Background:

Pes planus, commonly known as flatfoot, is a condition characterized by the collapse of the medial longitudinal arch of the foot. While some individuals remain asymptomatic, many experience foot or leg pain, walking difficulties, and functional limitations. In some cases, symptoms persist despite adequate conventional treatment. This suggests that central pain mechanisms, such as central sensitization and nociplastic pain, may contribute to ongoing symptoms. These mechanisms involve changes in the central nervous system that amplify pain perception and can occur even in the absence of active tissue damage. Understanding these mechanisms in pes planus may help guide more targeted and effective treatment strategies.

Purpose:

The aim of this multicenter cross-sectional study was to determine the prevalence of central sensitization and nociplastic pain in individuals with clinically diagnosed pes planus and to compare the findings with age- and sex-matched healthy controls.

Methods:

Between November 2024 and May 2025, a total of 107 patients with pes planus and 107 healthy controls were recruited from three medical centers. Participants completed validated Turkish versions of the Visual Analog Scale for pain intensity, the Foot Function Index for functional limitation, the Pain-DETECT questionnaire for nociplastic pain symptoms, the Central Sensitization Inventory for central sensitization, the Hospital Anxiety and Depression Scale for psychological distress, and the Short Form-12 for quality of life. Data were analyzed using comparative statistical tests and multiple linear regression models to identify factors associated with nociplastic pain and central sensitization in the pes planus group.

Pes planus, also referred to as flatfoot, is a common musculoskeletal condition characterized by the flattening or collapse of the medial longitudinal arch of the foot. It affects a considerable portion of the adult population and may be associated with foot pain, functional impairment, and reduced quality of life. In many patients, pain symptoms persist despite adequate structural correction and conventional treatments such as footwear modifications, orthotic support, exercise, or anti-inflammatory medications. This persistence suggests that central mechanisms of pain processing may be involved.

Central sensitization is a phenomenon in which the central nervous system exhibits heightened responsiveness to sensory input, resulting in amplified pain perception even in the absence of ongoing tissue injury. Nociplastic pain is a relatively new classification describing pain arising from altered central nociceptive processing without clear evidence of tissue damage or nerve injury. Both mechanisms are increasingly recognized in chronic musculoskeletal disorders, yet they have been underexplored in individuals with pes planus.

This multicenter cross-sectional study was designed to investigate the prevalence of central sensitization and nociplastic pain in adults with clinically diagnosed pes planus and to compare these findings with healthy controls matched for age and sex. Participants were recruited from three medical centers between November 2024 and May 2025. Inclusion criteria required adults aged 18 to 65 years with lower extremity pain lasting at least six months and a diagnosis of pes planus confirmed by a physical medicine and rehabilitation specialist. Healthy controls had no history of foot or leg pain or relevant musculoskeletal disorders.

All participants completed standardized and validated assessment tools, including the Visual Analog Scale for pain intensity, the Foot Function Index for foot-related disability, the Pain-DETECT questionnaire for nociplastic pain features, the Central Sensitization Inventory for signs of central sensitization, the Hospital Anxiety and Depression Scale for psychological distress, and the Short Form-12 for quality of life. Demographic and clinical information was also recorded.

Statistical analyses compared results between the pes planus and control groups and examined correlations among pain severity, functional impairment, central sensitization, nociplastic pain, and psychological measures. Multiple linear regression models were used to identify independent predictors of nociplastic pain and central sensitization in the pes planus group.

The findings of this study are intended to improve understanding of the complex pain mechanisms associated with pes planus and to highlight the potential need for multidisciplinary management approaches that address central pain processes and psychological factors alongside conventional biomechanical interventions.

Inclusion Criteria:

• Age between 18 and 65 years.
• For pes planus group: clinically diagnosed pes planus confirmed by physical medicine and rehabilitation specialists, with persistent lower extremity pain for at least 6 months.
• For control group: age- and sex-matched healthy volunteers without current or past foot or leg pain.
• Willingness to complete all self-report questionnaires.
• Provided written and verbal informed consent.

Exclusion Criteria:

• History of diabetes mellitus, hypothyroidism, malignancy, vasculitis, neuropathies, or lumbar radiculopathy.
• History of lower limb surgery or trauma.
• Recent local injection or extracorporeal shockwave therapy.
• Any rheumatologic disease affecting pain perception (e.g., rheumatoid arthritis, ankylosing spondylitis).
• Severe psychiatric disorder or cognitive impairment interfering with questionnaire completion.

Adults aged 18-65 years, including individuals with clinically diagnosed pes planus and age- and sex-matched healthy volunteers without lower extremity pain. Participants were recruited from physical medicine and rehabilitation clinics at Etlik Zübeyde Hanım Gynecology and Pediatrics Training and Research Hospital, Ankara Etlik City Hospital, and Yozgat City Hospital.

Individual participant data that underlie the results reported in the article (after deidentification) will be made available upon reasonable request to the corresponding author after publication. Data will be shared with researchers who provide a methodologically sound proposal for use in achieving the aims stated in their proposal. Requests should be directed to gulserendmr58@hotmail.com. Data will be available for 12 months following article publication.

De-identified individual participant data and supporting materials will be available beginning 6 months after publication of the main study results and will be accessible for a period of 12 months thereafter.

Data will be available to qualified researchers with a methodologically sound proposal for secondary analyses related to the study objectives. Requests should be submitted to the corresponding author at gulserendmr58@hotmail.com. Approved requestors will be provided access via secure email or institutional file transfer systems.