Investigation of foot function, pain, flexibility and muscular performance levels according to the degree of pes planus in patients with plantar fasciitis: a cross-sectional study

Objective: The aim of this study was to investigate how the degree of pes planus (PP) affects pain, flexibility, muscle performance, and foot functionality in individuals with plantar fasciitis (PF). Material and Methods: The study included 58 individuals with PF. Participants were divided into three groups based on their PP degrees determined by the Feiss line test: '0' (no PP), '1' (Grade 1 PP) and '2' (Grade 2 PP). Pain intensity was assessed using the Visual Analog Scale (VAS), flexibility was evaluated using gastro-soleus and plantar fascia flexibility tests, muscle performance was measured using the Heel Rise test, and foot functionality was assessed through the Foot Function Index (FFI). Results: No differences were found among the groups in terms of pain intensity, gastro-soleus flexibility, muscle performance, and foot functionality (p>0.05). A significant difference was observed in plantar fascia flexibility between groups '0' and '1', with greater flexibility in the group without PP compared to those with Grade 1 PP (p=0.024); groups '0'-'2' and '1'-'2' revealed similar results (p=0.431; p=0.494). Conclusion: The degree of PP appears to have a limited impact on pain, gastro-soleus flexibility, muscle performance, and foot functionality in individuals with PF, although it may affect plantar fascia flexibility. Current evidence is insufficient to support treatment modifications based solely on PP degree. Future studies with larger samples and objective biomechanical assessments are needed to further clarify these relationships.