|Normal foot function
Normal foot function is represented by a natural cycle of pronation and supination, accompanied by internal and external rotation of the lower leg (see diagrams above). Abnormal foot function is commonly associated with Excess Pronation. At contact phase the lower limb approaches the ground with a slight angle of 3-4 degrees. This natural strike angle is referred to as the ‘Tibial Varum Angle’. As a result, the foot strikes on the outside of the calcaneus (heel bone). Next, the foot’s bone and muscle structures loosen and the foot pronates at the Subtalar Joint. This is our natural shock absorbing mechanism and it allows our feet to adapt to whatever surface we walk on.
During midstance the foot converts from mobile adaptor into a rigid lever, preparing for propulsion (supination). As the foot supinates the lower leg starts to rotate externally.
The problem occurring in many people is that during midstance the foot continues to pronate and remain loose, not allowing the foot to supinate (roll outwards) and become rigid in preparation for the propulsive phase.
Excess Pronation is very common, affecting at least half of the population. It can be attributed to different factors, including the hard, unnatural surfaces we walk on, unsupportive footwear, weak or fatigued muscles, age, body weight, arthritis, genetic factors etc.
The photos to the right show the right foot in neutral stance (Subtalar Joint in neutral, during midstance phase), as well as pronated excessively. Please take note of how the medial maleolus (inside ankle bone) is clearly protruded with excess pronation, and longitudinal arch is lowered significantly. Excess pronation commonly exhibits:
• Calcaneal eversion
• Internal tibial rotation
• Lowering and elongation of the longitudinal arch
• Excess medial lower limb stress
• Medial plantar displacement of the talus upon the calcaneus
• Excess weight bearing over the 1st metatarso-phalangeal joint
NOTE: Practitioners will often examine the patient's shoe wear at the sole of the shoe, aiding in the assessment of foot biomechanics. Because the foot always lands on the outside of the heel first, most people’s footwear will wear out faster on the outside heel of the shoe. This uneven wear of the shoesole is often misinterpreted as a sign of over-supination (i.e. walking on the outside of the feet). Shoe wear on the outside sole is common for both supinators and pronators as both groups always land on the outside of the foot first.