Posted by on Jul 30, 2013 in Biomechanics | 0 comments

 

What Foot Type Is This?

 sagittal frotal comparrison

Both pictures above are of the same right foot, in the same position but taken from different angles.  The pictures were taken with the person in a relaxed stance.  The picture on the left is a sagittal plane picture of the medial aspect of the foot, the picture on the right is frontal plane picture of the rear foot.

 

Many websites, running magazines and running shops talk of foot types, so my question is; what foot type is this?

 

What do the pictures show?

The pictures below were taken with the person stood in a relaxed posture.  The picture on the left clearly shows a medial arch, typical of a neutral and cavus foot type (cavus aka high arched, under pronated and supinated foot). The picture on the right shows further signs of a neutral or cavus foot type; the back of the heel bone being less than 5° from vertical (not shown clearly in the picture), the area under the medial malleolus (ankle bone) is concave in shape and the lateral edge of the foot is relatively straight.

sagittal frontal bisection

If this person were to carry out a wet-foot test or a running shop gait analysis they would find a high arch with a low to normal range of pronation and be classed as having a high arched, under pronating, supinated foot type.  Then be advised to buy neutral or cushioned trainers.

 

If we look at the movement that the foot goes through and the entire lower limb we get a different answer.

 

RF frontal comparrison

 

The above picture shows the same right foot in subtalar joint neutral (left) and in relaxed stance (right).  Comparing the positions it is clear that the foot is moving through its full range of pronation.  The magazines, websites and running shops say a pronated foot = low or no arch.  Yet this foot is pronated and has a clear, obvious arch.  How can this be?  Looking at the picture below you will see this person has varus tibias (bow legged).  The black line shows where the tibia is, the red line indicates where the tibia would be if the person had textbook legs.

 

frontal feet together marked

 

This causes the rear foot to contact the ground at a greater angle than usual.  Therefore the foot must pronate to its fullest extent to get the big toe to the ground, giving the illusion of a foot that does not pronate enough.

It is important to note that tibial varus is normal and not fault or deformity.  It does not increase the risk of injury but it does change the type of injury a person is likely to get e.g. people with tibia varus are likely to suffer ankle sprains but are unlikely to suffer medial tibial stress syndrome (shin splints).  Different injuries will occur because the impact forces generated during walking/running will stress tissues differently in a person with varus tibias compared to a person with normal tibias.

If this person were to present at a sports injury clinic the clinician must identify the injured tissue then identify and reduce the force that has caused the tissue to become injured.

The moral of the story is not to think about and treat foot types but treat the forces that cause injury.

Further reading:

How Do Biomechanical Injuries Occur

Pronation Supination, Whats That All About

Books about biomechanics and gait analysis