Materials for orthotics

In order to understand why certain orthotic materials are typically recommended by podiatric physicians, it is important to understand the fundamental goals in orthotic therapy. The purpose of the functional orthotic is to accurately and precisely position the foot throughout the gait cycle so as to promote proper function. Its function is not merely to support the arch, as is often the case with commercial appliances or arch supports purchased in retail stores. The functional orthotic is prescription fitted and is very effective in alleviating symptoms and establishing proper alignment. In order to achieve the desired and expected results from the use of functional orthotics, several steps must occur. First, a detailed range of motion and muscle testing examination is performed by your podiatrist. The purpose of this is to measure and quantify the motion of all lower extremity joints, identify abnormalities such as excessive laxity or limitation of motion, and determine the weightbearing and non-weightbearing functional positions of these joints. The muscle testing portion of the examination is performed in order to determine muscle groups which may be excessively weak or tight and to determine their part in the overall cause of injury, symptoms or biomechanic problem.

Following the examination, a non-weightbearing neutral position cast of the foot is taken. The specific method of casting is critical and must be done accurately in order to achieve an accurate impression of the foot in its neutral position. The negative casts are then sent to an orthotic laboratory accompanied by a prescription written by your podiatrist indicating not only the specification for the correction of the positive casts, but also the materials to be used and the dimensions and accessories to be used in the manufacture of your functional foot orthotics. The manufacture of functional foot orthotics is thus a multi-step process involving detailed and intricate cast correction, orthotic fabrication and application of additional items prescribed by your podiatrist for the treatment of your specific condition.

In order to achieve the desired results, the functional foot orthotics must be made from materials which have the ability to resist the pathologic symptom-producing forces which have ultimately produced the injury. Typically, plastics or graphite are used, both offering a range of flexibilities, designed to appropriately resist abnormal injury-producing forces while allowing comfort and compliance so as to be compatible with the sport. The plastics that are used are generally made of a family of materials called polyolefins, the most common being polypropylene. The thickness of these materials ranges from 1/8" to 1/4". These materials range from quite flexible and compliant to relatively rigid. Graphite also ranges from quite flexible to quite rigid and is generally one-half as thick and one-half as heavy as orthotics made from polyolefin materials. The flexibility, or compliance, of an orthotic is a subjective choice determined by the requirements of your sport and the degree of rigidity required to resist the abnormal forces resulting in injury. Highly flexible devices are used when the forces imposed are relatively minor or the requirement of the sport mandates a compliant device. However, these materials possess shorter life spans due to the cyclic fatigue inherent in an orthotic device that has a high degree of flexibility. More rigid orthotic devices are used when more significant forces are present or the sport of choice is compatible with the more rigid device. More rigid devices have the advantage of being quite durable and can often last for many years without modification or adjustment. Typically, stop-start complex motion and/or cutting sports (ie. soccer, basketball, aerobics, tennis) require more compliance in an orthotic device, while repetitive-motion sports such as walking or running are quite compatible with more rigid devices.

Soft materials such as Neoprene, various open- and closed-cell foams or similar cushioning materials may be used in conjunction with functional foot orthoses to provide both support and comfort. A patient should always discuss these options with their podiatrist and even entertain the possibility of having more than one pair of orthotics using materials of different flexibility and/or covers as determined by the requirements of their sport, the constraints of their shoe gear, and their overall comfort.

Successful orthotic treatment should always include an orthotic device that is effective in reducing eliminating symptoms and is comfortable to wear. By selecting the appropriate flexibility material and cover material, both of these goals can generally be achieved.

William R. Olsen, DPM

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Materials for orthotics