Ensuring Orthotic Efficacy For Adults And Children
- Volume 24 - Issue 8 - August 2011
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In addition to sharing their perspectives on rearfoot posting, these expert panelists discuss their approaches to assessing the effectiveness of their orthotic prescriptions and when it is time to replace orthoses.
How do you determine the type and amount of rearfoot posting you prescribe?
Russell Volpe, DPM, prefers extrinsic rearfoot posting. He says it provides stability to the device along with the desired frontal plane correction. Dr. Volpe only switches to intrinsic rearfoot posting if there is a low volume in the counter of the intended shoe.
“By using intrinsic rearfoot posting, you reduce the bulk of the device in the shoe but you do sacrifice some of the stabilizing effect of the post,” says Dr. Volpe.
Dr. Volpe has several ways to determine the amount of rearfoot posting on a device. Most commonly, he works from the degree of rearfoot (subtalar and tibial) varus he identifies during the biomechanical exam. Typically, Dr. Volpe says half the measured deformity is a good starting point to determine the amount of posting. He often increases that amount in pediatric flatfeet and in lax foot types.
Most of the time, Ronald Valmassy, DPM, attempts to provide an inversion or supinating force to the orthotic device. Using the Root technique, he will typically invert the device anywhere from a vertical position to 5 to 10 degrees of inversion, depending on the degree of calcaneal eversion in the resting calcaneal stance position (RCSP). For example, if the patient is 5 degrees everted, Dr. Valmassy will normally invert the device by approximately 8 to 10 degrees. If he is utilizing the Blake inverted casting technique, he will typically multiply the degree of eversion by five.
In addition, Dr. Valmassy customarily adds a medial calcaneal Kirby skive in lengths from 2 to 6 mm. If the heel is everted 1 or 2 degrees, he uses a 2 mm skive and for a heel everted up to 5 degrees, he typically utilizes a 4 mm skive. Dr. Valmassy notes that anything beyond 5 to 6 degrees of eversion will typically require a 6 mm medial skive.
If the patient is supinated and everted in RCSP due to a forefoot valgus deformity and exhibits marked lateral instability, Dr. Valmassy will balance the rearfoot to a perpendicular position and typically adds a 2 mm, 4 mm or 6 mm lateral calcaneal skive. For patients who are laterally unstable but maximally pronated and still inverted, he will attempt to iatrogenically introduce a forefoot valgus correction into the casts while taking a neutral position cast.
Similarly, Dr. Volpe sometimes uses a tissue stress model and prescribes medial skive modifications to the heel cup to shift the orthotic reaction force more medially on the subtalar joint. He notes this results in applying a greater supinatory moment to the subtalar joint. Sometimes, Dr. Volpe combines these two techniques for added effect. He also makes adjustments to the post for different clinical scenarios such as extending the post medially, omitting undercut (medial or lateral) and grinding the post into the shell for bulk reduction.
As Paul Jordan, DPM, notes, a separate rearfoot post is rarely required for young children. He suggests considering the consistency of mature heel contact as well since the ability to achieve a consistent heel contact with weight acceptance is not evident until ages 6 to 8.
In children ages 6 to 8, Dr. Jordan says there may be sufficient frontal plane malalignment of the lower limb-rearfoot complex to initiate an excessive and prolonged pronatory moment from initial heel contact to midstance. For these children, he says the degree of rearfoot posting should be the amount required to retain the subtalar joint around its age-appropriate neutral position.