Secrets To Making Effective Orthotic Modifications

These expert panelists explore making modifications to prevent medial arch irritation, limit over-supination and increase orthosis durability in athletes playing side-to-side sports.

Q:

What is the most common cause of medial arch irritation and what are your solutions for preventing and eliminating medial arch irritation in custom foot orthoses?

A:

Bruce Williams, DPM, has found that the most common cause of arch irritation is the lack of a first ray cutout in the orthotic. If the medial portion of the orthotic plate runs too far distally, he notes it will put pressure on the plantar fascia, triggering a functional hallux limitus response. Adding a properly sized cutout at the first ray along with some PPT or Poron to backfill the cutout will almost always eliminate the arch irritation, according to Dr. Williams. He notes that having inadequate arch fill or a medial column that is too stiff (i.e. thicker polypropylene shell) can also cause arch irritation. However, Dr. Williams cautions that one does not always have to lower the arch if the first ray can plantarflex uninhibited.

For Richard Blake, DPM, the most common cause of medial arch irritation is pronation control in an orthosis that is trying to support the medial column. The more the orthosis is attempting to correct, he notes, the greater the possibility for foot irritation. If the foot irritation is limited and one is using a polypropylene-based orthosis, Dr. Blake says simply grinding at the area of maximal irritation is curative.

“The medial band of the plantar fascia has been the most common cause of medial arch irritation in the custom foot orthoses I have made for patients over the past 32-plus years of practice,” says Kevin Kirby, DPM.

Dr. Kirby attributes this to the non-weightbearing casting procedure that most podiatrists use during negative casting. During negative casting, he says the plantar foot is only loaded slightly, which produces little tension force and little “bowstringing” of the plantar fascia within the medial arch. However, during weightbearing activities, he notes cadaver research has demonstrated that the plantar fascia is subject to tension forces that approximate the body weight of the individual during walking and running increases the plantar fascia tension forces even more.¹ In other words, weightbearing activities turn the plantar fascia from a soft, pliable ligament during negative casting to a rigid cord with over 100 pounds of tension force through the plantar fascia during the midstance phase of gait. Dr. Kirby says this can cause the plantar fascia to bowstring into the dorsal orthosis plate and cause plantar fascia irritation.  

The best way to avoid plantar fascia irritation with foot orthoses is to have the orthosis laboratory add a plantar fascia accommodation into the dorsal plate of the orthosis, notes Dr. Kirby. Otherwise, he says one will need to grind a plantar fascia accommodation into the dorsal orthosis shell to reduce the compression forces between the medial band of the plantar fascia and the dorsal orthosis shell. In some instances, when the physician or lab cannot grind the orthosis (e.g. composite orthosis shell), Dr. Kirby says one can salvage the orthosis by adding a 1/8-inch neoprene topcover to the orthosis with a plantar fascia “window” cut into the topcover to prevent the plantar fascia from being irritated during weightbearing activities.

If the orthosis has a plantar arch reinforcement, Dr. Blake notes one can remove some of that reinforcement in the small area of irritation. If the medial arch irritation is along the plantar fascia, he says the orthotic lab or physician can add a plantar fascia groove. Many times, the pronation control actually needs to be stronger or have a higher arch so the foot pronates onto the orthosis less, which he calls somewhat counterintuitive.

When the irritation is sports-related and one is trying to have the orthosis work in athletic and dress shoes, Dr. Blake cautions the orthosis could be too narrow for the athletic shoes. As a result, the device may be moving around in the shoe and is no longer matching up with the part of the foot the podiatrist intended to treat. In this case, he suggests making the orthosis wider as patients typically will only use it for athletic shoes at that point.

Q:

When making full-length foot orthoses for competitive athletes in side-to-side sports, what orthosis modifications do you use to increase the durability of the orthosis forefoot extension and topcover/bottom cover for these demanding sports?

A:

Dr. Blake typically applies a thin 2-ounce leather sealant on the bottom of the forefoot extension and the distal 1 inch of the plastic orthosis shell. He notes the leather’s texture can allow him to see wear in the device. Dr. Blake also cites use of the multi-color ethylene vinyl acetate (EVA) sheets for durability as topcover materials.

Dr. Kirby uses a leather topcover for patients involved in side-to-side sports with a topcover made of either 1/8-inch Poron or 1/8-inch Spenco underneath the leather. He notes bottom covers of leather or vinyl extending from the distal 3 cm of the plantar orthosis shell to the end of the toes of the forefoot extension may be necessary to protect the Poron or Spenco from being excessively abraded due to the large shearing forces generated at the forefoot of the orthosis in athletes involved in daily side-to-side sports activities.

Athletes involved in lateral movement sports “really wear down the topcovers on their devices very quickly,” says Dr. Williams. He notes 3 mm EVA is easy to use and durable in most instances. Although some athletes use Spenco-type topcovers, which are durable, Dr. Williams notes that Spenco also tends to retain moisture and bacteria, and can smell as a result. For the bottom covers, Dr. Williams will use textured rubber material, which minimizes slippage of the device in the shoe, adheres the forefoot extension to the orthotic shell and topcover, and provides more long-term durability.

