Emerging Insights On Orthotic Prescriptions And Modifications

Author(s): 
Guest Clinical Editor: Paul Scherer, DPM

Q:

Do you use functional orthotic devices to treat the functional limitus component of hallux abducto valgus (HAV)? What change do you think the orthoses make to improve the symptoms?

A:

Jenny Sanders, DPM, does use functional foot devices in these patients. She cites a study by Roukis and colleagues, who proposed that reduction in the first metatarsophalangeal joint’s (MPJ) maximum degree of dorsiflexion with dorsiflexion of the first ray is the predominant cause of hallux abducto valgus and hallux rigidus.3 Additional studies have shown that functional orthotics increase first MPJ dorsiflexion by improving the position of the first ray in the sagittal plane.4 Dr. Sanders notes the authors of another study also suggest that in functional hallux limitus (FHL) caused by an abnormal dorsiflexed first ray, one can gradually restore hallux dorsiflexion by using foot orthoses to control the abnormal rearfoot position, which improves the first ray position.5

   Dr. Kashanian feels one can easily treat the functional hallux limitus deformity associated with a hallux abducto valgus with both intrinsic and extrinsic orthotic modifications. For an intrinsic cast modification for the pes plano valgus foot type, Dr. Kashanian uses a minimal cast fill along with a 2 mm Kirby skive and 2 degree inversion technique, which offloads the medial column and prevents excessive pronation.

   Likewise, Dr. Choate uses a reverse Morton’s extension in nearly all patients with functional hallux limitus. Since a dorsiflexed first ray is the primary issue behind functional hallux limitus, she notes a forefoot valgus wedge has been shown to provide the ultimate means of reducing tension in the plantar fascia and “unlocking” the forces leading to first ray dorsiflexion.6 In addition, Dr. Choate tries to recognize any forces, such as an everted calcaneus, that may lead to dorsiflexion of the first ray. She notes that she addresses control in the orthotic prescription with modifications such as medial skive and a deep heel cup.

   For an intrinsic cast modification for the pes cavus foot type, Dr. Kashanian will prescribe minimal cast fill and a deep heel cup, which offloads the forefoot and allows more stability to the midfoot. As far as an extrinsic modification for both foot types, she uses a reverse Morton’s extension to offload the first ray and thus prevent excess jamming of the first MPJ.

   Dr. Sundstrom notes functional foot orthoses bring the subtalar joint to neutral in order to lock the metatarsal joints and stabilize the medial column. As she says, most patients with HAV have some degree of mobility, if not hypermobility, in the first tarsometatarsal joint.

    “With the exception of excessive STJ pronation, this may be the greatest contributing factor to the development of the deformity in the first place,” notes Dr. Sundstrom.

   Due to this flexibility, Dr. Sundstrom notes an orthotic should be able to reposition and stabilize the medial column, and improve the position of the first ray.

Q:

Do you use functional accommodations such as sweet spots and plantar fascial grooves in your rigid or semi-rigid orthotic devices, and what are the indications?

A:

While intrinsic accommodations can be helpful, Dr. Choate rarely uses plantar fascial grooves. She has historically found the placement and depth of plantar fascial grooves challenging. Dr. Choate prefers to use a reverse Morton’s extension in an attempt to decrease tension in the plantar fascia.6

   In contrast, Dr. Sanders routinely uses plantar fascial grooves with both rigid and semi-rigid orthotics. As she notes, since pes cavus feet almost always have a tight plantar fascia, even without a diagnosis of plantar fasciitis, she will incorporate a plantar fascial groove into her orthotics. When it comes to patients who have plantar fasciitis with a tight plantar fascia, Dr. Sanders emphasizes that adding a plantar fascial groove is essential to ensuring a comfortable orthotic device due to the increased plantar fascial thickness.4 Dr. Sanders also uses intrinsic accommodations or depressions in the orthotic plate material to off-weight areas like a prominent navicular.

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