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Longitudinal Arch Angle

Postural assessment tools are designed to be clinically practical tools for measuring foot posture in an attempt to relate that static measurement to dynamic function or potentially predict future degradation or injury of the foot.

The Functional Foot Typing (FFT) System [1][]

A system used to classify a foot into one of 16 categories, with that classification then determining casting, modification, and fabrication approach.

The System is Based on SERM-PERM Testing and the SERM-PEM Interval.

The 16 categories compare forefoot range of motion to rearfoot range of motion and are as follows with the highlighted ones being the most common (see Illustration):

  1. Rigid/Rigid
  2. Rigid/Stable
  3. Rigid/Flexible
  4. Rigid/Flat
  5. Stable/Rigid
  6. Stable/Stable
  7. Stable/Flexible
  8. Stable/Flat
  9. Flexible/Rigid
  10. Flexible/Stable
  11. Flexible/Flexible
  12. Flexible/Flat
  13. Flat/Rigid
  14. Flat/Stable
  15. Flat/Flexible
  16. Flat/Flat

How To Measure:[]

Supinatory End Range Motion (SERM) and Pronatory End Range Motion (PERM) must be tested at the forefoot and rearfoot.

  • Rigid rearfoot- inverted subtalar SERM, inverted subtalar PERM
  • Stable rearfoot- inverted subtalar SERM, perpendicular subtalar PERM
  • Flexible rearfoot- inverted subtalar SERM, everted subtalar PERM
  • Flat rearfoot- everted subtalar SERM, everted subtalar PERM
  • Rigid forefoot- forefoot SERM 1st metatarsal below 5th, PERM 1st metatarsal below 5th
  • Stable forefoot- forefoot SERM 1st metatarsal below 5th, PERM 1st metatarsal in line with 5th
  • Flexible forefoot- forefoot SERM 1st metatarsal below 5th, PERM 1st metatarsal above 5th
  • Flat forefoot- forefoot SERM 1st metatarsal above 5th, PERM 1st metatarsal above 5th

Clinically, almost all feet (95%+) can be successfully foot typed one of The 5 Common Foot Types:

The 5 Common Foot Types

The Longitudinal Arch Angle (LAA)[]

The angle formed by two lines found on a static foot and used to predict dynamic foot function and posture. The LAA has been found to accurately predict foot posture as well as regional plantar pressures in the stance phase of gait.

How To Measure:[]

To find the LAA, have the patient stand in a relaxed position with the foot to be measured maximally internally rotated. Simply palpate and mark as necessary to find three points, making two lines, making one angle: 

  1. A line passing through the midpoint of the medial malleolus to the navicular tuberosity
  2. A line passing through the midpoint of the medial aspect of the first metatarsal head to the navicular tuberosity.

The Foot Posture Index (FPI)[]

A diagnostic clinical tool aimed at quantifying the degree to which a foot can be considered to be in a pronated, supinated, or neutral position. It is a method for scoring various features of foot posture into a single quantifiable result, which in turn gives an idea of overall foot posture. [2]

How To Measure:

With the patient in a relaxed static position of double limb support, you will grade their foot posture using the following criteria:

  1. Talar head palpation
  2. Curves above and below the medial malleoli
  3. Inversion/eversion of the calcaneus
  4. Bulge in the region of the talonavicular joint
  5. Congruence in the medial longitudinal arch
  6. Adduction/abduction of the forefoot on the rearfoot

Each criterion is graded between -2 for obvious supination and +2 for obvious pronation. The sum total of all scores will either be significantly positive for overall pronation, negative for overall supination, or around zero for neutral.

The Foot Line Test (FLT)[]

The FLT is a the measurement of the prominence of the navicular in a mediolateral direction in an attempt to describe the amount of pronation and therefore predict and prevent potential overuse injuries which can result from excessive pronating.

How To Measure:[]

Place a piece of paper under the foot to be measured. Project the medial border of the foot onto the paper with a writing utensil. You will have to use a special device to keep the utensil perfectly perpendicular to the paper. Palpate the 1st MTPJ and navicular tuberosity and mark each apex on the medial border line. Mark two projection points on the medial border line; one 3cm posterior to the first MTPJ and one 5 cm posterior to the navicular. Connect these two projection points to create a static reference line. The distance between the static reference line and the medial border line at the point of the navicular tuberosity is measured in millimeters. Note a positive value if the medial border line is medial to the static reference line and vice versa. [3]

The Arch Index[]

A method of measuring static footprints for the purpose of determining high, normal, and flat arch types.

How To Measure:[]

With the patient standing in a static, 50% body weight per limb, position you must capture the footprint. You will then find the ratio of the area of the middle third of the footprint to the area of the entire footprint (excluding the toes) in order to determine a high, normal, or flat arch type.

The Malleolar Valgus Index (MVI)[]

A static measurement used to help categorize a foot structure as either planus, rectus, or cavus. [4]

How To Measure:[]

This measurement most commonly requires a flatbed scanner as well as a special malleolar jig. Once a scan of the foot is obtained, multiple lines are transcribed upon it.

  • A medial border line, tangential to the most medial points of the 1st metatarsal head and the heel
  • A lateral border line, tangential to the most lateral points of the 5th metatarsal head and the heel
  • A foot bisection line
  • An anterior line crossing the medial and lateral border lines, perpendicular to the medial border line and tangential to the anterior most point of the longest toe
  • A posterior line, crossing the medial and lateral border lines, perpendicular to the medial border line and tangential to the posterior most point of the heel
  • An ML line crossing through the midpoint of each malleolus

Use the following formula to arrive at the MVI value:


ML=the length between the outer most point of each malleolus on the ML line

BC=the length between the foot bisection line and the midpoint of the ML line

MVI planus > 20

MVI cavus < -20

The Arch Height Index (AHI)[]

A measurement system for determining the height of a patient's dorsum reliably and repeatably for later use in classification of foot type or potential prediction and treatment of pathology.

How To Measure:[]

AHI should be measured twice for each foot to be measured. Once while sitting (each limb supporting 10% body weight) and once standing comfortably under double limb support (each limb supporting 50% body weight). Supination or pronation could easily skew results, so maintain a neutral rearfoot and forefoot throughout the measurements. Measure the height to the top of the dorsum at 1/2 the total foot length from the heel. To compare arch height between patients of different size, arch height measurements can be normalized by the truncated foot length to give the actual Arch Height Index. [5]