The Effect of Lateral Wedge and Medial Arch Support on Displacement of Ground Reaction Force in Patients with Knee Osteoarthritis

Osteoarthritis is a degenerative disease of joints that causes degeneration and corrosion of joint surface. Because of osteoarthritis, the smooth and even movemvement of joints get interrupted. Osteoarthritis is the most common kind of arthritis and its prevalence is 19.3% in Iran. Patients with knee osteoarthritis usually have geno varum and hyperpronation of foot. The purpose of the current study was to evaluate the effect of lateral wedge and medial arch support on displacement of ground reaction force in knee osteoarthritis in static state.
The current study is a quasi-experimental study. A total of 13 patients (9 women and 4 men) with an average(SD) age of 63.08±7.7 years with knee osteoarthritis were selected from available community. Four different test conditions, including 1) barefoot, 2) lateral wedge, 3) medial wedge, and 4) arch support and lateral wedge were conducted. L.A.S.A.R Posture was used to assess the changes of ground reaction force from knee center and the comfort level after the intervention was measured on a visual analog scale. The changes of lever arm were measured with the instrument and the obtained data were analyzed by SPSS version 20, through multivariate analysis and Bonferroni tests.
The result indicated that lateral wedge caused a significant decrease in ground reaction vector from knee center in barefoot condition (P=0.005). The average distance of weight line from knee center were -13.6 in without arthritis condition, -0.8 with lateral wedge, -11.8 with medial arch, and -7 with lateral wedge with medial arch. Therefore, using the lateral wedge with 7 mm thickness displace the path of ground reaction force on the knee, in such a way that the lever arm of ground reaction force from knee center (which produces adductor torque on the knee) with putting 12.8 mm lateral wedge has become smaller that of barefoot condition. With regard to comparing different conditions, no significant differences were observed between barefoot, medial arch, and combination of medial arch with lateral wedge. However, there was a significant difference between lateral wedge and medial arch (P=0.013), so that the lever arm of ground reaction force with lateral wedge is 11 mm shorter. Also, comparing lateral wedge with arch and lateral wedge showed that lateral wedge is 6.2 mm shorter or it creates 88.5% shorter lever arm (P=0.001). No significant difference was seen between conditions of medial arch and combination of arch with lateral wedge.
Given the results, using the lateral wedge decreases the lever arm of ground reaction force to the knee center in people with knee osteoarthritis and geno varum and hyperpronation of foot. Moreover, adding medial arch reduces the effect of lateral wedge on shortening lever arm of ground reaction force on the knee and as a result reduces knee adductor torque in patients with knee osteoarthritis. However, lateral wedge, medial arch, or their combination have no statistically significant effect on the comfort of these patients.