Expert Insights On Effective Orthotic Modifications

Pages: 22 - 26
Author(s): 
Guest Clinical Editor: Russell Volpe, DPM

These knowledgeable panelists discuss prescribing heel raises, heel lifts, top covers and other modifications.

Q:

What strategies do you employ for effectively using heel raises and heel lifts in your orthotic prescriptions?

A:

Rarely are the left and right side of the human body exactly the same, according to Jeffrey Cusack, DPM. He says the resultant compensatory pelvic tilt in response to the asymmetric leg length may lead to sacroiliac arthralgia or even compression on the sciatic nerve. In this case, Dr. Cusack says equalization of the legs with an appropriate lift can be quite useful.

Barbara Pelc, DPM, says podiatric physicians can treat a forefoot equinus or small limb length discrepancy with an in-shoe lift. However, when using a heel lift to address a limb length discrepancy or equinus, Dr. Pelc says a shoe with a deep heel counter is necessary. Once the heel lift is at ¼ inch, she advises clinicians to consider having the lift added to the outside of the shoe to avoid the problem of coming out of the shoe, even with a deep heel counter.

Dr. Cusack notes the classic approach of a simple heel raise has generally been accepted for a leg length discrepancy of up to ¼ inch. He says one can compensate for any discrepancy greater than ¼ inch with a full lift tapered to roughly one-half the amount of the heel raise at the metatarsal heads. While the addition of a simple heel raise alone certainly improves the total contact of the foot against the supporting surface, he says it essentially fixes the ankle in a position of equinus. Dr. Cusack says a more progressive approach, even for leg length discrepancies as small as 2 mm, is to equalize the discrepancy with the use of a “full-sole” platform, thus maintaining a parallel relationship of the plantar surface of the foot to the ground. To enable more room in the toe box region, he says one can skive distally to the metatarsophalangeal joints (MPJs).

Robert Eckles, DPM, uses a subjective technique. If the ankle slowly dorsiflexes from the lateral forefoot with the knee extended and the hindfoot maintaining a “rectus” position, he seeks the place where the directed plantar pressure begins to cause frontal or transverse plane motion due to sagittal plane resistance. At that point, he evaluates the plantar angulation of the foot against the leg. Dr. Eckles would apply 1 mm of lift for each degree of plantar deviation from the perpendicular. As he notes, the technique does not measure how far the ankle could go but helps determine the relative stress the hindfoot is under from the posterior foot.

Regarding the use of heel lifts and shoe compatibility, Dr. Cusack says one will generally need to add lifts of greater than 7 mm to the outside of the shoe or (design permitting) within the midsole of the shoe itself. He cites several tricks to employ if one is also prescribing a foot orthosis. These include varying the thickness of the module of the left versus the right orthosis or employing a thinner module on the longer side. Another easy modification to the prescription is to instruct the laboratory to “grind the rearfoot post into the shell” on the long side only, effectively shortening that side, according to Dr. Cusack. By combining these two modifications, he says it is possible to realize a net lift of almost 3 to 4 mm on the short side.

While one needs to approach the use of heel lifts carefully so as not to induce any additional shortening of the gastrocsoleus complex, Dr. Cusack notes in patients with a true osseous blockade to ankle dorsiflexion, the use of a heel raise can truly improve function and lessen the pain associated with attempted ankle dorsiflexion during midstance. Whether secondary to an abnormality in dorsal talar anatomy or a convergence of the distal tibiotalar articulation, referred to as a tibial “procurvatum,” Dr. Cusack points out that these patients will never respond either to attempts to mobilize the ankle via stretching or even to a surgical approach via tendo-Achilles lengthening or gastroc recession. As he says, such patients actually function better if one leaves the ankle slightly plantarflexed. However, to offset the posterior shift in the center of mass that such an attitude induces, Dr. Cusack notes modest heel lifts enable the tibial segment to go back to a perpendicular position relative to the ground.

Q:

What are some of your frequently used positive modifications in your prescription writing and the indications/clinical circumstances in which you use them?

A:

Overpronated feet can be very challenging to approach, stresses Dr. Pelc. Depending on the severity of the situation, she cites some modifications that can help. When the patient presents with a relaxed calcaneal stance position of more than 5 degrees, Dr. Pelc says a Blake inverted cast modification will invert the foot/cast to increase the rearfoot position as well as control and reduce medial tensile stress.
Dr. Pelc notes another useful modification is the medial heel skive. She notes this will increase the support under the medial calcaneal tubercle, creating a more inverted rearfoot. Furthermore, she notes widening the device medially in the area of the longitudinal arch will increase the control during midstance.

Additionally, the Kirby skive and the Blake inverted cast are some useful positive cast modifications designed to decrease excessive medial compartment stress, commonly associated with cases of posterior tibial tendon dysfunction or plantar fasciitis, according to Dr. Cusack. In fact, for extremely pronated feet in which maximum below ankle leverage is required, he says a combination of both of these cast correcting techniques can be very helpful.

To provide stability to either a subluxing cuboid or lend additional stability to the calcaneocuboid joint in the presence of increased midtarsal joint stress, Dr. Cusack says the “cuboid notch” modification, or an enhancement of the lateral inclination angle or pitch of the calcaneus, can be effective. By removing about 3 to 5 mm of plaster in a directed manner from the plantar lateral aspect of the positive model beneath the cuboid, Dr. Cusack says one can achieve a more directed upward force to resist the plantar subluxation of the cuboid. He notes modification is also useful if one combines it with other motion enhancing techniques to improve overall first MPJ rotation during the active propulsive phase of gait.

