Chang AH, Hayes KW, Dunlop DD, Song J, Cahue S, Sharma L; Northwestern University, Feinberg School of Medicine, Chicago, IL. hsini@northwestern.edu.

PURPOSE: Varus thrust (VT) is a lateral knee motion that occurs in the stance limb during ambulation, producing the acute appearance or worsening of varus alignment. VT reflects dynamic mal-alignment, instability, and, in theory, an acute increase in medial tibiofemoral compartment loading during the stance phase of gait. We tested the hypothesis that VT observed during gait at baseline increases the risk of medial knee OA progression over the next 18 months. SUBJECTS: 222 participants (73% women, mean age 68, mean BMI 30) with mild to moderate knee OA (by definite osteophytes and symptoms) were followed for 18 months. Excluding knees with advanced OA at baseline, we analyzed 401 knees. METHODS: Baseline assessments included observation of the presence of VT during gait, knee varus/valgus alignment (hip/knee/ankle angle from full limb radiograph), and BMI. To assess disease progression by joint space narrowing, semi-flexed, fluoro-guided AP knee x-rays were obtained at baseline and at 18 months. Medial joint space narrowing was graded 0 (none) to 3 (severe) and progression was defined as worsening of grade of medial joint space narrowing from baseline to 18 months. ANALYSIS: Logistic regression with general estimating equations (knee-based analysis) were used to estimate odds ratios (OR) for medial OA progression. RESULTS: Of the 401 knees, 67 had VT at baseline. Compared with knees without VT, knees with VT were more severely varus (3.30° varus vs. 1.14° valgus, p < .0001) and had greater loss of medial joint space over 18 months (0.20 vs. 0.007 mm). VT was associated with a 4-fold increase in the likelihood of medial OA progression over 18 months (age, gender, BMI-adjusted OR 3.97, 95% CI [2.13, 7.41]). Results were not altered by adjusting for baseline disease severity and were similar using worsening of K/L grade to define progression. CONCLUSIONS: The presence of VT in gait observation at baseline increased the risk of medial OA progression over the ensuing 18 months. VT is a simple, quick, and inexpensive way to capture knee dynamic mal-alignment and excessive medial compartment loading. It does not require any special equipment and can be performed as part of the clinical examination to identify individuals at risk of medial OA progression. Whether interventions, such as bracing, valgus-wedged soles or dynamic muscle stabilization, lessen varus thrust and delay medial OA progression should be examined in future studies. FUNDING SOURCE: National Institute of Health – AR48098, AR48216.

Copyright 2004 by the American Physical Therapy Association

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