Lateral Coronal Bowing of Femur and/or Tibia Amplifies the Varus Malalignment of Lower Limb as well as Increases Functional Disability in Patients with Knee Osteoarthritis.

PURPOSE: In the present study, we aimed at assessing the effect of femoral and tibial coronal bowing on varus malalignment and Oxford knee score (OKS) at different grades of knee osteoarthritis (OA).
MATERIALS AND METHODS: This prospective observational study was conducted at a tertiary referral centre in New Delhi, India. Consecutive patients presenting to the "knee OA" outpatient clinics were invited to take part in the study conducted over a 12-month period. All consented patients underwent long-leg standing alignment radiographs using standardised technique and patient reported knee pain and function were recorded using Oxford knee score. The following radiological parameters were measured from weight-bearing long-leg radiographs of 824 varus aligned limbs via a morphometric software (Matlab R2009a) (1) hip-knee-ankle angle (HKAA), (2) femoral bowing, (3) tibial bowing. The knees were graded according to Kellegren and Lawrence grade (K&L) and OKS was recorded. 3 groups of HKAA were made based on the angle, A (0° to - 3°), B (- 3° to - 10°) and C (< - 10°). Both the femoral and tibial bow were also categorized into three groups depending upon the angle; in-range (- 2° to + 2°), varus (< - 2°), valgus (> + 2°).
RESULTS: The mean (± SD) of HKAA, femoral bow and tibial bow of the whole cohort was - 6.97° ± 5.64°, - 1.54° ± 4.31° and - 1.96° ± 3.5°, respectively. An increase in the lateral bow of both femur and tibia was seen with an increase in the severity of OA. A consequent increase in the varus malalignment was observed with an increase in the lateral bow of both femur as well as the tibia at all grades of OA, with significant correlation observed between HKAA with Femoral bowing and HKAA with tibial bowing. The mean OKS for femoral bow, in-range, varus and valgus was 30.6 ± 11.5, 21.3 ± 11.5 and 35.3 ± 11.4, respectively, and for tibial bow, in-range, varus and valgus was 27.6 ± 11.5, 26. ± 11.5 and 28 ± 11.4, respectively. The difference in the mean OKS was observed to be significant when the varus bow group was compared to in range as well as valgus group (p < 0.01) for both femur and tibia for all the grades of OA.
CONCLUSION: The present study shows a significant correlation between varus malalignment and the bowing of extremities. Varus coronal bowing of both femur and tibia were seen to have significantly lower mean OKS as compared to valgus bowing or in-range bowing at all grades of knee OA. © Indian Orthopaedics Association 2020.