Dr. Eckles prefers cuboid raises or stiffening under the lateral shell to stabilize the lateral column, which is beneficial over flanges and clips that have footwear fit issues. As he notes, a stiffened lateral column also more maximally pronates the oblique axis of the midtarsal joint and plantarflexes the fourth and fifth rays, which may also allow the peroneus longus an advantage, stabilizing the first ray. He almost always selects a tight fit for the shell with little lab fill but compensates by adjusting the flex of the material. Dr. Eckles believes the patient should not be able to pronate excessively onto the shell. He emphasizes the importance for proprioception so patients “feel” the shell, even if the device flexes underneath them and allows motion.

“I think the mechanical effect in the end is different than adopting a compensated position from the start,” says Dr. Eckles.  

Dr. Cusack says one can also incorporate accommodations for isolated plantar fibromas, lipomas or even a bow-strung medial band of the plantar fascia into the design.

Dr. Eckles almost always utilizes deep heel cups, except in the rare instances he is convinced that the rearfoot has no role in either generation of or compensation for the primary mechanical pathology under consideration. He almost always employs a heel lift, saying equinus is often occult and frequently a negative factor.

Intrinsic forefoot posting can also be useful to reposition the first ray and increase support in the area of the apex of the arch (base of first metatarsal and medial cuneiform), according to Dr. Pelc. For a foot that is abducting in the forefoot (midtarsal joint), she says a calcaneal pitch can be useful in stabilizing the lateral column.

Q:

What are your opinions on the use of top covers/soft tissue supplements at the foot/orthosis interface?  

A:

Dr. Eckles says soft tissue supplementation and “feel” are critically important. He says the elderly patients with diabetes and individuals with focal hot spots among others “absolutely require robust cushioning and impact management.

“Proprioceptive feedback, balance and general comfort, all of which may be enhanced by a conforming cover, are all vital parts of maximizing efficacy and adherence,” emphasizes Dr. Eckles.
However, Dr. Cusack says in the elderly population with known proprioceptive deficiencies (movement disorders, such as Parkinson’s, neuropathy secondary to diabetes, etc.), the addition of too generous (soft and thick) top covers can substantially reduce the feedback provided through the plantar pressure receptors of the feet. As he notes, combining 1/16-inch pink Plastazote over Poron of the same thickness provides not only reasonable shock absorption but actually enhances stability. Dr. Cusack adds that a smooth leather cover completes the package.

As patients ambulate, Dr. Cusack says they will, in a short period of time, begin to form a modest toe crest pad through the Plastazote interface. He says crest pads can significantly improve stability in the elderly. If necessary, Dr. Cusack says one can enhance the crest pads at a later time since the location as well as the individual (left may be different than the right) shape have already been dynamically established.

In any patient in whom one is considering either a digital crest pad or a metatarsal pad, Dr. Cusack strongly suggests following the same regimen: building the orthosis with the same dual density (1/16-inch Plastazote over the same thickness Poron) covering system but having the laboratory omit the final top cover. He says the patient should wear the orthoses for about two weeks and return to the office. At this time, he says a very clear location for installing either a crest pad or a metatarsal pad will become apparent, which the physician or fabricating lab can complete. Following what appears to be this “extra” step virtually eliminates the often multiple return trips back to the lab in an effort to get the pad in the right place, according to Dr. Cusack.

Dr. Eckles says supple top covers such as glove leather add an element of comfort and familiarity that may make a rigid device, which otherwise may not be tolerated, quite “friendly.” At the same time, Dr. Eckles thinks there are many elegant ways that one can use an uncovered highly polished device, footwear and socks permitting.

While the selective incorporation of a covering system can certainly improve the comfort factor, Dr. Cusack cites instances in which one can actually have “too much of a good thing.” In the 3- to 6-year-old pediatric population, he says control of the foot is often already compromised by the presence of the normal adipose tissue surrounding the very areas of the foot where physicians are attempting to exert maximum control. Accordingly, Dr. Cusack says the addition of anything but a minimal (1/16-inch) layer of material can significantly reduce the orthoses’ ability to exert a sufficient counterforce to the pronating foot. Dr. Cusack has seen instances in which so much material had been added to the surface of the orthosis that the child was actually standing on it rather than the calcaneus being contained within the heel seat region.

“Soft material between the orthotic shell and the foot can certainly begin to create issues after 1/8 inch in thickness,” says Dr. Pelc.

Dr. Pelc notes soft materials can often reduce or obliterate a deep heel seat. She says they can also increase the bulk of the device and alter how the foot will fit in the shoe with the device. Sometimes she notes a simple extension or a 1/16-inch Korex heel lift for shock absorption will do the job, avoiding the obliteration of the heel cup from the soft tissue supplement dorsally.

Dr. Cusack is an Assistant Professor in the Department of Orthopedics and Pediatrics at the New York College of Podiatric Medicine. He is affiliated with the Foot Center of New York in New York City and is a consultant to Advantage Orthotics Laboratory.

Dr. Eckles is the Dean of Clinical Studies and an Associate Professor in the Department of Orthopedics and Pediatrics at the New York College of Podiatric Medicine. He is affiliated with the Foot Center of New York in New York City.

Dr. Pelc is in private practice in Glen Head, NY. She is a consultant to Langer Biomechanics.

Dr. Volpe is a Professor in the Department of Orthopedics and Pediatrics at the New York College of Podiatric Medicine in New York City. He is in private practice in New York City and Farmingdale, N.Y.

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