Background/Purpose: Varus knee thrust is an abrupt change in frontal plane tibiofemoral alignment observed during gait. Thrust has been linked to radiographic knee OA progression and worsening cartilage and bone marrow lesions. In addition, thrust has been cross-sectionally linked to knee pain presence during weight-bearing. Our objective was to determine the longitudinal effect of knee thrust on worsening knee pain over 2 years in older adults with or at risk for OA.

Methods: The Multicenter Osteoarthritis Study (MOST) is a prospective cohort study of older Americans with or at risk for knee OA. At the 60-month clinic exam, 60 Hz frontal plane videos recorded participants completing two self-paced walking trials over a 4.9 meter walkway. A trained reader, blinded to disease status, assessed the presence of varus thrust on a majority of steps (intra-rater κ = 0.73). Pain in each knee while walking, using stairs, standing upright, sitting, and in bed was assessed using the WOMAC questionnaire at 60 and 84 months. Among knees with submaximal WOMAC scores at 60 months, worsening pain at 84 months was defined as any increase in WOMAC score, and clinically important worsening was defined as an increase of ≥ 1.28 in WOMAC score. To assess the relation of thrust to worsening knee pain, we used logistic regression with generalized estimating equations to account for non-independent limbs from a subject, adjusting for age, sex, race, BMI, and gait speed. We repeated the analysis on a subset of knees with baseline WOMAC scores of 0 to assess the relation of thrust to incident WOMAC knee pain. We also assessed the relation of thrust to worsening knee pain in a subset of knees without baseline radiographic OA (Kellgren-Lawrence (KL) Grade < 2).

Results: 1623 participants (mean age 67.2 ± 7.6 years, mean BMI 30.4 ± 5.9, 59.9% female, 88.7% White) contributed 3204 knees. Varus thrust was observed in 31.5% of knees. At baseline, mean total WOMAC pain was 2.40, and 41% of knees had radiographic knee OA (KL ≥ 2). Knees with a varus thrust had 1.45 (95% CI: 1.22, 1.72) and 1.46 (95% CI: 1.20, 1.77) times the odds of any worsening and clinically important worsening total WOMAC pain, respectively, compared to knees without thrust; this increased pain was consistent across all WOMAC listed activities (see Table) and among the subset of knees without radiographic knee OA at baseline (OR = 1.39; 95% CI: 1.06, 1.82). Among knees with no WOMAC pain at baseline, knees with thrust had 1.81 times the odds (95% CI: 1.35, 2.41) of incident pain at two years compared to knees without thrust.

Conclusion: Varus knee thrust observed during walking is associated with increased odds of worsening knee pain during both weight-bearing and non-weight-bearing activities in older adults with or at risk for OA. Given that thrust is potentially modifiable using non-invasive therapies, detecting thrust provides an opportunity to prevent worsening knee pain in these populations.