The human foot is a complex structure designed to absorb shock and propel the body, making its alignment a significant factor in overall body mechanics. Assessing foot posture is a standardized step in biomechanical evaluations, providing objective data on how the foot is positioned during standing. The Foot Posture Index (FPI) is a standardized, reliable clinical tool developed to quantify this static foot posture. This article explains the components of the FPI, details how it is measured, and outlines how the resulting scores are used by health professionals.
Defining the Foot Posture Index
The Foot Posture Index (FPI) is a validated, multi-item assessment tool designed to systematically measure the position of the foot in a standing, weight-bearing position. It moves beyond simple visual estimation by providing a structured method for scoring various aspects of foot alignment. The tool focuses on classifying the foot into distinct categories: supinated, neutral, or pronated. This classification is achieved by totaling the scores from six individual observational criteria. The FPI yields a single numerical score that can range from -12 to +12. Negative scores indicate a foot tending toward supination, while positive scores suggest a foot tending toward pronation.
The Six Measurement Components
The FPI is calculated by a clinician observing and manually assessing six specific features of the foot and assigning a score for each, ranging from -2 to +2.
The first observation assesses the position of the head of the talus, a bone located in the ankle, to determine if it is prominently bulging on the inside or outside of the foot. Next, the clinician examines the supra- and infra-malleolar curvature, noting the shape of the soft tissue curves located above and below the ankle bone (malleolus) on the outside of the ankle.
The third component is the calcaneal position, which is the angle of the heel bone (calcaneus) in the frontal plane, looking for outward tilting (eversion) or inward tilting (inversion). The fourth criterion is the prominence of the talonavicular joint, observing for a visible bulge on the inner side of the foot which indicates a collapse of the arch structure.
The fifth observation evaluates the medial longitudinal arch congruence, determining the height and shape of the arch and how much of its structure is in contact with the ground. Finally, the sixth component involves observing the forefoot on the rearfoot, specifically looking for abduction (toes pointing outward) or adduction (toes pointing inward) while the patient stands. Each of these six observations is scored on a five-point scale, where a score of zero represents a neutral position, negative values are given for supination, and positive values are given for pronation.
Interpreting the Final Score
The final FPI score is determined by summing the scores from the six observational components, resulting in a single value between -12 and +12. A score of zero represents a perfectly neutral, non-deviated foot posture, though few individuals exhibit this exact alignment. Most healthy individuals fall within a slightly pronated range, with scores between 0 and +5 typically being considered a neutral or normal foot type.
Scores that fall into the range of +6 to +12 are generally classified as pronated, or flat, feet, with the higher numbers indicating a progressively flatter posture. Conversely, scores that are negative suggest a supinated, or high-arched, foot type. For instance, a score between -5 and -12 is commonly classified as a highly supinated foot, reflecting a rigid, highly arched structure. These numerical classifications allow clinicians to objectively categorize a patient’s foot type based on a standardized and repeatable metric.
The Role of FPI in Musculoskeletal Health
Quantifying foot posture with the FPI provides an important link between foot structure and potential musculoskeletal health issues. Variations in foot alignment, especially highly supinated or highly pronated postures, can alter the body’s mechanics, affecting the joints and soft tissues higher up the kinetic chain. Research suggests that an extreme FPI score may be related to an increased likelihood of certain common lower extremity injuries.
For example, excessive foot pronation may contribute to conditions like plantar fasciitis or Achilles tendinopathy, while a highly supinated foot might be associated with stress fractures due to reduced shock absorption. This objective data helps clinicians identify individuals who may be at a higher risk of developing pain in the ankles, knees, hips, or lower back. The FPI score is then used to guide treatment, informing decisions regarding the prescription of custom foot orthotics, specific footwear recommendations, or the design of targeted strengthening and stretching exercise programs.