Varus malalignment and its association with impairments and functional limitations in medial knee osteoarthritis

Abstract

To examine the association of varus malalignment with impairments and functional limitations in people with medial knee osteoarthritis (OA). Anatomic radiographic knee alignment was assessed in 107 community volunteers with medial tibiofemoral knee OA. Impairments assessed included pain (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]), quadriceps and hamstring isometric strength, and knee varus-valgus laxity. WOMAC, walking speed, step test, and stair climb test were used to assess functional limitations. Participants were categorized into tertiles according to knee alignment (least, moderate, and most varus). Impairments and functional limitations between groups were compared using analyses of variance with and without adjustment for age, sex, and disease severity. Regression analyses were also performed in the entire cohort to further determine the relationship of varus malalignment to impairments and functional limitations. The most varus group (mean varus 7.7 degrees) did not demonstrate greater impairments or worse functional limitations compared with the moderate varus (4.2 degrees) and least varus (5.0 degrees) groups. In fact, the most varus participants performed significantly better on the step test compared with moderate (P = 0.006) and least varus (P = 0.004) participants. Knee alignment accounted for a significant but small proportion of the variance in step test performance (7%) and quadriceps strength (4%), but did not contribute significantly to the variance in any other parameter measured. Greater varus malalignment was associated with increased quadriceps strength and improved step test performance, but did not influence the severity of other measured impairments and functional limitations.