Abstract: BACKGROUND: Plantar pressure is the reaction force exerted by the plantar region in the vertical direction under the action of gravity when the human body is standing still or walking dynamically. Correlation analysis of plantar pressure at different stages of knee osteoarthritis may provide evidence for early intervention and guidance of conditioning for knee osteoarthritis.  
OBJECTIVE: To investigate the changes of plantar pressure in different stages of unilateral knee osteoarthritis, and to provide relevant basis for the occurrence and development of unilateral knee osteoarthritis.
METHODS:  Unilateral knee osteoarthritis patients in the Department of Orthopedics and Traumatology, the Third Affiliated Hospital of Yunnan University of Chinese Medicine from October 2018 to December 2019 were collected for clinical staging according to clinical symptoms combined with radiology Kellgren-Lawrence classification, including 29 cases in the early stage, 32 cases in the middle stage and 27 cases in the later stage. LorAn plantar pressure tester was used to collect plantar pressure. Static pressure included anterior pressure, posterior pressure, left pressure, right pressure ratio and pelvic rotation. The dynamic pressure was taken as “characteristics of footsteps”, including pressure ratio in thumb, 2nd-5th toe (T2-5), 1st-5th (M1-5) metatarsal, middle foot, medial heel and lateral heel, to study the correlation between clinical staging and plantar pressure.  
RESULTS AND CONCLUSION: (1) In the static pressure distribution, there were significant differences in left pressure, right pressure and pelvic rotation among the three groups (P < 0.05). There were significant differences in T1, T2-5, M2, M5 and lateral heel on the affected side and M2, M3 and M4 on the healthy side (P < 0.05). (2) In static pressure, left pressure, right pressure, pelvic rotation and dynamic “characteristic foot” on M5, middle foot, and lateral heel of the affected side, and M2, M3, and M4 on the healthy side were positively correlated with clinical stage (P < 0.05). (3) In the static pressure, the left pressure and the right pressure, as well as the dynamic “characteristic feet” on the T1 and T2-5 of the affected side were negatively correlated with the clinical stage (P < 0.05). (4) The ordered multiple Logistic regression analysis showed that T2-5, M5, lateral heel and M3 on the affected side of characteristic feet were independent factors influencing clinical stages of knee osteoarthritis (β=-0.329, 0.333, 0.199, 0.654; P < 0.05). (5) The results showed that with the progression of knee osteoarthritis staging, the distribution of “static pressure” gradually tended to the uninjured side, and the rotation degree of the pelvis gradually increased to increase the compensatory capacity of the foot. The “dynamic pressure” on the affected side was distributed outward, and the pressure proportion of T1-5 was reduced, which provided stronger motivation for the departure stage. The “dynamic pressure” of the healthy side is distributed forward and outward to promote the center of gravity to move forward and reduce the load of the affected side knee joint.

Key words: knee, osteoarthritis, disease staging, gait analysis, plantar pressure