Accommodations, Additions, Modifications
The most common important special additions and extensions to custom orthotics are listed below. There are many others which are an adjunct to foot orthotic devices and their design is only limited by a practitioners' innovation.
When writing the orthotic prescription, it is important to specify whether a special addition, modification or accommodation is needed either bilateral, left only or right only. To avoid confusion, clearly write out either Bilateral, Left or Right. Hand written abbreviations like B, L, R with a circle around the letters are frequently unclear.
Rearfoot Posts: Stability of the orthotic is increased with a rearfoot post. Because the heel cup of an orthotic is relatively round, the device will tend to invert and evert depending on the moment of force. An extrinsic rearfoot post changes the rounded surface to a flat surface which helps to resist unwanted inversion or eversion, especially at the heel contact phase of gait. An intrinsic rearfoot post is basically a flat grind off of the bottom of the heel cup material. This results in small circular flat area, the size of which depends on the thickness of the shell material. An intrinsic RF post is also known as a spot grind.
There does not appear to be any evidence that supports the idea of grinding the lateral aspect of the bottom of the post to provide a 2 to 4 degree inversion of the heel. However, the thought is that it helps to prevent early pronation at heel contact.
Extending the extrinsic rearfoot post on the lateral aspect may be effective in the treatment of lateral ankle instability. Also, grinding the lateral aspect of post vertical or with out any bevel may provide additional stability for the ankle. Our standard is to grind the sides of the extrinsic RF posts at a 15 degree angle. This helps to fit the orthotic within the counter of the shoe.
Strip Heel Posts: Posts which include only the front (distal) 1/2 of material on the heel of the device. This reduces the bulk at the posterior aspect and aids in fitting the orthotic in some shoes.
Metatarsal Pad: A tear-drop shaped Poron pad, which is convex or rounded superiorly with the distal aspect wider than the proximal aspect. It is positioned on top of the device and extends from the front edge of the orthotic shell proximally to about the level of midshaft of the lesser metatarsals and is as wide as the distance between the 2nd and 4th metatarsal heads. The pad can be positioned at any location necessary to help off load the heads of the metatarsals. You should specify the thickness of the pad as, very thin (1/16"), thin (1/8"), moderate (3/16") or thick (1/4").
Metatarsal Bar: A 1/8" thick Poron addition applied to the distal aspect of the shell extending from medial to lateral and extends proximally about 1.5" from the front edge. It is beveled slightly at the distal and proximal margins. This helps to off load all of the metatarsal heads. In order to provide additional off loading of the met heads, you can request no bevel on the front edge.
Reverse Morton's Extension: A Korex addition which extends from the distal aspect of shell to the sulcus under the 2nd, 3rd, 4th and 5th metatarsal heads. This is intended to increase first MPJ dorsiflexion range of motion. This addition is most commonly used when treating functional hallux limitus and hallux abductovalgus. It may also be used to off load the sesamoids. The default thickness of Korex we use is 1/8". It can also be made using 1/16", 3/16" or 1/4" thick material.
Morton's Extension: A 1/8" thick Korex (or firm EVA) addition which extends from the distal aspect of shell under the 1st MPJ distally to the hallux IPJ. This can be effective to help off load the 2nd metatarsal when either an acquired or congenital elevation of the first metatarsal head exists. Rigid Morton's extensions made by extending the polypropylene orthotic shell out to the end of the hallux may help to limit 1st MPJ motion. The area where the extension meets the front of the orthotic shell often times develops a stress fracture in the polypropylene.
Heel Pad, with and without accommodation: 1/8" Poron applied in the heel cup area which is either a full pad,or is shaped like a horse shoe in order to accommodate the tuberosity of the calcaneus and absorb shock.
Neuroma Pad: this is a convex shaped pad placed in the area between the metatarsal heads. It starts at the proximal third of the metatarsal shafts and ends just proximal to the metatarsal heads. The location must be stated and it is best to mark the casts. It is intended to cause a slight separation of the metatarsals and alleviate intermetatarsal neuroma symptoms.
High Medial Arch Overlay Padding: an extension of the top cover cushion above the medial arch of the shell which helps to cushion the medial aspect of the talo-navicular area.
Forefoot Accommodations: Accommodations can be provided by either making cut outs in the top cushion material or as an additional piece of material applied to the orthotic. When the accommodation is made in the cushion material, it is usually necessary to apply a cover over the cushion. Therefore, Spenco, Neolon and other materials which have the cushion material laminated to the fabric cover should not be cut out.
