Tibialis Posterior Muscle Morphology in Flexible Flatfeet Subjects

The goal of this observational study is to assess tibialis posterior muscle morphology in adults with flexible flatfeet. The main question it aims to answer is: Are there differences in tibialis posterior muscle morphology between adults with symptomatic flexible flatfeet, asymptomatic flexible flatfeet, and individuals with normal foot posture? Participants will undergo clinical assessment of foot posture and symptoms and an ultrasound assessment of the tibialis posterior muscle. The study will compare muscle thickness, cross-sectional area, and echo intensity among the three groups.

Inclusion Criteria: * Adults aged 18 to 40 years. * Both males and females will be eligible to participate. * Body mass index (BMI) ≤30 kg/m². * Participants with flexible flatfoot will demonstrate a visible medial longitudinal arch in the non-weight-bearing position and flattening of the arch during full weight-bearing. * Participants with flexible flatfoot will have a Foot Posture Index-6 (FPI-6) score of ≥+6. * Participants in the normal foot posture control group will have an FPI-6 score ranging from 0 to +5. * Participants must be able to stand and walk independently without an assistive device. * Participants must be willing to participate in the study and provide informed consent. Exclusion Criteria: * History of previous surgery involving the foot, ankle, or lower limb. * History of significant trauma or fracture involving the foot, ankle, or lower limb. * Presence of rigid flatfoot or other structural foot deformities. * Presence of neurological disorders affecting the lower limb. * Presence of neuromuscular disorders affecting the lower limb. * Presence of systemic or inflammatory musculoskeletal conditions affecting the lower limb. * Current lower-limb injury or condition that may affect standing, walking, foot posture, or tibialis posterior muscle morphology. * Pregnancy. * Participants who are unable to follow the assessment procedures or complete the required study measurements.