Key Insights On Modifying Orthoses For Specific Conditions

Author(s): 
Guest Clinical Editor: Ronald Valmassy, DPM

Given the variety of conditions one sees in practice and ­­the challenge of ensuring optimal results with orthoses, expert panelists offer their take on utilizing orthotic modifications for different case presentations.

Q: What modifications would you make for a patient who has flexible forefoot valgus, excessive midstance and propulsive phase pronation?

A: As Richard Blake, DPM, notes, a flexible forefoot valgus pronates late in the gait cycle because it initially supinates in contact phase. He emphasizes that control of this foot primarily depends on four factors. The first factor is capturing the forefoot valgus during the casting or scanning process.
“Impression foam techniques never do a great job on this,” points out Dr. Blake.

Second, the lab should fully support any forefoot valgus that the cast captures. Third, Dr. Blake says the shoe must be
supportive on the outside or lateral aspect to hold on to the force that the orthosis generates. Finally, the foot should be stable enough to change with the force created by the orthotic. For example, he notes that prior ankle sprains have not damaged the lateral ligaments too much so they do not hold with the correction.

Dr. Blake notes that “labs that do not know how to control forefoot valgus” must rely on UCBL devices or varus wedging of the late midstance pronation. He typically uses a Root device and strives for perpendicular balance with 5/32-inch polypropylene (which may be heavier based on weight), 23-mm lateral and 21-mm medial heel cups with a 0-degree extrinsic rearfoot post, and maximum forefoot valgus support. One should place the full correction of the device just behind the head of the metatarsal, according to Dr. Blake.

When dispensing the orthotic, Dr. Blake says one of three things will happen: the control will be perfect; the control blocks rearfoot supination but still allows forefoot pronation; or the control still allows some contact supination and propulsive pronation.

Normally, Dr. Blake says one can alter the device to control these forces at least temporarily. He says those alterations include a Denton modification, a reverse Morton’s extension or valgus wedging for the supination, and medial arch fill or Morton’s extension for the pronation.

Kevin Kirby, DPM, says one should not solely determine the treatment of patients with foot orthoses based on the patients’ forefoot to rearfoot relationship or by the gait examination findings. Rather, he suggests the major determinants in the design of foot orthoses should be the specific injured or symptomatic anatomical structure, and the types of forces (such as tension, compression or shearing) that are causing the injury to that anatomical structure.

For example, if the patient with a flexible forefoot valgus,
excessive midstance and propulsive phase pronation has stage I posterior tibial dysfunction, Dr. Kirby would use an orthosis to decrease the tensile force within the posterior tibial tendon by exerting a STJ supination moment on the foot. To do so, one should invert the orthosis 2 to 3 degrees with a 2-mm medial heel skive, a 16-mm heel cup and minimal medial expansion plaster.

However, Dr. Kirby notes if the patient with a flexible forefoot valgus, excessive midstance and propulsive phase pronation has a peroneus brevis tendinitis or tendinopathy, he would treat the patient very differently than the patient with posterior tibial dysfunction. In the patient with a peroneal tendinitis or tendinopathy, Dr. Kirby says the orthosis should decrease the tensile force within the peroneus brevis tendon by exerting a STJ pronation moment on the foot.

Accordingly, he would make the heel of the cast vertical and would also add a 2-mm lateral heel skive and an increased medial expansion plaster thickness to the positive cast along with a valgus forefoot extension to the orthosis. The end result would be an orthosis with a valgus wedged rearfoot and forefoot, and a decreased medial longitudinal arch height in order to increase the STJ pronation moment acting on the foot during weightbearing activities.

“Using this ‘tissue stress’ approach to orthosis therapy is the key to optimum therapeutic results with foot orthoses,” maintains Dr. Kirby.

Q: What modifications would you make for an 8-year-old patient who has compensated tibial torsion with severe adduction and marked subtalar joint (STJ) pronation?

A: This type of patient compensates primarily at the midtarsal joint as well as the subtalar joint, according to Justin Wernick, DPM. He adds that the pronation at the STJ only expedites the range of motion at the midfoot.

Dr. Wernick recommends using a thermoplastic device with a deep heel seat, rearfoot posting and lateral and medial flange (UCBL, DSIS) with a calcaneal inclination modification. As he notes, abduction and dorsiflexion of the forefoot is associated with adduction and plantarflexion of the rearfoot during a closed chain.

Dr. Wernick says one should use a calcaneal inclination modification to resist the distal end of the calcaneus from plantarflexing, which resists flattening of the foot. This treatment requires enhancing the lateral arch of the orthoses with the apex of the modification just proximal to the cuboid, according to Dr. Wernick. He also emphasizes the importance of a shoe with a rigid counter and deep heel seat.

