column in 1999 . 5 The authors placed sensors on each of the bones of the medial column of the foot ( 1st metatarsal , 1 st cuneiform , navicular , and talus ) recording the movement of each bone with increasing loads applied the Achilles tendon . 5 The normal role of the Peroneus Longus tendon to evert the medial column of the foot into the central column of the foot was dampened . 5 This dampening effect led to the unlocking of the midtarsal joint and hypermobility with the arch flattening at the naviculocuneiform joint . 5 The first metatarsal and first cuneiform dorsiflexed and the navicular and talus plantarflexed . 5 This explains why frequently on lateral x-ray views there is a navicular-cuneiform sag .
Amis examined the effect of equinus dynamically during gait . 6 Using video at 250 frames per second ( FPS ), Amis demonstrated the exact time sequence during the gait cycle when the destructive leveraged forces occur on foot .
Amis termed this the “ split second effect .” 6 The pathological force created last for approximately 1 / 200 ms ( 1 / 10 second ). 6 The split-second effect occurs during the last half of midstance when the swing phase foot pass starts to pass the planted foot before heel lift on the planted foot . 6 This fourth rocker at the naviculocuneiform joint is the active version of Johnson and Christensen findings .
With the information provided by the three previously mention studies , it becomes evident why functional orthoses and an equinus deformity are adversaries . The orthoses are supporting the medial column of the foot with the medial flange and posting if present . The Gastocsoleal complex is driving the arch downward at the naviculocuneiform joint . These two forces are opposing each , with the result being arch irritation or a feeling of the medial arch being too high .
Figure 3 — Incorrect sagittal plane position of the foot in pronation to evaluate ankle joint dorsiflexion unlocking the midtarsal joints and pronating the hindfoot position allowing dorsiflexion to occur in the midfoot
Figure 4 — Incorrect frontal plane position of the foot in pronation to evaluate ankle joint dorsiflexion unlocking the midtarsal joints and pronating the hindfoot position allowing dorsiflexion to occur in the midfoot