Background
Knee osteoarthritis (KOA) is a degenerative progressive joint disease characterized by chronic joint pain and stiffness, leading to the limitation of daily living activities and physical function. Given the important role of the foot in receiving and distributing forces during walking, foot characteristics and mechanics may significantly contribute to musculoskeletal conditions of the lower limb. However, the specific associations between foot characteristics and mechanics and KOA have not yet been investigated. The purpose of this study is to identify the plantar pressure pattern during walking in patient with medial KOA.
Methods
Twenty patients (10 males, 10 females, 60.9 y.o.) who diagnosed with medial knee OA were included in this study. All patients were scheduled for around knee osteotomy for medial KOA. The in-shoe plantar pressure evaluation system, which has 10 plantar pressure sensors were implanted in a 1-mm thick insole, was used for measurement. Plantar pressure of both feet were recorded with 200?Hz during walking at least 10 steps at a comfortable speed. The peak pressure during walking were analyzed in each sensor, and the results were compared between different areas of the foot in the antero-posterior (AP) direction (toes, forefoot, midfoot and hindfoot) and the medio-lateral (ML) direction (medial and lateral). The length of the center of pressure (COP) in AP and ML direction during walking were also calculated. The relationship between the plantar pressure and X-ray parameters (%mechanical axis, the hip-knee-ankle angle, mechanical medial proximal tibial angle, and the joint line convergence angle) and Knee injury and Osteoarthritis Outcome Score (KOOS) were evaluated.
Results
The average of the hip-knee-ankle angle were 7.6 degree (range: 2.0 to 15.0) varus on affected side and 2.7 degree (-4.2 to 10.0) varus on contralateral side. On both the affected and contralateral sides, the plantar pressure center shifted in the order of hindfoot, midfoot, forefoot, and toes. The peak pressure on the affected side was significantly lower in toes (p=0.05) and tended to be lower in the midfoot, forefoot, and hindfoot (p=0.13, 0.20, 0.31) than on the contralateral side. There was no significant difference in the length of the COP in AP direction between the affected side and the contralateral side, but it was significantly shorter in the length of the COP in ML direction on the affected compared to contralateral side (p=0.05). No relationship was found between the X-ray parameters and the length of the COP in AP and ML direction. There was a positive correlation between the KOOS and the length of COP in ML direction (r=0.67, p=0.004).
Conclusions
Plantar pressure pattern during walking in patient with medial knee osteoarthritis was evaluated using an in-shoe plantar pressure evaluation system. The COP translated in the order of hindfoot, midfoot, forefoot, and toes, and the loading pattern was similar to that of healthy subjects reported previously. It was suggested that patients with medial KOA may not be able to bear enough weight on the toes compared to contralateral side, and they may walk with less movement of the COP in ML direction to avoid knee pain.