Key Insights On Orthotic Casting And Function
Our expert panelists discuss the pre-casting workup for orthotics, the advantages of plaster casting and the importance of checking range of motion. They also offer pointers on what you should look for before sending casts to the lab and troubleshooting when patients say their orthotics are not working correctly.
What biomechanical assessments optimize a pre-casting workup for functional orthosis?
Denise Freeman, DPM, details the most common assessments she performs before writing an orthosis prescription.
Forefoot to rearfoot angular relationship. This allows her to diagnose an inverted or an everted forefoot deformity. This assessment also facilitates a decision about the amount and degree of forefoot posting, according to Dr. Freeman. She also checks this later when evaluating the negative cast.
Neutral calcaneal stance position (NCSP). This measurement permits her to diagnose a rearfoot deformity such as rearfoot varus or valgus.
Relaxed or resting calcaneal stance position (RCSP). As Dr. Freeman says, the RCSP reveals if the foot has had to pronate or supinate to compensate for any deformities in the kinetic chain. She calls the RCSP a useful measurement when deciding how much medical skive she will incorporate into the orthosis shell.
First metatarsophalangeal joint (MPJ) range of motion. Dr. Freeman advises measuring this in both NCSP and RCSP. She says it is useful when deciding whether to add a reverse Morton’s forefoot extension.
Limb length. Although she does not routinely assess limb length on every patient, Dr. Freeman says it is an important and often overlooked measurement. She will frequently add her own heel lifts onto the orthosis as doing so allows her to titrate the height.
Joe DeRose, DPM, emphasizes observation of gait and stance prior to non-weightbearing exams. While the biomechanical exam should be thorough and efficient, Dr. DeRose will focus the exam on things that will change the prescription. For example, if he observes an inverted appearance in RCSP, this may lead to examining the forefoot more carefully. If there is a rigid everted deformity of the forefoot, he says one can prescribe a valgus wedge or reverse Morton’s extension.
Dr. DeRose emphasizes a strong focus on the pathology, including the presenting complaint, deformities such as hallux abductovalgus and leg length discrepancies, and abnormalities in stance and gait. He says this focus allows for better prescription writing and eliminates unnecessary non-weightbearing exams.
Jay Cocheba, DPM, examines subtalar joint range of motion in the frontal plane, looking for both the total range and end range of motion in either direction. As he notes, ascertaining the total range helps identify lapses in symmetry and the amount of correction the patient may tolerate in the heel cup. The end range suggests the amount of rearfoot correction necessary so he can decide on details of that correction, such as posting, shell depth and adjuncts such as skives. At the same time, Dr. Cocheba looks for the amount of arch deformation between NCSP and RCSP, which aids his decision on how much arch fill to add and ideal plate stiffness.
Why is it important to check ankle range of motion?
All three panelists note that one may need a heel lift to accommodate range of motion. Dr. Cocheba often prefers the heel lift to be easily adjustable if he expects an improvement from surgery, physical therapy or a home exercise program.
In addition to adding a small heel lift to accommodate range of motion, Dr. Freeman says one may use a stretching program to normalize ankle function before dispensing the orthosis.
One can observe for early heel off and extensor substitution, and Dr. DeRose says assessing ankle range of motion is a routine non-weightbearing exam that entails checking for a bony block. If there is limited ROM, depending on the amount of pronation available at the subtalar joint, he says the foot will fully compensate by pronating or will partially compensate. One may then observe early heel off, possible knee flexion and abduction of the foot. Given the problematic nature of these effects, Dr. DeRose says podiatrists should address equinus, whether one does so via stretching, heel lifts or orthoses.
“One of the most common reasons for orthosis malfunction is failure to check for inadequate ankle joint range of motion,” asserts Dr. Freeman.
What are the three things I should be looking for before I ship my casts to the lab?
The most important thing Dr. Freeman looks for is whether the negative cast has captured the patient’s forefoot to rearfoot angulation. When casting, she places the negative cast on a flat surface and looks at the heel. Dr. Freeman says the cast should sit everted or inverted by the same number of degrees she measured when evaluating the forefoot to rearfoot relationship. She cites this as an effective method of re-checking the forefoot to rearfoot relationship she previously measured in the biomechanical exam.
Dr. Cocheba wants to see a durable impression with good capture of all contours in the position he desires for a given pathology. For most casts, he says this would mean a “tripod” contact surface with the three lowest points being the heel along with the first and fifth metatarsal heads. For most pathology, his goal in a captured position is to bring the rearfoot to neutral with the forefoot as close to balanced as possible. Dr. Cocheba says this usually requires some dorsiflexion of the hallux. He cannot think of a situation, other than anatomic limitation, in which he would accept a cast with any plantarflexion of the great toe.
