Orthotics function as a wedge.
This may appear to be an over simplification of the therapeutic design characteristics of all foot control devices. (prescription orthotics, over the counter arch supports, insoles or orthopedic devices)
Those who have used a variety of foot control devices, as a patient or as a treating physician, know that there are several unique design characteristics described in the literature. You also know that none of these design modifications consistently provide any significant improvement from the basic contoured wedge design. The value of orthotics/arch supports/orthopedic devices is well documented in the literature, there however is little agreement as to the value of any specific design modifications.
Early researchers studied the anatomy of the foot and defined three arches. The medial longitudinal, lateral longitudinal, and transverse metatarsal arches. Most authors agreed that all three arches function together and that the medial longitudinal arch was the primary arch. Function of the two secondary arches were directly related to the position of the the main long arch of the foot.
More recently scientists who study human bio-mechanics have defined this collapse as PRONATION. This collapse of the arch during function is thought to be causative for many chronic foot, ankle, knee, hip, and back conditions.
Efforts to address this collapse and subsequent internal rotation of the lower extremity, have been ongoing for more than 200 years. Hundreds of devices that are used during walking and standing to decrease pronation of the foot, and stop excessive internal rotation of the knee and hip joints, many use the modifications described below, but ALL use a wedge, placed with the apex or high point near the center of the medial longitudinal arch.
Some of the design changes described in the literature include the following.
Deep heel cups. To this very day many practicing physicians believe that a deep heel cup is necessary to create optimal function of a foot control device prescription or otherwise. Clinically no consistent measurable benefit is observed even with the deepest of heel cups. This is supported in the patent literature where most describe the heel region of their device as “Cupola” in shaped. functioning like a ball an socket this part of the device corresponding with the heel of the foot will spin or rotate no matter how pronounced the cup design. Other than helping the shoe hold the foot directly on top of the wedge portion of a support device a deep heel cup has little to do with overall function.
Lateral Flange: This elevation of the outside of a device is a design which has not been very popular with podiatric physicians. Even though it also helps the shoe hold the foot on the highest part of the wedge portion of the device, it is not all that effective, and if the shoe is wide and lets the foot slide over the top of this design , it digs into the tissue and creates pressure and irritation.
Medial Flange Most physicians who treat patients with prescription orthotics recognize that the benefit of treatment with an orthotic device is related to the height of the wedge. this logical belief that a higher wedge would help more has caused many to try a design characteristic know as a “high medial flange”. When you look at a finished prescription orthotic with a “high medial flange” it looked like the wedge is very high. Unfortunately when the device is use in most patients it provide no additional help, causes irritation to the inside of the arch, and takes up more space requiring a larger shoe. Understanding this “increase wedge” medial flange dilemma was a requirement before Theta could be defined and quantified accurately. Most clinicians now acknowledge that medial flange design has no real benefit in controlling the foot and stopping the pronation that causes the disability and symptoms. Theta research defines the part of the wedge that relates directly to foot function and the part of an orthotic device know as the medial flange in not part of the measurement.
Intrinsic and Extrinsic posts are basically wedges that are applied in a way to stabilize the device in a MORE wedged position. Conceptually this increases the wedge that corresponds with the medial longitudinal arch and does in fact provide more angular support with less collapse of the arches and pronation of the foot. Prescription orthotics produced by many current orthotic laboratories use these techniques to alter the wedge from what the cast impression actually shows.
This is a photo of a Rhoadur plastic orthotic, heat contoured to a positive mold of a human foot. The contoured plate is then tilted additionally with an intrinsic varus post of 20 degrees in the forefoot and with a 20 degrees varus extrinsic acrylic post in the rear-foot. It represents the techniques we used to fabricate our orthotics during the first 8 years of our basic research.
When Theta research first began fabrication techniques used neutral position non-weight bearing casts to form plastic plates heat contoured and shaped to the foot and fit in a shoe. Angular design was first quantified using these functional custom devices. As different as these early orthotics look from the full length covered rubber orthotics that we use today they use the same wedge to stop the pain.