Inside Insights On Orthotic Modifications

Pages: 28 - 32

   These expert panelists share their most commonly used orthotic modifications as well as insights on using highly inverted orthoses and the lateral Kirby skive.

Q: What are the most common orthotic modifications that you prescribe and why?

   A: Joseph D’Amico, DPM, most commonly employs a deepened heel seat at a standard size of between ¾ inches and 1 inch. He says a deepened heel seat enhances rearfoot control via better seating and positioning of the calcaneus. Dr. D’Amico notes this is particularly effective and critical in orthoses designed for patients with proximal plantar fasciitis, especially when the point of maximum tenderness is inferior. Dr. D’Amico cites Richard O. Schuster, DPM, who said in the treatment of heel pain, no heel seat is ever too deep.

   Richard Blake, DPM, commonly uses deep heel cups. These are normally 23 to 25 mm high medial and/or lateral, and he says they provide greater pronation/ supination control.

   In contrast, a high medial heel cup is helpful for Justin Wernick, DPM. He says DPMs often use a deep heel cup to control eversion of the calcaneus associated with subtalar pronation. However, he notes a deep heel cup/seat will occupy a great deal of room in the posterior part of the shoe, leading to difficulties with fit.

    “By using just an elevation of the medial border of the heel cup, we can resist eversion of the calcaneus in the shoe and reduce the bulk,” says Dr. Wernick.

   Both Dr. D’Amico and Dr. Blake commonly use metatarsal pads. Dr. D’Amico uses PPT® (Langer), noting that its closed cell foam resists deformation even after years of use. He prescribes a metatarsal pad for patients with a “dropped” transverse metatarsal arch, metatarsalgia or neuromas.

   Dr. D’Amico also employs metatarsal pads if he does not believe the amount of forefoot posting that he can place in the shoe will achieve the desired correction. Additionally, he uses a pad if there is increased pressure on metatarsals two, three and four as evidenced on computer assisted gait analysis. Dr. D’Amico notes metatarsal pads have been effective in the elderly to encourage plantarflexion of the digital segments, thereby improving stability and propulsion.

   Dr. Blake uses the metatarsal pads to relieve soreness distally. Likewise, he will use accommodative forefoot extensions to relieve areas of soreness directly by placing weight laterally, medially or both.

   Dr. Wernick commonly uses a forefoot extension to the sulcus. He notes that fabricating a functional device that extends to the cut lines will result in a slimmer device. However, in these situations, Dr. Wernick says the device tends to slide in the shoe, generally in a medial direction. Adding an extension of 1/6 inch or 1/8 inch of material can seat the orthotic and resist its migration, according to Dr. Wernick. He says this modification also adds some cushioning to the plantar surface of the metatarsal heads and will not take up any additional room in the shoe.

   Michael Burns, DPM, and Dr. D’Amico frequently use an extended forefoot posting. Dr. Burns says this modification permits him to maintain some “frontal plane control” of the foot after the heel leaves the ground during the propulsive phase of gait. Furthermore, the posting is particularly useful with rigid forefoot valgus, reducing the propulsive phase “over-supination” that might otherwise occur. He uses extended forefoot posting whenever the forefoot frontal plane variation exceeds 5 degrees and for all athletes who need any forefoot posting.

   Dr. D’Amico reserves extended forefoot posting for orthoses for athletic footwear. However, he will regularly prescribe this extended posting arrangement in the elderly to improve stability. He says the forefoot post extension should extend to the sulcus and be feathered distally. The material is butadiene rubber of varying durometer measurements to meet the weight and functional requirements of the patient, according to Dr. D’Amico.

   With almost every orthotic device, Dr. Burns will use rearfoot posting to try to stabilize the device at heel contact and to put the device in a position that allows some rock in the direction of eversion. He says this allows the normal pronation that must occur early in stance in response to the internal leg rotation. The effect of rearfoot posting is limited to this initial loading phase of gait and he notes it quickly loses any effect as the forefoot loads.

   Another common modification for Dr. Wernick is a medial arch platform. He commonly hears the complaint that the medial flange of the device irritates the arch of the foot, which is due to many factors but is usually a result of a tight calf. To help reduce the problem, he advises placing a medial arch platform on the positive cast. As Dr. Wernick says, this modification will turn the medial edge of the orthotic away from the foot, making the orthotic more comfortable to wear. In addition, he notes the medial arch platform has no effect on the height or contour of the arch so the device maintains full control of the foot.

   A reduced or omitted rearfoot undercut is another part of Dr. D’Amico’s armamentarium. As he says, most labs normally undercut the rearfoot by approximately 10 degrees to allow better shoe fit. However, he cautions that this also causes premature lateral post wear, resulting in lateral tipping of the device.

   Since many people today wear footwear with counters as wide as athletic type footwear, Dr. D’Amico says there is no need for a standard undercut. However, he notes those who wear a standard type dress or work shoe may still need an undercut. For sports footwear, Dr. D’Amico does not include the rearfoot undercut. He says this enables better rearfoot stability and alignment.

   Dr. Burns commonly uses a ¼-inch heel lift to compensate for equinus. He will also use the modification to take advantage of the “whole foot supination” that occurs with ankle joint plantarflexion. He reminds DPMs that ankle joint motion is triplanar and a significant amount of inversion and adduction often occurs with plantarflexion around the ankle joint axis.

Other Pertinent Modifications

   To help prevent the lateral stability that is sometimes associated with orthoses, Dr. Blake will use either a Denton modification or isolated lateral column reinforcement.

