Key Insights On Modifying Orthoses For Specific Conditions
- Volume 21 - Issue 10 - October 2008
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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.