Background/Purpose: Lateral wedge foot orthosis have been used therapeutically in patients with medial knee osteoarthritis (OA) with inconsistent results. The current theory suggests they reduce medial knee loading by shifting the ground reaction force vector, and thereby potentially modify progression of OA. Predicting a beneficial result from usage of lateral wedge orthotics is crucial since results to-date suggest that responses in large groups of subjects are heterogeneous.  We aimed to investigate radiographic parameters in patients with medial knee OA that might prospectively distinguish those who benefit from lateral wedge from those who do not.

Methods: Participants (n=109) with radiographic (KL grades 2-3) and symptomatic (at least 30mm pain of 100 mm scale while walking) medial compartment knee OA were enrolled in a previously reported 36 month double blind study to clinically assess a 7 degree lateral wedge custom foot orthosis versus a neutral 0 degree posted control. In the current study, 35 patients in the lateral wedge arm who had complete data were included. Subjects underwent gait analyses. Post hoc analysis identified a group as ‘unloaders’ if knee adduction moments gradually decreased over time with the use of wedge.  Image J software (US NIH, Bethesta, MD, http://rsbweb.nih.gov/ij/) was used to measure radiographic parameters that included: knee alignment angle, tibial shaft angle measured at three levels: from tibial plateau to the tibial plafond (long axis), from mid tibial level to plafon and from lower third of tibia to plafond (lower axis), as well as the narrowest joint space widths of the hip, knee and ankle joints. The difference between the varus angle of tibial long axis and tibial lower axis was calculated for each patient to estimate the varus angulation of the distal 1/3 of the tibial shaft. Correlations of radiographic parameters were analyzed in the entire group. Non-parametric tests were used for statistical analysis to compare groups. A p value of ≤ 0.05 was considered significant.

Results: Twenty patients were classified as ‘unloaders’ while 15 were noted to be unresponsive to the therapy.  These responsive unloaders had larger distal tibial varus angle compared to those who did not have significant reduction in knee adduction moments with lateral wedge (median(IQR) 1.3(0.8) vs. 0.6(1.5) degrees, respectively, p=0.042). None of the other radiographic parameters studied differed between those who benefitted from lateral wedge and those who did not. Importantly, assessment of the difference between the tibial long axis and the lower one third tibial axis (lower angle minus long axis) revealed a significant correlation with the knee alignment angle (r=0.26, p=0.01).

Conclusion: The correlation between the knee alignment angle and the difference between tibial long axis and lower one third tibial axis suggests that as the knee presents with more varus, there is a varus bend in the lower tibia. Specifically, curvature of the lower tibia appears to be the primary varus deformity seen in the lower extremity with medial knee OA.  These results suggest that distal tibial varus could be a radiographic parameter predicting a beneficial result from a lateral wedge orthotic in patients with medial knee OA.

---

« Back to 2013 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/predicting-benefit-from-lateral-wedge-orthotics-using-radiographic-parameters-in-medial-knee-osteoarthritis/