As Dr. Kirby notes, a child with reduced tibial torsion will tend to have an adducted gait pattern. However, he points out that the patient will often compensate for his or her adducted gait pattern by maximally pronating the subtalar joint in order to abduct the gait further. Accordingly, emphasizing strong anti-pronation moments in the orthosis prescription would be a mistake, according to Dr. Kirby, as this orthosis would only lead to further gait adduction by supinating the subtalar joint.

When designing the orthosis, Dr. Kirby says DPMs must decide whether the child would receive more therapeutic benefit from being less pronated or from having a more rectus angle of gait. Generally, if treating an otherwise asymptomatic child with this type of clinical presentation, he will design the foot orthosis with only a mild correction for the STJ pronation. Dr. Kirby will combine this with either a gait plate design or with a valgus forefoot extension to try to abduct the child’s forefoot in order to make the gait less adducted.

Dr. Blake notes that transverse plane deformities and compensation with STJ pronation are the most difficult to control.

He says transverse plane pronation, such as internal tibial torsion and internal femoral torsion, causes a severe pronatory force with marked talar adduction. He notes the efficacy of the standard orthotic prescription with frontal plane control of varus or valgus deformities producing talar inversion or eversion forces. Dr. Blake cautions, however, that stopping severe talar adduction requires advanced orthotic prescriptions.

For the aforementioned 8-year-old patient, Dr. Blake initially would prescribe a 35-degree inverted orthotic device with a high 27- to 30-mm heel cup and a 2- to 3-mm Kirby skive. This tactic should generate a sufficient supinatory force against the talar adduction to neutralize it. Dr. Blake says this will hold the heel near a vertical position. To maintain that medial column support, he also orders maximal width held together with a 0-degree extrinsic rearfoot post.

Dr. Blake adds that a semi-rigid 3/16-inch polypropylene shell with medial phalange should work well. When utilizing the inverted technique for these severe pronatory forces, if one notes undercorrection with the first device on either foot, he suggests increasing the supinatory force by several mold adjustments prior to repressing. The mold adjustments include an additional 2-mm Kirby skive, an additional 1/8-inch medial column correction, and an additional 10-degree inverted cant.

Q: What modifications would you use for lateral instability in a patient who functions with the subtalar joint maximally pronated yet is still inverted in stance and in gait?

A: In a patient with lateral ankle instability, Dr. Kirby says the biomechanical problem that causes the ankle instability could be one of three mechanical factors. He says there may be some structural abnormality in the foot or lower extremity that is causing excessive STJ supination moments. Alternately, there may be relative weakness within the peroneal muscles, which actively resist supination or there may be some structural defect within the lateral ankle ligaments, which are the anatomical structures that passively resist supination when STJ supination occurs suddenly during weightbearing activities.

When it comes to patients with lateral ankle instability, Dr. Kirby suggests designing the foot orthosis to increase the subtalar joint pronation moments in order to counterbalance the subtalar joint supination moments that result in inversion ankle sprains. If the patient with lateral ankle instability has an inverted calcaneus but is maximally pronated at the STJ, he says one should design the foot orthosis to increase the STJ pronation moments even though the foot is already maximally pronated.

One can do this by ordering a vertical heel balancing position with a 16-mm heel cup, a 2- to 3-mm lateral heel skive, a flat rearfoot post and a valgus forefoot extension, according to Dr. Kirby.

“These orthosis design modifications will shift the ground reaction force acting on the patient’s plantar foot more laterally so there will be an increase in subtalar joint pronation moments and less likelihood that there will be some sudden increase in inversion moments that will cause another inversion ankle sprain for the patient,” explains Dr. Kirby.

In addition to the specially designed foot orthosis, he says one may use high top shoes/boots or modify the shoes with a lateral sole flare to give further supination stability to the patient.
A patient with a partially compensated rearfoot varus (i.e. maximally pronated at 3 degrees inverted) is only a diagnostic challenge, according to Dr. Blake. He says such a patient is maximally pronated yet stands inverted. “When the medical world or non-medical world gives this patient an orthotic that forces him or her to a vertical position, the patient cannot tolerate them,” notes Dr. Blake.

Dr. Blake notes one must tell the lab to pour the cast in the patient’s maximally pronated position (i.e. 3 degrees inverted). Then one should use 27- to 30-mm heel cups (sort of a modified UCBL device). He says such patients are severe pronators in function but they are severely supinated to the ground. One should treat the pronation more or the supination more, advocates Dr. Blake. He says physicians can normally achieve this with a 0-degree rearfoot post and a Denton modification to stabilize the lateral column (arch fill under the lateral arch without valgus wedging).

Dr. Blake adds that propulsive phase supination control may be necessary with 1/8- to 3/16-inch sub 4/5 valgus support and with maximal forefoot valgus support if it exists in the foot.

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

Dr. Kirby is an Adjunct Associate Professor in the Department of Biomechanics at the California School of Podiatric Medicine at Samuel Merritt College. He is the Director of Clinical Biomechanics at Precision Intricast 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.

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

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