The Foot Posture Index

The human foot is a biomechanical marvel – a complex structure of 26 bones, 33
joints, and over 100 muscles, tendons, and ligaments that collectively bear the
entire weight of the body while facilitating locomotion. Given this complexity,
clinicians and researchers have long sought reliable, practical tools to assess foot
posture and identify deviations that may contribute to pain, dysfunction, or
injury. One such tool is the Foot Posture Index (FPI), a validated clinical
instrument designed to quantify foot posture in a simple, reproducible, and
clinically meaningful way. Since its development, the FPI has become one of the
most widely used and studied methods of foot assessment in both clinical and
research settings.

Origins and Development
The Foot Posture Index was developed by Anthony Redmond and colleagues in
the early 2000s as a response to the limitations of existing foot assessment
methods. Prior to its introduction, clinicians relied on a range of measures –
including static arch height, navicular drop, and radiographic measurements –
each of which carried its own drawbacks in terms of reliability, clinical
applicability, or time requirements. The FPI was designed to be a fast,
non-invasive, and observer-friendly tool that could be applied in routine clinical
practice without specialist equipment.
The original FPI comprised eight criteria, later refined into six in the more widely
adopted FPI-6 version. The FPI-6 is now the standard form used in research and
clinical environments worldwide. It was validated against radiographic measures
of foot posture, and studies have demonstrated its acceptable inter- and
intra-rater reliability, making it a robust instrument for both clinical
decision-making and epidemiological research.

The Six Criteria of the FPI-6
The FPI-6 assesses the foot across six discrete clinical observations, each scored
on a five-point scale ranging from -2 to +2. A score of 0 represents a neutrally aligned foot, negative scores indicate supination (a more underpronated or
high-arched foot), and positive scores indicate pronation (a flatter, more rolled-in
foot).
1. Talar Head Palpation: The clinician palpates the head of the talus on both the
medial and lateral aspects of the foot. In a pronated foot, the medial aspect will be
more prominent and convex, while the lateral aspect will feel concave.
2. Supra and Infra Lateral Malleolar Curvature: The curvature above and below
the lateral malleolus is assessed. In a neutrally aligned foot, both curves are
roughly equal. Pronation produces a more pronounced infra-malleolar curvature.
3. Calcaneal Frontal Plane Position: The posterior surface of the calcaneus is
observed for varus (inverted) or valgus (everted) positioning. A vertical calcaneus
scores 0; valgus deviation scores positively; varus deviation scores negatively.
4. Bulging in the Region of the Talonavicular Joint: The clinician observes
whether the skin over the talonavicular joint bulges medially, reflecting
pronatory displacement of the navicular bone. A flat profile is neutral; bulging
scores positively.
5. Congruence of the Medial Longitudinal Arch: The height and shape of the
medial longitudinal arch are observed. A well-defined, curved arch is neutral; a
flattened arch scores positively; an accentuated, high arch scores negatively.
6. Abduction/Adduction of the Forefoot on the Rearfoot: The assessor views the
foot from behind to determine whether more of the forefoot is visible on the
lateral side (pronation/abduction) or on the medial side (supination/adduction).
The individual scores are summed to produce a total FPI score. The normative
range for adults is generally +0 to +5, indicating a mildly pronated foot consistent
with normal bipedal gait. Scores of +6 to +9 suggest a pronated foot, while +10 and
above indicates a highly pronated foot. Negative scores indicate varying degrees
of supination.

Clinical Significance and Applications
The FPI has found broad application across multiple domains of musculoskeletal
health. Foot posture is intimately connected to the biomechanics of the lower
limb and has been implicated in a variety of clinical conditions. Excessive
pronation, as measured by a high FPI score, has been associated with plantar
fasciitis, patellofemoral pain syndrome, medial tibial stress syndrome (shin
splints), posterior tibial tendon dysfunction, and hallux valgus. Conversely, highly supinated foot posture has been linked to lateral ankle sprains, stress fractures,
and iliotibial band syndrome.
By providing a standardised quantification of foot posture, the FPI enables
clinicians to identify at-risk patients, monitor changes over time following
intervention, and conduct meaningful comparisons across populations. In
physiotherapy and podiatry practice, the FPI informs the prescription of orthotic
devices, footwear recommendations, exercise programs, and manual therapy
approaches.
In sports medicine, the FPI has been particularly valuable in injury risk profiling.
Research has explored associations between FPI scores and lower-limb injury
rates in athletic populations, informing pre-participation screening programs.
Similarly, in paediatric health, population-level FPI data has helped establish
normative foot posture values for children at different stages of development,
recognising that a degree of pronation is normal in young children and typically
resolves with age.

Limitations
Despite its strengths, the FPI-6 is not without limitations. As a clinical observation
tool, it relies on the visual and tactile acuity of the assessor, and training is
required to achieve acceptable reliability. Some studies have reported only
moderate inter-rater reliability, particularly among less experienced clinicians.
Additionally, the FPI captures a static, bilateral weight-bearing snapshot of foot
posture, which may not fully reflect dynamic foot function during walking or
running – contexts in which many foot-related pathologies actually manifest.
Furthermore, the FPI assesses posture rather than function, and a high or low
score does not necessarily indicate pathology. Many individuals with significantly
pronated or supinated feet remain entirely asymptomatic. The index must
therefore be interpreted within the broader clinical context, alongside gait
analysis, strength assessment, and patient history.

The Foot Posture Index represents a significant contribution to clinical
biomechanics and musculoskeletal assessment. Its standardised six-criterion
framework, ease of application, and growing body of normative and clinical data
make it an indispensable tool for clinicians working with foot and lower-limb
conditions. While it has inherent limitations as a static, observational measure, its
value lies in providing a common clinical language for foot posture – one that bridges research and practice, and ultimately supports better, more informed care
for patients with foot-related complaints. As our understanding of foot
biomechanics continues to evolve, the FPI remains a cornerstone of
evidence-based lower-limb assessment.