When ordering accommodations it is necessary to provide marks in the impressions for the exact location and size of the accommodation. It is more accurate to place transferable marks on the foot prior to casting than to draw the marks after taking the impressions. Be aware that marks made on the foot when non weight bearing may not be in the specific location that the patient needs them when weight bearing. Therefore, you might want to have the top cover only cemented on the posterior 1/2 and not have the accommodations made in the orthotic extension initially. Have the patient wear the devices for a week or so and the pressure points will usually be identifiable. The accommodations can then be made accurately and the top covers fully cemented. The accommodations can be either a round hole (punch out) or a slot out.
You should specify whether you want the accommodation made in the cushion material (i.e. Poron) or in an additional piece of Korex, EVA or Poron and specify the thickness. The default thickness is 1/8". However, 1/16", 3/16" and 1/4" thick material can be used. Accommodations using EVA can be made of either soft (35 durometer) or firm (65 durometer) material.
When ordering a forefoot accommodation as an addition to the shell, our default is to bevel it onto the device at the front of the shell (Bevel On Device-BOD). Some practitioners prefer that the proximal edge of the addition begin at or abut the front edge of the shell and extend out to either the level of the sulcus or the end of the toes (Front Edge Out-FEO).
EVA Plantar Arch Fill: EVA of medium density applied under the shell and ground flat will prevent deformity of the orthotic and increase the rigidity. This may be necessary for obese patients. It is also required when a lift is applied from the heel to the full length of the shell, sulcus or toes and when plantar wedges are needed.
Forefoot Varus and Valgus Wedge Extensions: additional material (usually Korex or EVA) applied to the shells and extending to the sulcus to help support forefoot varus or forefoot valgus conditions. The degree of wedge or thickness of the wedge should be specified.
Heel lifts: material added to the plantar aspect of the devices and the thickness should be specified either in fractions of an inch or millimeters. The lift can be added just to the rearfoot post, full length of the shell, to the sulcus or toes. Consider the design of the shoes when ordering heel lifts over 1/4".
Cuboid Pad: a rounded pad positioned under the cuboid which is intended to invert the bone.
Toe Fillers: a plastazote piece of material that is shaped to fill the void following loss of digits. Poron is applied to the surface of the plastazote that contacts the stump. When ordering toe fillers, it is necessary to provide the lab with a well formed plaster cast of the foot that captures the stump of the foot. Foot scans and foam impressions are not adequete in most cases. Also, we requre that the patients' shoes be sent along with the cast.
Extrinsic Medial Heel "Skive": a wedge shaped piece of material that is applied to the inside of the medial aspect of the heel cup. This is an addition that can be added to a device which did not have a medial heel skive originally made on the positive in the cast correction and modification process. Also know as a varus heel cup wedge.
Intrinsic Shell Modifications
Concavity in shell: One of the most common types of intrinsic shell modifications is a concave shaped area formed into the material. This is intended to off load specific pressure points on the plantar aspect of the foot where the shell makes contact.
Concavity in shell with Poron fill (Sweet Spot): A sweet spot is a concavity which is filled with Poron in order to provide an accommodation and additional cushion. When ordering concavities it is necessary to provide marks in the impressions for the exact location and size of the concavity. You should also indicate the depth of the concavity as either shallow, moderate or deep. It is more accurate to place transferable marks on the foot prior to casting than to draw the marks after taking the impressions.
First Metatarsal Head Cut Out: The medial corner of the shell is cut out starting from the lateral aspect of the 1st metatarsal head and ending proximal to the 1st metatarsal neck. This is intended to allow plantar flexion of the 1st ray. The shape of the cut can be either straight/angled or rounded.
First Ray Cut Out: The medial corner of the shell is cut out starting from the lateral aspect of the 1st metatarsal head and ending proximal to the 1st metatarsal base. This is intended to allow additional plantar flexion of the 1st ray.
Heel cup apertures (heel holes) are circular holes made thru the full thickness of the center of the heel cups which help to reduce the bulk in that area and may also work as an accommodation for a painful area at the center of the heel. Filling the aperture with Poron will offer additional cushion for the heel accommodation.
No bevel to the front edge of the orthotic shell may provide offloading of the metatarsal heads. This is more effective when the shell is polypropylene rather than the thinner composites.