To determine if varus thrust, a bowing out of the knee during gait (i.e., the first appearance or worsening of varus alignment during stance), is associated with incident and progressive knee osteoarthritis (OA), these researchers undertook an Osteoarthritis Initiative ancillary study. They also considered hypothesized associations adjusted for static alignment, anticipating some attenuation.
Methods: Gait was observed for the presence of thrust by examiners at four sites. In eligible knees, incident OA was analyzed as subsequent incident Kellgren/Lawrence grade ≥2, whole- and partial-grade medial joint space narrowing (JSN) and annualized loss of joint space width (JSW). Progression was analyzed as medial JSN and JSW loss. Outcomes were assessed for up to seven years of follow-up. Analyses were knee-level, using multivariable logistic and linear regression with generalized estimating equations to account for between-limb correlation.
Results: The incident OA sample included 4,187 knees (2,610 people); the progression sample included 3,421 knees (2,284 people). In knees with OA, thrust was associated with progression by each outcome adjusting for age, sex, body mass index and pain on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). In knees without OA, varus thrust was not associated with incident OA or other outcomes. After adjustment for alignment, the thrust/progression association was attenuated, but an independent association persisted for partial grade JSN and JSW loss outcome models. WOMAC pain and alignment were consistently associated with all outcomes. Within the stratum of varus knees, thrust was associated with an increased risk of progression.
Conclusion: Varus thrust visualized during gait is associated with knee OA progression and should be a target of intervention development.
What This Means: These findings have important research and clinical implications. This study replicates previous findings that varus thrust is associated with knee OA progression. Although specific development is needed, it’s not difficult to envision an orthotic approach to help stabilize the knee. Of note, to relieve pain, neuromuscular exercise was more effective for individuals with a varus thrust, and quadriceps strengthening exercise was more effective when a thrust was absent.
Future studies could focus on developing and evaluating a training video or other approach to disseminate gait observation training. Gait observation can be incorporated into observational and therapeutic studies of knee OA to enable analytic consideration of thrust. Gait observation cannot replace quantitative gait analysis, but it does provide a simple approach to identify individuals at higher risk of progression. The findings are a reminder of the powers of observation.