   Dr. D’Amico commonly uses a Morton’s extension to the interphalangeal joint of the hallux. He will add this extension to a forefoot varus post that has been extended to the sulcus or extend the distal arm of a Kinetic Wedge in the same manner. Dr. D’Amico says this modification extends the functional length of the first ray in Morton’s syndrome and plantarflexes a functionally hyperextended hallux segment, which improves weightbearing.

   Topcovers can be among Dr. Burns’ modifications. “I do not like topcovers used as ‘decoration’ but I like to use materials that add some usefulness to an orthotic device,” he says.

   To that end, he will use materials like closed cell neoprene (such as Spenco) to absorb shear forces to prevent blisters in athletes or skin shear in the insensate foot. His other common topcover materials include Plastazote (Zotefoams) or TufFoam to add some “dynamic molding,” particularly under the forefoot.

   A calcaneal inclination angle modification can be helpful for flexible adult onset flatfoot, opines Dr. Wernick. When the midtarsal joint collapses, he notes a lowering of the inclination angle of the calcaneus accompanies the collapse. To resist this lowering, he uses this modification to control sagittal plane motion at the midtarsal joint by supporting and resisting the distal portion of the calcaneus from dropping. He accomplishes this by removing 1/4 to 1/2 inch of material from the area under the distal calcaneus and the cuboid on the positive plaster cast, and then forming the shell to this contour.

   Dr. Burns often uses a plantar fascial accommodation. He prefers having an orthotic device fit exactly to the plantar surface of the foot when holding the foot in the position in which he is trying to encourage it to function. He says one accomplishes this fit with minimal alteration of the shape of the arch of the positive model (minimal arch fill). However, Dr. Burns notes that when the device fits so closely, some patients get irritation from the central band of the plantar fascia.

Q: What are the most appropriate indications for using a highly inverted orthotic such as the Blake inverted orthotic? Conversely, what problems have you encountered when prescribing such a device?

   A: Dr. Blake prescribes highly inverted orthotics for a severe pronated position with a resting calcaneal stance position (RCSP) of over 5 degrees everted. He also uses these orthoses for patients with severe pronation that is difficult to control with standard devices. He will likewise use the device for patients with severe alignment issues due to the high tibial varum needing foot inversion.

   When it comes to working with highly inverted devices, Dr. Blake says they may lead to too much supination. Other possible issues are irritation of the arch as the first metatarsal attempts to plantarflex. In addition, the device may lift the foot too high in the shoe, causing heel slippage or shoe irritation (especially in pes cavus).

   Dr. D’Amico prescribes the Blake inverted cast modification for peroneal spastic flatfoot secondary to subtalar arthritis or tarsal coalition, and also for posterior tibial tendon dysfunction/adult- acquired flatfoot. He will also consider the orthosis when treating a difficult to control hypermobile flatfoot with ligamentous laxity, especially in an obese patient.

   The problems Dr. D’Amico has encountered with the device include medial arch discomfort and lateral slippage. In many patients, he says one can avoid slippage with a lateral flange. However, when peroneal spasm is present, the force of pull may be too great to tolerate this modification. In addition, arch discomfort may be due to the foot trying to defeat the severe angular correction built into the device. Dr. D’Amico says this is especially true with adaptive shortening and/or spasm of peroneal tendons. He says supinatory exercises to stretch the peroneals can help prior to dispensing this type of orthotic. Incorporating a medial arch cushion into the device is often helpful, according to Dr. D’Amico.

   In contrast, Dr. Burns is “not a fan” of highly inverted orthoses. “The shape of the orthotic has to be altered too extensively in the arch and I like the shell to fit very closely to the arch of the foot in the position around which I am trying to control,” he explains.

Q: The successful use of a medial Kirby skive has been well documented. When would you choose to prescribe a lateral Kirby skive?

   A: Dr. Blake uses the lateral Kirby skive for supination problems. He notes that one can gauge the device’s success by temporarily placing felt on the present orthotic inside the lateral heel cup. If lateral instability improves, he notes one can send the positive casts back to the lab for a lateral skive. The lateral Kirby skive produces the best change in an already flat heel cup with vertical walls, according to Dr. Blake.

   Dr. Burns seldom uses a lateral Kirby skive. He says the device’s only indication is for lateral instability at heel strike and when the plantar projection of the subtalar joint axis falls under the lateral plantar calcaneal tubercle. If the axis projection is near the lateral aspect of the heel, he finds it more useful to incorporate a lateral flare on the heel of the shoe or consider some leg to foot control with an ankle foot orthosis.

   Similarly, Dr. D’Amico does not use a lateral Kirby skive modification. However, he does acknowledge the device’s potential value in reducing lateral rearfoot forces in a rigid cavus or uncompensated rearfoot varus foot with accompanying lateral instability.

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

Dr. Burns is the CEO of Burns Lab. He is a Fellow of the American Academy of Podiatric Sports Medicine.

Dr. D’Amico is a Fellow of the American Academy of Podiatric Sports Medicine. He practices in New York City.

Dr. Wernick is a Professor in the Department of Orthopedic Sciences at the New York College Of Podiatric Medicine. He is also a Diplomate of the American Board of Podiatric Orthopedics and is the Medical Director of Eneslow Comfort Shoes and Langer, Inc.

Dr. Valmassy is a Past Professor and Past Chairman of the Department of Podiatric Biomechanics at the California College of Podiatric Medicine. He is a staff podiatrist at the Center for Sports Medicine at St. Francis Memorial Hospital in San Francisco.

For further reading, see “Essential Pearls On Effective Orthotic Modifications” in the June 2009 issue of Podiatry Today.

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