Effectiveness of a lateral-wedge insole on knee varus torque in patients with knee osteoarthritis

Objectives: To test whether a lateral-wedged insole, inclined at 5 degrees or 10 degrees, significantly reduces knee varus torque during walking in patients with knee osteoarthritis compared with both using no insole and with wearing nonwedged control insoles of the same material and average thickness.

Design: Patients with medial knee osteoarthritis were studied while they walked wearing their comfortable shoes (1) without an insole; (2) with a 5 degrees lateral wedge compared with a nonwedged, 3.175-mm (1/8-in) even-thickness control insole; and (3) with a 10 degrees lateral wedge compared with a nonwedged 6.35-mm ((1/4)-in) even-thickness control insole.

Setting: A gait laboratory with 3-dimensional motion analysis and force platform equipment.

Participants: Fifteen patients with clinical and radiographic osteoarthritis of the medial compartment of 1 knee.

Interventions: Not applicable.

Main outcome measures: Peak external knee varus torques during the stance period of gait. Data regarding lower-extremity joint torques and motions were collected, and knee joint torques using the different insoles and wedges were compared by analysis of variance.

Results: Although responses varied among individuals, as a group, both the 5 degrees and 10 degrees lateral-wedge insoles significantly reduced the knee varus torque during walking compared with walking with no insole and walking with nonwedged 3.175-mm and 6.35-mm control insoles. Compared with no insole, the 5 degrees wedge reduced the peak knee varus torque values by about 6% and the 10 degrees wedge reduced the peaks by about 8%. Although there were no significant differences in speed of walking between the conditions, the 10 degrees wedge and 6.35-mm control insoles were associated with varying degrees of discomfort.

Conclusion: Both wedge insoles are effective in reducing the varus torque during walking beyond what theoretically could be explained by a reduced walking speed or cushioning effect from the insole. These data imply that wedged insoles are biomechanically effective and should reduce loading of the medial compartment in persons with medial knee osteoarthritis. Although the effect of the 5 degrees wedge was smaller, it may be more comfortable than the 10 degrees wedge to wear inside one's own shoes.