The influence of sole wedges on frontal plane knee kinetics, in isolation and in combination with representative rigid and semi-rigid ankle–foot-orthoses

Background In earlier stages of knee osteoarthritis orthotic treatments with knee orthoses or modified footwear are often considered. Although the load reducing effects of knee orthoses have been well established, wearing modified footwear would be more comfortable for the patient and less encumbering. The effect of modified footwear on the frontal load of the knee is controversial. This article describes the effect of medial or lateral shoe wedges alone or together with two different types of ankle-stabilizing orthoses. Methods The effect on frontal knee loading was measured during standing and walking with medially and laterally placed wedges under the sole of the shoe. The wedges were also combined with two types of orthotic devices – an Ankle–Foot-Orthosis that was rigid in the frontal plane but allowed unrestricted sagittal plane motion and an ankle support that was semi-rigid in the frontal plane. Joint loading of 10 healthy persons (mean (standard deviation): age 34 (9) years, height 178 (4) cm, mass 73 (9) kg) was investigated by means of a special measuring device that accurately determines static loads (Lasar Posture) and with instrumented gait analysis (Vicon/Kistler). Findings Using a lateral wedge under the sole of the shoe (without orthotic support) showed no significant reduction in the mean maximal knee moment in the frontal plane. Adding an Ankle–Foot-Orthosis that is rigid in the frontal plane resulted in significant reduction in the maximal frontal moment from 0.54 N m/kg to 0.38 N m/kg (p less-than-or-equals, slant 0.01). Using a medial wedge, without and with Ankle–Foot-Orthosis, produced a significant increase in the maximal frontal moment to 0.59 N m/kg (p less-than-or-equals, slant 0.05) or 0.67 N m/kg (p less-than-or-equals, slant 0.01), respectively. Interpretation These results suggest that the application of a sole wedge significantly influences frontal knee loading when used in combination with an Ankle–Foot-Orthosis that is rigid in the frontal plane.