Using rearfoot posts on custom foot orthoses has become a mainstay of orthotic therapy in podiatry. However, it has been shown that measuring neutral position of the subtalar joint via inversion and eversion of the calcaneus is flawed in terms of its reproducibility. Studies concerning whether neutral position of the subtalar joint is a viable method of assessment have questioned the foundation of podiatric biomechanics. Yet in offices around the world, the 4-degree varus rearfoot post seems to be a standard approach.
With this in mind, our expert panelists offer their take on this issue.
Q: What are your thoughts on using rearfoot posting?
A: “As mentioned, there are some legitimate questions about the accuracy and reproducibility of neutral subtalar joint measurements,” explains Russell Volpe, DPM. Robert “Daryl” Phillips, DPM, takes it a step further, noting that it is “important to realize rearfoot posting has very little to do with the non-weightbearing measurement of subtalar joint motion.”
Dr. Volpe feels the purpose of an extrinsic varus rearfoot post is to stabilize the device against the ground and to control or limit the frontal plane component of subtalar pronation with varus angulation of the calcaneus. If your objective with the foot orthosis is to limit either the degree or speed of pronatory motion of the subtalar joint during gait, then Dr. Volpe says a rearfoot varus post is indicated.
According to Dr. Phillips, the rearfoot post changes the angle the orthotic can assume inside the shoe as the foot strikes the ground, and it decreases the longitudinal flexibility and torsional flexibility of the orthotic once the anterior edge of the orthotic accepts weight. Unfortunately, Dr. Phillips contends no one has an objective way of directly measuring either the angle of the orthotic inside the shoe during gait or of measuring the orthotic deformation inside the shoe during gait.
As a result, Drs. Phillips and Volpe say their decisions on rearfoot posting are often based on clinical experience.
Dr. Phillips says in the “old days” of orthotic making, when he and most practitioners made their own orthotics, heel posting was not a standard practice. Most of the time, he recalls, DPMs would dispense the orthotics without a heel post. Then when patients returned for follow-up visits, they would add the heel post only if the patient or the doctor was not 100 percent satisfied with the result.
“This means a great many patients’ symptoms were adequately alleviated with no heel posting,” notes Dr. Phillips. “When it was added, most of the time we started with a 4-degree motion heel post and then adjusted it according to patient satisfaction and our own observation of the gait pattern.”
In some instances, adding rearfoot posting can make the patient’s condition worse, according to Howard Dananberg, DPM. He says that plantar fasciitis in the flexible cavus foot is one of the most difficult problems to treat in podiatry and he believes that rearfoot posting, in some ways, contributes to this failure.
When these patients undergo in-shoe pressure testing, Dr. Dananberg notes there is invariably a sharply lateral weight flow off the heel and toward the outside of the foot. “Building a custom foot orthoses that incorporates a varus post only serves to shift weight further laterally, causing an increased instability and additional strain to the plantar fascia,” explains Dr. Dananberg.