Objective To investigate the biomechanical differences in plantar pressure, postural stability, and plantar Visual Analogue Scale (VAS) scores between normal feet and unilateral/bilateral pes cavus, reveal their unique neuromechanical compensation mechanisms, and construct a stability early warning model based on the minimum center of pressure (COP) trajectory classification.

Methods A total of 70 patients with pes cavus from December 2023 to October 2024 were selected as study subjects, including 33 patients in the unilateral pes cavus group and 37 patients in the bilateral pes cavus group. During the same period, 32 normal feet were included as normal foot group. A flat-panel plantar pressure testing system was used to collect dynamic plantar pressure data and COP trajectories from three groups at a self-selected walking speed. There were no statistically significant differences in baseline data such as age, gender, and body mass index among the three groups (P>0.05). One-way analysis of variance and the Wilcoxon rank-sum test were used to compare the differences in maximum pressure, contact area, VAS scores, and the 95% confidence ellipse area of the COP among the three groups in 10 plantar regions.

Results Patients with pes cavus exhibited lower peak pressure in the MF region compared to normal feet, while higher peak pressure in the M2, M3, and MH regions. Patients with bilateral pes cavus showed lower peak pressure in the T1 region compared to normal feet, and patients with unilateral pes cavus had lower peak pressure in the LH region compared to the normal group (P < 0.05). The plantar contact area in patients with pes cavus was reduced in the T1, M2, M3, M4, MF, and MH regions compared to normal feet (P < 0.05). The 95% confidence ellipse area of the COP was larger in both the bilateral and unilateral pes cavus groups compared to the normal foot group (P < 0.001). Unilateral pes cavus presented a specific lateral COP drift (amplitude of 3 to 4 cm), which is a biomechanical manifestation of compensatory eversion of the unaffected foot. Patients with bilateral pes cavus exhibited a "bimodal oscillation" trajectory (amplitude of 6 to 8 cm), suggesting possible vestibular-spinal regulatory dysfunction and the poorest postural stability. In the pes cavus group, there was a significant increase in pressure in the M2, M3, and MH regions, with peak pressures exceeding 190 kPa in patients with bilateral pes cavus, which was highly correlated with plantar pain and could serve as a pain early warning threshold.

Conclusion Unilateral and bilateral pes cavus exhibit significantly different neuromechanical compensation patterns. The classification based on the "lateral drift" and "bimodal oscillation" characteristics of the COP trajectory can serve as a stability early warning indicator for assessing fall risk. Decompression interventions targeting the key pressure regions of M2, M3, and MH (such as customized orthotic insoles) are the core strategies for alleviating pain and optimizing dynamic gait stability.