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.
Q: How do you determine the appropriateness of the 4-degree rearfoot varus post and what clinical signs would suggest not to use it?
A: Dr. Dananberg says there are various clinical signs he uses to determine whether a 4-degree RF varus post is acceptable. For example, what if the patient’s foot appears pronated in stance, but the outside of his shoes (lateral aspect) shows excessive wear? If so, the patient is inverting while walking and posting will only compound the issue, according to Dr. Dananberg.
You should also check for calluses on the feet and determine whether they’re lateral or medial in location, advises Dr. Dananberg. “If they are predominately lateral and the skin sub 1st metatarsal head is smooth and soft, then posting may again compound the situation,” he explains.
If you see excessive contraction of the lesser digits in conjunction with the above findings, Dr. Dananberg says the patient has a strong inversion component to his or her walking, so using an RF post is contraindicated.
Overall, Dr. Dananberg feels the best way to determine the appropriateness of rearfoot posting is to use in-shoe pressure testing to determine the nature of weight flow and then post accordingly. Dr. Volpe recommends a three-pronged approach:
Assess the varus angulation of the rearfoot (tibia and subtalar joint);
Consider the clinical condition(s) you are treating; and
Consider the purpose and objectives of the foot orthosis.
Dr. Volpe prefers to assess the rearfoot varus (subtalar and tibial varum) during the biomechanical exam in order to determine the appropriate degree of posting. He says a lower combined rearfoot varus assessment yields a lower rearfoot angulation and a higher deformity requires a higher angulation.
Dr. Volpe may increase the angulation in patients who have a high valgus compensation of the rearfoot on weightbearing, ligamentous laxity or other signs of severe pronatory deformity.
This method, which results in rearfoot posts from 0 to 8 degrees in most cases, should help you identify when the standard 4-degree varus post is contraindicated, according to Dr. Volpe. He adds that in most cases in which you’re prescribing orthotics for shock absorption, weight dispersion, etc., and limitation of pronation is not an objective for the orthosis, a 4-degree rearfoot post would be high and a lower angulation would be recommended. On the other hand, he notes he is more likely to use a high rearfoot post when he wants to limit the extent or duration of pronation in the gait cycle or if clinical circumstances call for inversion of the rearfoot.
When it comes to clinical signs for not using a 4-degree rearfoot varus post (or other high rearfoot varus posts), Dr. Volpe says you should be wary of a varus relaxed calcaneal stance position, lateral heel callus or a history of inversion lateral ankle sprains or lateral ankle instability. Also, if your patient demonstrates a lateral shift or excessive lateral weightbearing in the stance phase of gait, Dr. Volpe says you should avoid high rearfoot varus posting.
Since orthotic laboratories have taken over the creation of these devices for clinics, Dr. Phillips says podiatrists must decide whether to use heel posting at the time they write the orthotic prescriptions. While there are certain guidelines (see “Key Guidelines On Heel Posting”) that he follows when treating patients, Dr. Phillips says heel posting is “very much in the realm of a clinical art.” In his experience, a 1-degree change in heel post motion can be very helpful or hurtful.
“The clinician has to be aware of the heel post motion and is left many times to experiment with it, increasing or decreasing until achieving the right result,” sums up Dr. Phillips. He says this requires you to make small adjustments in an office setting and you should emphasize to your patients that these adjustments are “still very much a part of the orthotic therapy process.”
Dr. Dananberg (shown on the right) practices in Bedford, NH.
Dr. Phillips is the Director of Podiatric Residency at the Coatesville Veterans Affairs Medical Center in Coatesville, Penn.
Dr. Volpe is a Professor and Chairman of the Department of Pediatrics at the New York College of Podiatric Medicine. He is also the Medical Director of Langer, Inc.