Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


Varus Thrust and Knee Frontal Plane Dynamic Motion in Persons with Knee Osteoarthritis.

Chang,  Alison, Chmiel,  Joan, Moisio,  Kirsten, Almagor,  Orit, Zhang,  Yunhui, Cahue,  September, Saurel,  Clifton

Background/Purpose:

Varus thrust visualized during walking is associated with a greater peak external knee adduction moment and an increased likelihood of medial knee osteoarthritis (OA) disease progression. Gait observation for a thrust is a simple and inexpensive clinical screening tool that enables identification of some individuals at higher risk for disease progression. How observed varus thrust relates to quantitative gait kinematic data is not known. We hypothesized that varus thrust presence is associated with greater knee frontal plane dynamic movement during the stance phase of gait.

Methods:

Participants all had knee OA (by osteophyte presence) in at least one knee. Knee motion in the frontal plane during ambulation on a 35 × 4 foot walkway was captured at a rate of 120 Hz, using external passive reflective markers and an 8-camera Digital Real-Time Eagle motion analysis system. Frontal plane motion was measured using the peak knee varus angle during stance (and each subdivision of stance), peak knee varus angular velocity, and total knee varus-valgus motion during stance. Following a protocol and blinded to the knee frontal plane motion data, trained examiners assessed participants for varus thrust presence during ambulation in a 10-meter walkway. To examine the relationship between varus thrust and frontal plane knee dynamic motion, we used multivariable regression analysis with generalized estimating equations (GEE) to account for correlations between knees within persons; presence of thrust was coded using an indicator variable. Models were adjusted for age, gender, BMI, and gait speed. Findings are reported as mean differences between knees with vs. without thrust and 95% confidence intervals (CIs).

Results:

The study sample consisted of 236 persons [mean age 64.9 (SD 10.4), BMI 28.5 (5.5), 179 (76%) women] contributing 440 knees for analysis. 82 knees (19%) had a definite varus thrust. Table 1 shows the mean (SD) for each frontal knee motion measure. As shown in Table 2, knees with varus thrust had a greater peak knee varus angle during the entire stance and each sub-phase as well as greater peak knee varus angular velocity.

Table 1. Means (SDs) Knee Frontal Plane Quantitative Motion Measures during Gait by Varus Thrust Status

Measures of frontal plane motion during gaitAll knees n = 440 Mean (SD)Knees with varus thrust n = 82 Mean (SD)Knees without varus thrust n = 358 Mean (SD)
Peak knee varus angle during stance (°)1.77 (1.28)2.51 (1.55)1.60 (1.15)
Peak knee varus angle during early stance (°)0.72 (0.98)1.55 (1.29)0.53 (0.79)
Peak knee varus angle during mid-stance (°)1.32 (1.50)2.27 (1.64)1.10 (1.38)
Peak knee varus angle during terminal stance (°)1.42 (1.22)2.03 (1.47)1.28 (1.11)
Peak knee varus angle during pre-swing (°)-0.16 (1.51)0.66 (1.67)-0.35 (1.40)
Peak knee varus angular velocity (°/sec)0.29 (0.16)0.36 (0.15)0.28 (0.16)
Total knee varus-valgus range of motion (°)8.69 (3.37)8.53 (3.07)8.72 (3.44)

Table 2. Estimated Differences in Means for Knee Frontal Plane Motion Measures Based on Presence vs. Absence of Varus Thrust, from the GEE Regression Models

Measures of frontal plane motion during gaitDifference* (95% confidence interval)
 UnadjustedAdjusted for age, gender, and BMIAdjusted for age, gender, BMI, and gait speed
Peak knee varus angle during stance (°)0.91 (0.52, 1.30)0.97 (0.56, 1.37)0.98 (0.57, 1.38)
Peak knee varus angle during early stance (°)1.02 (0.68, 1.35)1.03 (0.69, 1.38)1.04 (0.70, 1.38)
Peak knee varus angle during mid-stance (°)1.16 (0.73, 1.60)1.31 (0.85, 1.77)1.30 (0.84, 1.77)
Peak knee varus angle during terminal stance (°)0.75 (0.36, 1.14)0.82 (0.42, 1.23)0.83 (0.43, 1.23)
Peak knee varus angle during pre-swing (°)1.01 (0.56, 1.45)0.94 (0.48, 1.41)0.94 (0.48, 1.41)
Peak knee varus angular velocity (°/sec)0.08 (0.04, 0.12)0.08 (0.04, 0.12)0.08 (0.04, 0.12)
Total knee varus-valgus range of motion (°)-0.19 (-0.96, 0.58)0.40 (-0.39, 1.20)0.45 (-0.34, 1.23)
* Positive difference indicates greater mean value for knees with varus thrust vs. those without varus thrust. 95% CI that excludes 0 indicates a statistically significant difference between the groups.

Conclusion:

Knees with a varus thrust during gait had greater peak knee varus angle and knee varus angular velocity during stance than knees without a thrust. These findings provide evidence that visualized varus thrust is associated with objective and quantitative measures of dynamic frontal plane instability.

To cite this abstract, please use the following information:
Chang, Alison, Chmiel, Joan, Moisio, Kirsten, Almagor, Orit, Zhang, Yunhui, Cahue, September, et al; Varus Thrust and Knee Frontal Plane Dynamic Motion in Persons with Knee Osteoarthritis. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :1085
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