There is a difference between the orthoses prescribed by Podiatrists and other health professionals. An analogy is the difference between spectacles prescribed by optometrists and those one can pick up ‘over the counter’ from a pharmacy.
The science of lower limb and foot biomechanics and orthotic therapy was researched and developed by podiatrists in America. This was introduced to Australia in the 1980s and ’90s. This is an exact science and involves the detailed qualification and quantification of lower limb alignment and joint range of motion. Along with a detailed assessment of gait and postural alignment these measurements are used to determine an individual’s ideal – or functionally efficient position.
Once this ideal functional position for the foot and lower limb has been established from the biomechanical assessment, a plaster cast or 3D scan is taken to capture the shape, alignment and forefoot to rearfoot relationship in this position. Orthoses are then manufactured to this shape, incorporating posts, or additions, which control the position of the foot in relation to the ground and the leg as well as the range of motion that occurs in the joints.
The greatest force exerted on the foot during walking or running is ground reaction force through the big toe. This is equal to the force exerted by body weight, which, during toe-off can be multiplied 4 times. Controlling this deforming force requires a rigid or semi-rigid material, which with modern manufacturing techniques can be light and thin but very strong, enabling them to fit into most footwear. Unfortunately, prescription orthoses made to exact measurements are expensive to manufacture, though they do last a long time.
Because they conform to the shape of the foot in its ideal position and can maintain an efficient position from heel strike to heel off, they are usually very comfortable, if a little strange at first. Even though the material, usually polypropylene, is rigid, or semi-rigid it can still be adjusted to provide more or less control as well as comfort.
As with all orthoses, they should be comfortable, fit in the shoes that need to be worn and provide the control to resolve the problem.
By comparison, premade or ‘off-the-shelf’ orthoses are soft and flexible and control by means of their bulk rather than material strength. They therefore take up more room in the shoe and can (usually) only be worn in ‘sport’ shoes. Soft orthoses do, however, fit well and are comfortable in football boots and running spikes
Once the value of orthoses was established, entrepreneurs decided that everyone should benefit and began manufacturing less expensive orthoses from flexible EVA foam to a standard shape and promoted their sale to the public and health professionals including Podiatrists. Some of these premade orthoses can be modified to provide comfort and control, however, because they are flexible, they cannot control forefoot to rearfoot motion and are much more bulky, making them difficult to fit in fashion shoes. They are not so exact in their control as prescription orthoses, therefore the person prescribing them does not have to be so exact in the patient examination and diagnosis. This enables health professionals, who have not been educated in the exact science of lower limb and foot biomechanics, to use them in their treatment arsenal.