Foot Posture Index is a composite measure of the posture of the foot based on 6 different observations of the alignment or posture of different segments of the foot.

The Foot Posture Index (FPI) is a widely used clinical tool for quantifying standing foot posture, helping to classify feet as pronated, neutral, or supinated. The most common version is the FPI-6, which involves observing and scoring six specific criteria. This assessment is quick, simple, and reliable, making it valuable for clinicians and researchers alike.

Here’s how to calculate the FPI-6:

1. Preparation and Patient Positioning
The patient should stand barefoot in a relaxed, neutral stance with both feet supporting their weight. Their arms should be naturally at their sides, and they should look straight ahead. It can be helpful to have them march in place for a few steps before settling into their stance. The assessment usually takes about two minutes, and the assessor needs to be able to move around the patient freely.

2. The Six Criteria and Scoring
Each of the six criteria is scored on a 5-point scale, ranging from -2 to +2. A score of 0 indicates a neutral position for that specific criterion. Positive values (+1, +2) are given for pronated features, with higher scores indicating more pronation. Negative values (-1, -2) are given for supinated features, with more negative scores indicating more supination. If an observation cannot be made (e.g., due to swelling), it should be skipped and noted.

The six criteria are:

• Talar Head Palpation (Transverse Plane): This involves palpating the talar head. The score depends on whether the talar head is more palpable on the lateral (outer) or medial (inner) side of the foot.
• Curves Above and Below the Lateral Malleolus (Frontal/Transverse Plane): Observe the curvature around the ankle bone (lateral malleolus) from behind. The score is based on whether the curve below the malleolus is straight, convex, or more or less concave compared to the curve above it.
• Calcaneal Frontal Plane Position (Frontal Plane): Observe the heel bone (calcaneus) from behind. The score reflects whether the heel is inverted (varus), everted (valgus), or vertical, often estimated in degrees.
• Prominence in the Region of the Talonavicular Joint (Transverse Plane): View the inside of the foot at an angle. The score depends on whether this area is concave, flat, or bulging.
• Congruence of the Medial Longitudinal Arch (Sagittal Plane): Observe the inner arch of the foot from the inside. The score ranges from a high, acutely angled arch to a very low, flattened arch that might be making ground contact.
• Abduction/Adduction of the Forefoot on the Rearfoot (Transverse Plane): View the foot from behind. The score is based on how many medial (inner) or lateral (outer) toes are visible, indicating whether the forefoot is abducted (splayed out) or adducted (turned in) relative to the rearfoot.

3. Total Score and Classification
After scoring each of the six items, sum the individual scores to get a total FPI-6 score. The total score can range from -12 (severely supinated) to +12 (severely pronated). The foot posture is then classified based on this total score:

• Severely Supinated: ≤ -5
• Mildly Supinated: -1 to -4
• Neutral Posture: 0 to +5
• Mildly Pronated: +6 to +9
• Severely Pronated: ≥ +10

It’s important to note that a slightly pronated foot posture (mean raw score of +4) is considered the normal position at rest in a healthy adult population. The FPI is a practical tool that aids in deciding appropriate interventions, such as strengthening exercises, stretching, manual therapy, gait training, or selecting suitable orthotics.

Most Useful Resources:
Foot Posture Index (Podiatry TV)
The Foot Posture Index (Podiatry Update)
Foot Posture Index (Clinical Boot Camp)
Foot Posture Index (PodiaPaedia)
Foot Posture Index (Podiatry Arena)