Key Insights On Modifying Orthoses For Specific Conditions

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Guest Clinical Editor: Ronald Valmassy, DPM

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.

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