarthritis (OA) progression. Little is known about how varus thrust presence determined by visual observation relates to quantitative gait kinematic data. We hypothesized that varus thrust presence is associated with greater knee frontal plane dynamic movement during the stance phase of gait.

Methods: Participants had knee OA in at least one knee. Trained examiners assessed participants for varus thrust presence during ambulation. Frontal plane knee motion during ambulation was captured using external passive reflective markers and an 8-camera motion analysis system. To examine the cross-sectional relationship between varus thrust and frontal plane knee motion, we used multivariable regression models with the quantitative motion measures as dependent variables and varus thrust (present/absent) as predictor; models were adjusted for age, gender, body mass index (BMI), gait speed, and knee static alignment.

Results: 236 persons [mean BMI: 28.5 kg/m(2) (standard deviation (SD) 5.5), mean age: 64.9 years (SD 10.4), 75.8% women] contributing 440 knees comprised the study sample. 82 knees (18.6%) had definite varus thrust. Knees with varus thrust had greater peak varus angle and greater peak varus angular velocity during stance than knees without varus thrust (mean differences 0.90° and 6.65°/s, respectively). These patterns remained significant after adjusting for age, gender, BMI, gait speed, and knee static alignment.

Conclusion: Visualized varus thrust during walking was associated with a greater peak knee varus angular velocity and a greater peak knee varus angle during stance phase of gait.

Keywords: Gait analysis; Instability; Knee osteoarthritis; Varus thrust.

Figure 1

Frontal plane knee angle (figure a) and angular velocity (figure b) curves during the first 60% of gait cycle (mainly stance phase of walking) in knees with visually observed varus thrust (red line) vs. knees without thrust (black line). Varus is in the positive direction. Solid lines represent the ensemble averages and shaded areas represent ± one standard deviation around the average values. The initial knee position at the beginning of stance was normalized to “zero” for ease of comparison. In the varus thrust positive group, the maximum knee varus angle occurred near the beginning of the mid stance phase for the ensemble average curve, and remained near the maximum throughout the entire mid stance phase, eventually returning to baseline at the end of stance. Note the corresponding greater increase of knee varus angular velocity. It is important to point out that each knee’s peak varus angle and angular velocity occurred at a slightly different time point during the early to mid stance phase of gait, and thus averaging these magnitudes at each time point likely will attenuate the individual knees’ peak values. Nonetheless, the general trend of greater knee varus angle and angular velocity is evident in knees with a varus thrust compared to knees without a varus thrust.