Evaluating Forefoot Modifications And Materials In Custom Orthotics

With the prevalence of forefoot pathology, there are a litany of options available to podiatrists when prescribing custom orthoses. Here the panelists discuss their experience and rationale for various choices, including posts, extensions and pads.

Q: In your practice, do you have any particular forefoot materials or modifications that are “go-to” options for your orthotics? How did you arrive at this conclusion and for what conditions do you find yourself using them?

A:

Richard Blake, DPM, says that, when dealing with orthotics for great toe joint limitation, one needs to differentiate functional from structural. He continues to say that functional hallux limitus should respond with orthotic devices that reduce pronation and off-weight the big toe joint with dancer’s padding (aka reverse Morton’s extensions). Dr. Blake then adds that in structural hallux limitus/rigidus, he typically does not try to give the big toe joint more motion, but stresses one must be aware that crowding the toe may produce more pain.

“So, it is a gentle balance between further restricting the joint with orthotic devices via built-in Morton’s extensions, and not crowding the area,” he explains.

“The restriction you get from Morton’s extensions sometimes has to come from rocker shoes, like HOKA^® One One, spica taping, or just stiff shoes. In general, I find functional hallux limitus needs higher arches and hallux rigidus lower arches. Hallux rigidus may be better with no orthotic device or a full-length, stiff orthotic device.”

Vilayvanh Saysoukha, DPM, MS, FACPM, AACFAS shares she is a fan of and believer in:

• the efficacy of metatarsal pads for neuromas, metatarsalgia, and fat pad atrophy;

• a Morton’s extension for a rigid painful first MTPJ or dorsiflexed first ray;

• a reverse Morton’s extension for a plantarflexed first ray;

• an aperture or “U” cutout if there is a very prominent metatarsal head with significant hyperkeratosis and pain;

• a metatarsal bar if there are multiple prominent metatarsal heads, fat atrophy and hyperkeratoses;

• a kinetic wedge for functional hallux limitus to preload the first MTPJ during gait; and

• a toe crest or toe bar for hammertoe deformities.

Robert D. Phillips, DPM feels there are two reasons for orthotic modifications in the forefoot. The first is to change the direction of forces under the foot, and the second is to supplement soft tissue defects. Common forefoot modifications that he uses include a varus or valgus posting to invert or evert the orthotic more than the original cast sits on the ground.

“This is a wedge under the anterior edge of the orthotic, and I want the hardest material I can find,” he says. “Unfortunately, most offices don’t have the equipment to utilize the same material that the orthotic was made from. However I find that a very solid cork-rubber blend works well for making adjustments in the office while a patient waits. This type of material does wear down with time and will need to be built up every three to six months.”

He also uses a forefoot eversion onlay, which is a wedge added on the top of the anterolateral quarter of the orthotic. Dr. Phillips again stresses that he prefers a very solid material with very little compression, such as cork-rubber materials. For fat pad atrophy and/or muscle atrophy, he usually pads the entire orthotic, including the metatarsal fat pad area distal to the MTPJs.

“Two materials I have success with are neoprene and Poron^®, though in the past few years I find myself using Poron much more because due to its longevity and ease in grinding if I need to bevel it,” he adds. “I usually cover Poron with leather. I have tried viscoelastic materials, however I have observed less success due to their inability to return energy into the system.”

Lastly, for lesion accommodation, Dr. Phillips says he usually uses a fairly firm material, such as a medium rubber, except under the lesion, where he replaces the firm material with a much softer material or sometimes no material at all.

Q: When do you find that using a forefoot extension is important? Are there any particular materials you prefer for this?

A:

Dr. Saysoukha shares she uses a Morton’s extension for turf toe, a rigid, painful first MTPJ or dorsiflexed first ray. Accordingly, she uses a reverse Morton’s extension for a plantarflexed first ray.

“Most of my patients cannot tolerate stiffer materials, such as a forefoot extension of a polypropylene shell,” she adds. “I find my patients better tolerate crepe, Corex, or EVA materials.”

Dr. Phillips notes, as he previously mentioned, he feels the most common use for a forefoot extension is to add extra accommodation for areas of excess pressure that produce pain, calluses and ulcers.

“The material that I find least effective is Plastazote^®, as it bottoms out very quickly under higher pressure areas,” he says. “Poron is a good cushioning material which I utilize more than any other. I have done durometer tests on a wide variety of soft materials, and find that Poron has the lowest durometer on the OO scale than any of the others carried by our prosthetics lab.”

In his experience, Dr. Phillips relates that most patients with diabetes need forefoot extensions to supplement fat pad atrophy and also the increase in stiffness of the fat pad, which is the hallmark of increased advanced glycation end-products (AGE) cross-linking the collagen.

He points out that an important part of cushioning materials is replicating the normal mechanical function of the fat pad under the metatarsals.

“The fat pad is rather soft when the MTPJs are in their resting position, but as the MTPJs dorsiflex, the fat pad gets harder; in other words, Young’s modulus of elasticity is low during the contact period of gait and increases in the propulsive period of gait,” he explains. “In this way it takes the vertical force from the ground needed to produce upward acceleration of the center of body mass and transfers it to the skeleton. Unfortunately, we haven’t developed a single orthotic material that has this property. Viscoelastic materials absorb shock well, but don’t return that energy back into the system. So, they actually increase the work of walking. The best we’ve come up with so far are elastic materials, though we need to have materials with the lowest hysteresis (when there is very little difference between the slope of the stress-strain curve when the load is applied and when the load is released.”

