Quantifying an Orthotic Design

Quantification of orthotics  beyond current standards is necessary so as to produce devices that can be evaluated scientifically.

Historical Review

Records from the United States patent office use many different names to describe those inventions intended to improve foot and or arch function the "Orthotic". Detailed review of over 70 different registered inventions describes only two basic design techniques for orthotics. One technique builds a device by placing mass or substance in the arches of the foot; the other fabricates a plate-contoured to the plantar surface of the foot.

Many orthotic devices currently used today and first presented almost 100 years earlier strategically place mass so as to generate support to the medial longitudinal, lateral longitudinal and transverse metatarsal arches. Earlier orthotic inventions used the patients foot, then individual foot impressions and later shoe size formulas to generate the design of their arch supporting orthotic devices. Foot and or arch supports (orthotics) constructed in this fashion were recorded in both early and more recent patent literature.

Other inventions describe fabrication of a plate contoured to the plantar surface of the foot, using milling and bending techniques to contour the material to foot impressions or scanned coordinates. This contoured plate was further stabilized with a heel post designed to control the position of the plate during weight bearing or stance phase of the gait cycle. Additional varus wedging to the contoured plate, up to 10 degrees, has been described. Both extrinsic posts and intrinsic posts (changes in the contour of the plate from its original configuration) are described. Numerous variations in plate width and material used for construction are recorded. Review of the patent literature identified designs as early as 1924 that contoured metal, rubber and wood to cast impressions taken from individual feet. Many orthotic laboratories, using a variety of plastics and even a scanned digital image as the foot impression currently use this contoured plate method of fabrication.

Many types and combinations of material both natural and synthetic have been used to construct the orthotic devices reviewed. Some use materials that are soft and said to "cushion the foot". Others use material that is highly resistant to deformation, with expressed intent to support or stabilize. Many incorporate materials that both support and cushion foot function.

Orthotics constructed of steel, wood, plastics and hard rubber have all been used to generate relatively rigid plates. Foam rubber, water, air and a variety of compressible materials have been used as cushions for the foot.

In general inventions designed to fill the arches used softer materials, than those who contoured a plate did. Function of a foot control devise is increased with a material less deformed during stance phase of gait. The term functional orthotic, currently used to describe semi-rigid to rigid contoured plate orthotics may be generally applied, however all foot control devices alter the function of the foot.