These encompass a wide range of devices, from semi-rigid devices with modest control and cushioning, to soft devices which distribute weight evenly via the principle of total contact. The latter, widely used for diabetic and rheumatoid feet, utilize materials that conform to the foot, such as closed cell foams. The advantage is that more weight is borne by the arch, and less weight is borne by the metatarsal heads and other normal weight bearing areas. The disadvantage is that these devices lack the durability of other orthotics, and frequently bottom out. A diminished fat pad in a geriatric patient is managed in a similar way, distributing weight to normally non-weight bearing areas.
Semi-rigid devices can be used to relieve the pressure of a plantar flexed metatarsal by a cutout under the metatarsal head, or to redistribute weight away from any bony prominence. They can utilize a toe crest to support and relieve pressure from hammertoes, mallet toes and claw toes. They can also be used to redistribute weight away from the central portion of the heel in plantar fasciitis. In addition, Semi-rigid devices provide a combination of cushioning and mild functional support for arthritic feet in geriatric patients.
Materials for Fillers and Accommodative Devices
Open Cell Foams: Offer good evaporation and heat dissipation characteristics.
Polyurethane Foam: Includes PPT/Poron, Ovaflex, Corlyte, and Vylite. Relatively durable. Good shock absorption. Used in forefoot extensions, top covers, and arch fill.
Spenco: This neoprene sponge bonded to a multi-stretch nylon fabric is capable of absorbing side-to-side forces (anti-sheer), as well as vertical pressure. Suitable for abrupt stopping and starting (sports.) Not heat moldable.
EVA: Ethyl vinyl acetate foam. Durometer of 40.
Closed Cell Foams: Offer good insulation and conforming properties.
Plastizote: Closed cell polyethylene. Comes in three densities, with durometers of 15, 23 and 40. Soft plastizote compressed as much as 20-30% without rebound, but with good force distribution. Low and medium densities are used as top covers to protect neuropathic feet or to accommodate plantar lesions. Aliplast and Pelite are in the same family. Pelite is non-allergenic. These materials eventually bottom out.
Corks: These highly shock absorbing and flexible materials are available in heat moldable and non-heat moldable forms. Examples of heat moldable corks are Thermocork, Birkocork and Ucocork. Non-heat moldable include Korex and Orthocork. Corks are used primarily for posting, arch fill and forefoot expensions. Heat moldables can also be used for accommodative shells.
Laminates: Laminated combinations of two or more materials combine the best qualities of those materials. One commercially available material, known as Diab-a-sheet, combines a bottom layer of energy absorbing PPT with a top layer of moldable plastizote. Another example is Tri-lam.
Corrections and Accommodations
There are many corrections and accommodations that can be specified by the Podiatrist. Some of the more common ones are:
Metatarsal Bar Pad: To transfer weight from the metatarsal heads proximally.
Dancers Pad: Metatarsal pad with a first ray cutout, to enable the first ray to seek its own level.
2-4 Met Pad: To redistribute weight away from the heads of plantarflexed metatarsals 2-4.
Heel Spur Pad: A ÒUÓ shaped pad to relieve pressure from the area of calcaneal insertion of the plantar fascia.
Heel Cushion: For those patients with a decreased heel fat pad.
Morton’s Extension: Employed to limit ROM at the 1st MPJ when there is a short 1st Metatarsal, or Hallus Limitus or Rigidus with pain upon ambulation.
Toe Crest Pad: For those patients with hammertoes who have experienced greater foot comfort with a a crest pad supporting digitally contracted digits.
Neuroma Pad: A raise just distal to the metatarsal heads of the affected interspace, to spread the metatarsal heads and relieve the symptoms of the neuroma.
Neuroma Plug: Similar to a neuroma pad, but smaller and placed directly under the interspace between the metatarsal heads.
Schaphoid Pad: A raise under the medial arch, to allow for more cushioned pronation in a rigid device.
Individual lesions under the metatarsal heads can be accommodated but cutouts, providing the orthotic has sulcus for full length extension.
Materials frequently used as top covers for their unique properties include Poron, Pelite, Spenco, and Plastizote. Naugahyde, a vinyl material with an appearance similar to leather, is frequently used because of its durability and cosmetic appearance. Naugahyde is available in many colors, can be readily cleaned, and maintains its original appearance for a long time. Cowhide breathes, but is susceptible to sweat and wear. Sweat resistant cowhide is available. It will discolor, but not breakdown with excessive perspiration. Horsehide, a more durable leather, is available. Also, for those applications where slip resistance is needed in a thin appliance, suede brown leather is available. Suede brown is less than half the thickness of conventional cowhide. Considerations must be made for allergies when selecting a topcover material. Suede is frequently used as a bottom cover for accommodative devices for cosmetic purposes. While it gives the orthotic a nice, finished appearance, it can also complicate adjustments.