Functional Prescription Orthoses

The functional prescription orthoses used to treat patients in this study are orthopaedic devices that are designed to promote structural integrity of the joints of the foot and lower limb by resisting ground reaction forces that cause abnormal skeletal motion to occur during the stance phase of gait.

The design follows the basic principles developed by Root et al. in the 1960s

The material used in the manufacture of the functional orthoses is a semi-rigid polypropylene. This has been found to be the optimal material for use in such devices. It is relatively inexpensive, can be manufactured by 3D cad-cam, computer controlled milling technology which is both accurate and reproducible. Polypropylene is also light in weight and volume as well as being extremely durable. It can be modified easily, if necessary, by the prescribing practitioner.

Rigid or semi-rigid material for the use of orthotic manufacture has been found to be more effective and comfortable in relieving a variety of musculo-skeletal symptoms than more flexible material such as EVA. There is a near absence in the literature of reported complications resulting from the use of rigid or semi-rigid orthoses.

Following a thorough and comprehensive biomechanical examination to establish the ‘normal’ or ‘ideal’ lower limb alignment of the patient (forefoot to rearfoot, rearfoot to lower leg), a 3D scan is taken to capture the shape of the plantar surface of the foot while the foot is held in this ideal alignment with the subtalar joint in a neutral position and the midtarsal joint fully pronated.

After 3D reconstruction of this scan by computer software, the forefoot to rearfoot alignment is assessed. If this corresponds with measurements taken in the biomechanical examination, then the scan has faithfully captured the ideal shape and alignment. The scan can easily be taken again if necessary.

Measurements are also taken in a weight bearing position, of the alignment of the lower one third of the lower leg as well as the heel (a line drawn bisecting the posterior aspect of the calcaneus). This is the resting calcaneal stance position which indicates the degrees of pronation that has occurred from the neutral calcaneal stance position (which is the sum of the tibial alignment and subtalar neutral measurement). Measurements of the weight bearing foot and the shoe are also taken to determine the dimensions of the orthoses.

From the calculations of measurements taken during the biomechanical exam and those taken weight bearing, a prescription is determined. This, together with the 3D scans are sent to the orthotic manufacturing laboratory.

The prescription includes the material thickness, position of rearfoot heel cup (an increased inverted angle would increase the subtalar joint pronation control), forefoot alignment (in relation to the rearfoot as measured in the biomechanical exam and from the 3D scan – perpendicular, varus or valgus), dimensions of the shell and accommodation for plantar fascia, short 1st metatarsals and prominent styloid processes. Lastly the angle of rearfoot posts, including a bevel to provide adequate shock absorption in gait through pronation at heel contact, and a heel post elevator angle to prevent rocking of the orthoses in the shoes.

If you need advice on prescription orthotics, book an appointment with one of our podiatrists for an assessment.

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