Looking at the lateral side of the cast, Dr. Freeman ensures that she has not dorsiflexed the fourth and fifth toes as doing so will create inversion within the forefoot of the cast. Also, when it comes to the lateral side of the negative cast, she notes the lateral arch or calcaneocuboid articulation should form a smooth and gentle angle. If the cast has been supinated, she says the lateral arch will increase in height and the angle will become acute as the forefoot plantarflexes on the rearfoot. If one fabricates an orthosis from a negative cast that was supinated, Dr. Freeman cautions it would be very painful for the patient across the midfoot.
If assistants are the ones who cast, scan or take impressions, Dr. DeRose emphasizes that DPMs should periodically check the quality of the assistants’ work.
“There is a tendency to drift away from good technique until it is fully ingrained,” notes Dr. DeRose.
What is the advantage of casting over other impression techniques?
Plaster casting offers the best control of the midfoot, according to Dr. DeRose. He adds that plaster also allows for casting out supinatus and plantarflexing the first ray. Dr. Freeman agrees. It is easy to lock out the lateral column and cast out supinatus when using plaster, according to Dr. Freeman.
For Dr. Cocheba, plaster casting provides the greatest control over foot position that the cast will reflect. His goal is restoring the foot to a functional position rather than just capturing the dysfunctional position. He also notes that plaster casting is “second to none in accurate, consistent capture of intricate contours.”
Dr. Freeman uses a variety of impression techniques, noting that if she wants to get a good representation of the foot, she will use plaster casting. One of the advantages of using plaster, she explains, is that plaster does not disrupt the soft tissues of the forefoot. She adds that plaster casting gives the best representation of the forefoot to rearfoot relationship. Finally, she says plaster also offers more flexibility when dealing with special situations such as taking a pronated cast.
In regard to other casting methods, Dr. DeRose notes that foam impression techniques have improved. He recommends foam casting with the subtalar joint in neutral, the forefoot to rearfoot perpendicular and cast in the angle of gait.
Dr. DeRose has worked with both laser scanners and digitizers at his lab. He says the biggest problem is positioning the foot well, noting there can be an awkwardness with positioning. Although digital techniques are getting to the point that they rival plaster in accuracy, Dr. Cocheba says the cost still seems prohibitive given the volume of orthoses that most practices prescribe.
What should you be looking for when a patient feels that the orthotic is not functioning correctly?
When there is an issue with the orthosis shell, Dr. Freeman focuses on where on the shell is causing irritation. She frequently finds that medial arch irritation is the result of an orthosis fabricated from a negative cast that was supinated, thus creating an arch profile that is too high. Lateral heel cup irritation is mostly caused by not informing the lab that the patient had a large amount of soft tissue displacement on weightbearing, according to Dr. Freeman. She says posterior heel irritation usually results from asking for a heel cup that is too wide. Dr. Freeman cautions that the deeper the heel cup one orders, the wider the heel cup is and this can lead to shoe fit problems.
Dr. Freeman adds that forefoot irritation, especially in the medial aspect of the forefoot, is frequently the result of too much varus posting in the orthotic. She says varus posting that is too high will not allow the first ray to plantarflex normally during the propulsive phase of gait. Dr. Freeman notes this is frequently the result of having supinated the negative cast.
Dr. DeRose suggests first re-checking that the device fits well when the foot is in a casting position, regardless of the impression technique. After checking how the device sits in the shoe, he says one should then troubleshoot for specific problems such as heel slippage or irritation.
If the problem is with comfort, Dr. Cocheba says the anatomic location of the discomfort usually points to inadequate matching of foot contour, which one must correct before the orthoses can effectively treat the pathology. If the issue is inadequate resolution of symptoms, he considers increasing the amount of correction in the orthoses or adding adjunctive details to optimize functional control. Dr. Cocheba adds that sometimes one must accept a scenario in which other forms of treatment — such as medical, surgical or physical therapy means — will be necessary additions to provide a satisfactory and lasting outcome.
When troubleshooting orthosis issues, Dr. Freeman emphasizes the importance of listening closely to the patient’s complaints before recommending a plan of action. She says some complaints are related to issues of communication, such as if the patient did not follow the recommended break-in regimen, while other complaints stem from shoe accommodation issues. She stresses the point that the orthosis must work with the interface of the shoe.
“The best functional device in the world will not function properly if placed in a floppy heeled or shallow heel countered shoe,” says Dr. Freeman.
Dr. Cocheba is affiliated with Skagit Regional Clinics in Mt. Vernon, Wash. He is a Visiting Professor at Midwestern University and the University of Washington.
Dr. DeRose founded MSI Orthotic Lab. He is an adjunct faculty member at the Arizona School of Podiatric Medicine at Midwestern University.
Dr. Freeman is affiliated with the Arizona School of Podiatric Medicine at Midwestern University. She is an attending physician in the Podiatry Section of the Department of Surgery at the Carl T. Hayden VA Medical Center in Phoenix. She is board certified by the American Board of Podiatric Orthopedics and Primary Podiatric Medicine.