Dr. Blake adds that, in general, he finds that first ray cutouts de-stabilize the medial column support so it is low on his list of orthotic variables.

“I also try to stay away from anterior orthotic posts (especially those with a varus bias) since they can block first ray plantarflexion,” he says. “When a patient has big toe joint pain, I try to make my orthotic device full-length as much as possible. The typical orthotic length stops behind the first metatarsal head and increases the motion there, while decreasing the motion in the metatarsal shaft and midfoot. So, the painful area becomes the most stressed area.”

Q: In what situations do you find yourself using a metatarsal pad in a custom orthotic?

A: Dr. Phillips says that he seldom orders an extrinsic metatarsal pad with his custom orthotics. Since the intention of the metatarsal pad is to allow the first metatarsal to plantarflex and to separate the lesser metatarsals, he points out that a non-weight-bearing supine cast usually provides enough first metatarsal plantarflexion and one may actually plantarflex the first metatarsal during the casting procedure, if necessary.

“If there is a lot of mobility in the lesser tarsometatarsal joints, then, when taking a plaster mold, I also stroke the central metatarsal heads on the plantar aspect to keep them from plantarflexing from the weight of gravity,” he says. “If you use a foam box or semi-weight-bearing cast, you seldom get enough first metatarsal plantarflexion, thus you will want to order a metatarsal pad.”

Dr. Phillips does use an extrinsic metatarsal pad when support for the central metatarsals is necessary distal to the metatarsal heads, as with neuromas.

Dr. Blake states that most casting procedures (even scanners) at best capture the skin outline under the metatarsal shafts.

“The metatarsals typically need more elevation to hold the bones upward under the second through fourth shafts,” he says. “All metatarsal pain syndromes can be improved by adding metatarsal pads in general on top of the custom orthotic device, and also many propulsive phase instabilities can be improved with metatarsal support.”

Dr. Saysoukha adds metatarsal pads for generic ball of foot pain, neuroma pain and accommodation for patients with fat pad atrophy.

“A metatarsal bar can work well with fat pad atrophy with very prominent and painful metatarsal heads and hyperkeratoses,” she explains. “Both forefoot accommodations can help prevent wound recurrence as well.”

Q: In what situations do you find yourself using a forefoot post? Do you usually prefer intrinsic or extrinsic, and why?

A:

In Dr. Saysoukha’s practice, she uses a forefoot post mostly for athletes with medial tibial stress syndrome, plantar fasciitis, fatigue and moderate forefoot and rearfoot varus or valgus. She adds she finds that a three-degree varus crepe extrinsic post works well with a gait pattern that has very little to no heel strike and more of a toe-to-toe type gait, which she sees in activities such as running, sprinting, football, golf, basketball, tennis and racquetball.

“I usually prefer extrinsic forefoot posting for easier removal or modification if the patient cannot tolerate it,” she concludes.

Dr. Blake says in relation to posts, it is a balance of pain relief and function. At times we want to limit the motion due to pain, at times we want to allow the foot to move freely. He also adds that educating patients on the biomechanics of posting and whether the expectation is for temporary or permanent use is important.

Dr. Phillips relates excellent results using intrinsic posting for the severe forefoot valgus, although conversely he notes challenges with posting for forefoot varus with respect to comfort and achieving the desired result.

“I’ll order three to five degrees of intrinsic forefoot varus posting, and anything beyond that I’ll order extrinsically,” he advises. “If the resting calcaneal stance position is more than five degrees everted, or if there is a medially displaced subtalar joint axis, I start to think about using the Blake inverted orthotic technique. A great many runners also benefit from the Blake technique.”

Q: What aspects of your biomechanical and/or physical exam do you find most important in determining optimal forefoot materials and modifications for your orthotics?

A:

During her exam, Dr. Saysoukha first determines the level of flexibility or rigidity of the rearfoot. After placing the rearfoot in neutral, she says she evaluates the position of the first ray and if there is forefoot valgus or varus.

“I also take into consideration patient feedback on what materials they can tolerate, their activity level and the durability of material needed,” she says.

Dr. Phillips below shares key points of his examination when focusing on determining forefoot materials and modifications orthotics, in order of importance, although he stresses that different presenting symptoms may alter this order.

• Resting and neutral stance tibiocalcaneal angles.

• Center of calcaneal bisection translation with the tibial bisection in neutral stance.

• Forefoot-to-rearfoot relationship in subtalar joint neutral and with the subtalar joint pronated

• Plot of subtalar joint axis on plantar foot when subtalar joint is in neutral

• Contracture of the triceps surae and hamstrings

• Leg length evaluation

• Jack’s test

• Muscle testing for weakness

• Internal-external rotation problems 

Dr. Blake is in practice at the Center for Sports Medicine, which is affiliated with St. Francis Memorial Hospital in San Francisco. He is a past president of the American Academy of Podiatric Sports Medicine.

Dr. Phillips is retired from the Orlando Veterans Affairs Medical Center in Orlando, Florida where he was previously program director for the Podiatric Medicine and Surgery Residency and maintains an appointment in the education department. He is a Diplomate of the American Board of Foot and Ankle Surgery and the American Board of Podiatric Medicine.

Dr. Saysoukha is a Diplomate of the American Board of Podiatric Medicine, a Fellow of the American College of Podiatric Medicine and an Associate of the American College of Foot and Ankle Surgeons. She is in practice in McMinnville, TN.