How does the arch detector (plantar 3D scanner) measure flatfoot and high arch?

I. Basic Principle

The arch detector mainly evaluates the condition of the arch through plantar three-dimensional shape scanning + arch index calculation + (optional) dynamic pressure detection.

• Three-dimensional scanning: Using laser/infrared/structured light to collect the three-dimensional shape of the plantar surface, obtaining parameters such as arch height, foot length, and foot width.

• Index calculation: Based on the scanning parameters, calculate several commonly used clinical indicators (such as AHI, CSI, SI) to determine the arch type.

• Dynamic detection (in some devices): Combined with a pressure plate, analyzing the stretching and contraction of the arch during the gait cycle.

II. Common Indicators and Their Significance

Arch Height Index (AHI)

• Lower → Flatfoot

• Normal range → Normal arch

• Higher → High arch

• Formula: Arch height ÷ Foot length

• Judgment:
  

Chippaux-Smirak Index (CSI)

• 45% → Flatfoot

• 25%–45% → Normal arch

• <25% → High arch

• Formula: Narrowest width of midfoot ÷ Maximum width of forefoot × 100%

• Judgment:

Staheli Index (SI)

• 1.15 → Flatfoot

• 0.89–1.15 → Normal arch

• <0.89 → High arch

• Formula: Midfoot width ÷ Heel width

• Judgment:

III. Detection Process

Static detection

• The subject stands on the scanning platform, maintaining a natural upright posture.

• The scanner collects three-dimensional plantar data and automatically generates a foot shape model.

• The software extracts arch height, arch curvature, and various indices.

Dynamic detection (optional)

• The subject walks naturally on a gait platform equipped with pressure sensors.

• The device collects plantar pressure distribution and arch deformation during the gait cycle.

• Analyze whether there is hidden flatfoot (normal in static condition, but arch collapse during dynamic condition).

IV. Detection Characteristics of Flatfoot and High Arch

Flatfoot

• Arch height significantly decreased, AHI low;

• CSI and SI significantly increased (the midfoot bearing area widened);

• In dynamic detection, arch collapse during the gait cycle is more obvious, often accompanied by foot pronation.

High arch

• Arch height significantly increased, AHI high;

• CSI and SI values decreased (the midfoot contact area is narrow);

• In dynamic detection, arch elasticity is insufficient, shock absorption is poor, and pressure is concentrated on the forefoot and heel.