Varus Knee Limits Pain Relief Effects of Laterally Wedged Insoles and Ankle-Foot Orthoses in Medial Knee Osteoarthritis.

Abstract

To investigate the impact of varus malalignment of the knee on pain reduction achieved by an ankle-foot orthosis and a laterally wedged insole in patients with medial knee osteoarthritis. Secondary analysis of a randomized, clinically prospective cross-over study. Twenty-eight participants with medial knee osteoarthritis. All participants wore a 5-mm laterally wedged insole and an ankle-foot orthosis for a period of 6 weeks each in a randomized order. Pain was reported on a numerical rating scale and was correlated with limb alignment, as defined by the mechanical axis deviation in full-leg standing radiographs. Insole and orthosis use reduced pain compared with baseline (median knee pain change: insole -0.5 (-5 to +6), orthosis -1.5 (-7 to +5). A higher mechanical axis deviation (greater varus) correlated significantly with smaller pain reduction for both aids (insole p = 0.003, orthosis p < 0.001). A cut-off to predict pain response was found at a mechanical axis deviation of 14-15 mm for both aids, i.e. > 3° knee varus. There is a correlation between varus malalignment and pain reduction. There seems to be a mechanical axis deviation cut-off that predicts the response to treatment with the aids with good sensitivity.