Key Insights On Orthotic Casting And Function
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.”