Q:

What orthosis modifications do you use for patients who have symptoms such as peroneal tendinopathy and/or chronic inversion ankle sprains due to over-supination of the foot?

A:

Dr. Kirby says patients with laterally deviated subtalar joint axes, including those with a high degree of pes cavus, metatarsus adductus or “rigid” forefoot valgus deformity, will tend to suffer from symptoms caused by excessive subtalar joint supination moments. He says custom foot orthoses work best for these patients as they are designed to pronate the subtalar joint. Dr. Kirby acknowledges this is “totally contrary” to what many podiatrists learned in podiatry school.

Dr. Kirby has routinely used several foot orthosis modifications that “work extremely well,” including a lateral heel skive, a flat rearfoot post with no motion and a valgus forefoot extension of 1/8 to 1/4-inch Korex and lateral arch filler. As he explains, the lateral heel skive acts to shift the ground reaction force more laterally on the plantar rearfoot to increase the subtalar joint pronation moment. He says the flat rearfoot post prevents the rearfoot portion of the orthosis shell from inverting relative to the ground.

Finally, Dr. Kirby notes the valgus forefoot extension increases the ground reaction force on the lateral metatarsal heads to increase the subtalar joint pronation moment at the forefoot and the lateral orthosis arch filler prevents the lateral longitudinal arch of the orthosis from deforming (i.e. flattening) under load from the foot. In addition, he notes the orthosis medial arch is lower than normal and may be balanced 2-5 degrees everted to increase the valgus correction to the whole orthosis.

Dr. Blake will make custom orthotic devices for supinators, saying there is no OTC orthosis for athletes who supinate. He tries to set the cast at heel vertical, noting he has had only a handful of patients who need a 3-degree everted pour to stop the foot from supinating.

Dr. Blake adds a lateral arch fill (Denton modification) along the cuboid to the fifth metatarsal head. Although this is not supposed to be a valgus wedge, he says a valgus wedge of 1/8 inch down the whole lateral side of the orthosis, typically stopping shy of the toes, is sometimes necessary. In supinators, Dr. Blake will flat post the extrinsic rearfoot posts instead of grinding motion. As he notes, one can also add forefoot extensions of 1/8 inch to 3/16 inch, grinding rubber under the fourth and fifth metatarsal heads. He says one can ask the orthotic lab to place a high lateral heel cup (he has gone up to 28 mm) and a lateral flange along the lateral side of the orthosis (keeping the lateral heel cup height and extending that further toward at least mid-shaft on the fifth metatarsal). Dr. Blake says some practitioners do want the typical medial arch support to be several millimeters lower.

Dr. Blake adds that one can ask for a lateral Kirby skive in the mold before pressing the plastic, even extending that out to the calcaneocuboid joint (extended lateral Kirby skive).

For Dr. Williams, modifications for over-supinators depend on patients’ resting calcaneal stance position in relation to their neutral stance position. He cites the use of the maximum pronation test to determine how much, if at all, the lateral column can raise off the floor when the patient is in stance and trying to maximally pronate the subtalar joint. If patients cannot get the lateral column off the floor, Dr. Williams says adding a valgus forefoot post will be “painful and potentially injurious to them.”

Dr. Williams says the maximum pronation test can also show if the rearfoot can pronate at all. Often, he notes the subtalar joint is maximally pronated in stance and has little, if any, range of motion (ROM) left to pronate. If the patient is maximally pronated at the heel, he suggests using a lateral heel skive of 1-2 degrees. Dr. Williams says this carries little risk and good benefit to trigger pronatory forces in that area. If patients can pronate more, he says one can still use a lateral heel skive and/or post the whole lateral column in valgus 1-4 degrees, depending on the ROM of pronation of the lateral column.

“These custom foot orthoses for patients with supination-related pathologies are some of the hardest to make but, when done correctly, are literally life-changing medical devices for these individuals who often walk with chronic foot and/or ankle pain due to their overly supinated feet,” says Dr. Kirby.

Dr. Blake is a Past President of the American Academy of Podiatric Sports Medicine. He is in private practice in San Francisco.

Dr. Kirby is an Adjunct Associate Professor within the Department of Applied Biomechanics at the California School of Podiatric Medicine at Samuel Merritt University in Oakland, Calif. He is in private practice in Sacramento, Calif.

Dr. Williams is the Director of Gait Analysis Studies at the Weil Foot and Ankle Institute and the Weil Foot-Ankle and Orthopedic Institute. He is a Past President and Fellow of the American Academy of Podiatric Sports Medicine. Dr. Williams is the Director of Breakthrough Sports Performance, LLC in Chicago.

Reference

1.     Fauth AR, Hamel AJ, Sharkey NA. In vitro measurements of first and second tarsometatarsal joint stiffness. J Applied Biomechanics. 2004; 20(1):14-24.