The Use of the Foot Posture Index in Clinical and Research Settings

The Foot Posture Index (FPI), particularly its refined six-item version known as FPI-6, represents a significant advancement in the assessment of foot biomechanics. Developed as a clinical tool to quantify standing foot posture, the FPI-6 allows healthcare professionals to classify feet along a continuum from highly supinated to highly pronated. This classification is crucial because abnormal foot postures, such as excessive pronation or supination, are linked to various musculoskeletal issues, including lower limb injuries, chronic pain, and gait abnormalities. Unlike traditional methods that often rely on subjective observations or complex equipment, the FPI-6 offers a standardized, objective approach that can be performed quickly in everyday clinical environments. Its primary purpose is to serve as a diagnostic aid, helping practitioners identify deviations from neutral foot alignment and tailor interventions accordingly. For instance, in podiatry, physiotherapy, and orthopedics, the FPI-6 informs decisions on orthotic prescriptions, exercise programs, and surgical considerations. Moreover, its application extends to research, where it facilitates the study of foot-related pathologies in diverse populations, from athletes to the elderly. By providing a reliable metric, the FPI-6 bridges the gap between static assessment and functional implications, though it is not without limitations. This essay explores the methodology, applications, advantages, and constraints of the FPI-6, highlighting its role in modern healthcare.

The origins of the Foot Posture Index trace back to the early 2000s, driven by the need for a more comprehensive and user-friendly alternative to existing foot assessment techniques. In 2006, researchers led by Anthony Redmond developed and validated the FPI through a multi-phase process detailed in a seminal study published in *Clinical Biomechanics*. The development began with a thorough literature review, identifying 36 potential clinical measures of foot posture from over 100 papers. These were categorized into direct, indirect, and supplementary tests, among others. Candidate components were then refined based on validity, reliability, and practicality. Initially, an eight-item draft was tested, but factor analysis and inter-item reliability assessments (with Cronbach’s α = 0.83) led to the elimination of redundant or less predictive elements, resulting in the streamlined FPI-6. Validation involved comparing the tool against established measures like Rose’s Valgus Index and three-dimensional kinematic models using electromagnetic motion tracking. The FPI-6 demonstrated strong predictive validity, accounting for 64% of variance in static posture and 41% in midstance during walking. This rigorous process ensured the tool's robustness, making it suitable for both experienced and novice clinicians. Since its inception, the FPI-6 has been adopted globally, with ongoing studies affirming its utility while refining its application.

At the heart of the FPI-6 is its straightforward methodology, which emphasizes observational and palpatory techniques without requiring specialized equipment. The assessment begins with patient positioning: the individual stands in a relaxed, double-limb support stance, arms at their sides, gazing forward. To achieve a natural posture, the patient may march in place briefly before settling, allowing the assessor approximately two minutes to evaluate both feet from various angles—primarily posterior, medial, and angled views. The tool comprises six specific criteria, each scored on a five-point scale from -2 (indicating supination features) to +2 (indicating pronation features), with 0 representing neutral alignment.

The first criterion involves palpation of the talar head at the navicular tuberosity. A score of -2 is given if the talar head is palpable only on the lateral side (supinated), escalating to +2 if palpable only medially (pronated). Next, the curvature above and below the lateral malleoli is observed from behind: -2 for a convex or straight lower curve (supinated), and +2 for a markedly more concave lower curve (pronated). The third item assesses calcaneal position in the frontal plane, also from the rear: -2 for inversion greater than 5 degrees (varus), +2 for eversion exceeding 5 degrees (valgus). Moving to the medial view, the fourth criterion evaluates prominence at the talonavicular joint: -2 for a concave area, +2 for significant bulging. The fifth examines the medial longitudinal arch's height and congruence: -2 for a high, acutely angled arch, +2 for a severely flattened arch contacting the ground. Finally, forefoot abduction or adduction relative to the rearfoot is judged from behind: -2 if more medial toes are visible (adducted/supinated), +2 if more lateral toes are seen (abducted/pronated).

Scoring is additive, yielding a total FPI-6 score ranging from -12 (highly supinated) to +12 (highly pronated). Interpretation categorizes feet as follows: +10 to +12 highly pronated, +6 to +9 pronated, 0 to +5 neutral, -1 to -4 supinated, and -5 to -12 highly supinated. This system allows for bilateral comparisons and tracking changes over time, such as pre- and post-intervention. Tips for accuracy include consistent palpation pressure, avoiding patient tension, and focusing on subtle asymmetries, as outlined in quick reference guides.

The applications of the FPI-6 are broad, spanning clinical practice and research. In clinical settings, it aids in diagnosing conditions like pes planus (flat feet) or pes cavus (high arches), which can contribute to plantar fasciitis, shin splints, or knee osteoarthritis. For example, a pronated foot (positive score) might prompt strengthening exercises for intrinsic muscles or custom orthotics to redistribute pressure. In sports medicine, the FPI-6 screens athletes for injury risk; studies have linked pronated postures to increased incidence of lower extremity overuse injuries in runners. It also supports multidisciplinary care, such as in diabetes management, where it identifies biomechanical risks for neuropathic ulcers. In research, the FPI-6 enables standardized classification of participants, facilitating investigations into age-related foot changes, falls prevention in older adults, and the efficacy of interventions like footwear modifications. Its use in pediatric populations, as evidenced by reliable assessments in children with low back pain, underscores its versatility. Furthermore, the tool has been employed in epidemiological studies to explore correlations between foot posture and systemic conditions, enhancing evidence-based practice.

One of the primary advantages of the FPI-6 is its efficiency and accessibility. Requiring no tools beyond the clinician's hands and eyes, it can be completed in minutes, making it ideal for busy clinics. Its multi-segment, multi-plane evaluation captures a holistic view of foot alignment, surpassing single-plane goniometric measures in validity. Reliability is another strength: inter-rater agreement is excellent (ICC 0.85-0.97), even among inexperienced examiners like students, with Kappa values around 0.72-0.73 for classification. This democratizes its use, reducing dependency on expert practitioners. Additionally, its quantitative output supports objective tracking and research comparability.

Despite these benefits, the The Foot Posture Index-6e has notable limitations. As a static assessment, it poorly correlates with dynamic foot function during activities like walking. A cross-sectional study of 100 adults found weak associations between FPI scores and baropodometric parameters such as contact area, force, and pressure, with correlations often below 0.3. This implies the tool cannot predict gait mechanics or distinguish between rigid and flexible deformities, potentially leading to incomplete clinical pictures. Challenges also arise in cases of swelling or anatomical variations, where certain criteria may be unscoreable. While reliable overall, specific items like malleolar curvature require targeted training to minimize variability. Critics argue it should complement, not replace, dynamic analyses like gait studies for comprehensive evaluations.

The Foot Posture Index-6 is a valuable tool that enhances foot assessment through its simplicity, reliability, and broad applicability. By quantifying posture, it empowers clinicians and researchers to address biomechanical issues effectively. However, acknowledging its static nature and integrating it with dynamic methods ensures optimal outcomes. As foot health gains prominence in preventive care, the FPI-6 will likely evolve, solidifying its place in evidence-based practice.

Craig Payne is a University lecturer, runner, cynic, researcher, skeptic, forum admin, woo basher, clinician, rabble-rouser, blogger and a dad.