This article discusses the importance of considering foot flexibility when prescribing orthotics.  To ensure maximum therapeutic value from the orthotics, extra care and attention to the degree of compensation of the foot is vital.

It is not sufficient to simply measure a subtalar position or a forefoot angle in an attempt to quantify a deformity as to the number of degrees.  For example, one patient could have a 5 degree rearfoot varus deformity.  The foot is hypermobile of compensates fully.  This patient requires full rearfoot control.  Whereas another patient with the same 5 degree rearfoot varus has a tightly structured foot, small ranges of motion.  This patient will only compensate partially or not at all and require little if any control.  The previous example illustrates the importance of flexibility of the foot.  Or, if you will, is the foot uncompensated, partially compensated, or fully compensated?

Let’s take a closer look at compensation.  A foot which has an uncompensated subtalar varus deformity will show signs of callus formation or skin thickening on the entire lateral border of the heel and sole with a small discrete callus (usually not symptomatic) under the head of the 5th metatarsal bone.  That same foot partially compensated, will show less callus on the lateral border and less of a sub-5th metatarsal callus, but the callus might be symptomatic due to a now partially unstable 5th metatarsal bone.  We might even see the start of a sub-4th metatarsal callus. The fully compensated deformity would now move up and out of the way of the reactive force of the ground, thus eliminating any likelihood of any callus formation under the 5th metatarsal head. However, the 4th metatarsal head, which is the next most stable segment, might show evidence of shearing callus. 

The foot can be totally compensated and consequently unstable.  In this case the 1st and 5th segments would be hypermobile thereby exposing the 2nd and 3rd metatarsal heads to trauma resulting in a sore, diffuse callus under these metatarsal heads.  It should be apparent that the lesion distribution pattern must be considered as a valuable diagnostic determinant bearing heavily upon the type and degree of control of foot function that should be considered therapeutically.