Posts Tagged AFO Mechanics
SureStep manufactures a variety of products but is primarily known for the SMO (Supra malleolar orthosis) and pediatric AFOs (ankle foot orthosis). The SureStep SMO is meant for patients up to 80 pounds with hypotonic presentations. The purpose is to control the side to side movements of the ankle. The trim lines can be extended longer laterally or medially depending on whether the patient is pronating or supinating. As patients grow older there is a device called the Big Shot that accommodate children and adults weighing over 80 pounds. What makes the SureStep SMO so unique is the dynamic function that the brace allows. It uses compression to create alignment, unique trim-lines to allow freedom of motion where needed, and made from a material that travels together along with the foot.
Controling the Tri-Planar Deformities
This works under compression to maintain stability through midline. In young patients with CMT they can possibly present with a more over pronated foot position because of the low muscle tone (hypotonia) prior to developing a high arch foot presentation. This can been seen in CMT patients who have some symptoms of the disease but have not developed a high arch otherwise known as pes cavus foot. The SMO holds the heel in vertical alignment, giving stability in a coronal plane (side to side) position. An SMO is not necessarily for a patient who has weaknesses pushing up or down the ankle, just poor side-to-side movement.
Improving Stability During Gait
The device is designed to allow for motion to still occur from in and out of the midline position but limits the extremes that the foot would go to, in other words the extreme rolling inward our outward of the ankle. The goal is to improve balance and stability, or limit orthopedic injury. This helps limit out toeing or in toeing as well by improving the position to foot is landing on the ground. Having improved alignment may also utilize remaining strength for dorsiflexion or plantarflexion because the line of pull that these muscles are in has improved line of progression.
Fitting the Device
The trim-lines of the SureStep SMO are designed to be either longer on the lateral border for pronation or medial border for patient who supinate excessively and the orthotist should make the appropriate selection based on the patient’s mechanics. These trim-lines are critical to the successful outcome of this device. Although the SureStep SMO is primarily designed for a younger population as children get older or adults who still have need for such a device the same mechanism of function can be accomplished using the BigShot SMO manufactured by SureStep.
Composite material advances over the past 10 years have improved the design creativity and possibility for clinical orthotists worldwide. In the past, an ankle orthosis required a completely solid and fully encompassing design in order to attain the mechanical control, durability and ultimately the function needed for corrective ankle varus bracing. These devices were essentially plastic shells that created a solid/static environment which was safer than not using a brace at all, but they were also highly problematic with patients complaining of pressure points and a clunky gait. Today we can simulate more natural gait patterns while completely avoiding pressure points.
Controlling the Tri-Planar Deformities
Kinetic Research offers a variety of ankle braces, each with its own character and effect to meet the needs of the user, from the most basic needs to the most complex. For folks that have foot/ankle weakness but have good alignment of their ankle, we offer the Noodle line of AFOs. These are the most dynamic and least restrictive designs for controlling drop foot. When the user has a tight heel cord with mild supination or ankle varus, they become a candidate for a PLS design. When the user has more significant ankle varus he/she becomes a candidate for the ValgaNoodle AFO. The ValgaNoodle offers the highest degree of lateral control that we can provide. It’s important to have a team approach when choosing the type of AFO that will work best for your individual needs, and there is always a trade off between control and mobility. The team is made up of the patient, the orthotist and the physician/therapist, and all have to be involved for the best results. The objective is to “put on as little as possible, but get the job done”.
Improving Stability During Gait
The ValgaNoodle is made specifically for varus control. It’s a highly custom AFO, meaning. That it is not assembled using pre-made components. The creation of a ValgaNoodle begins with a highly skilled orthotist who will evaluate and cast for the device. That attending orthotist will manipulate and control the patient’s foot while he is casting, keeping the ankle in the best position possible to maximize the effect of the finished ValgaNoodle. Evaluations and observations made by the clinical orthotist are then incorporated into a design formulation that will work best for the individual patient. The design details are then determined based on the level of control vs free movement that is needed to maximize the performance of the user. One of the objectives is to keep the ValgaNoodle lightweight and as simple to use as possible. The orthotist will select the device based on the severity of the case, as well as the users lifestyle, activities and footwear.
Fitting the Device
The one common mechanical concept for the ValgaNoodle variations of AFOs is, that they will all have a single medial strut with a floating lateral “reverse T” cuff.
Design options for the footplate:
- Flat, in which we match the bottom of the shoe. When we make it in this format, it will usually have a custom foam removable arch support. It offers the least control but because it’s flat, we can make it flexible.
- Contoured. This is similar to a UCBL footplate. Our technicians will adjust the cast taken by your orthotist to increase lateral control in a compact way for easy shoe selection.
- Contoured with high control. This system goes higher than the UCBL, encompassing the dorsum of the foot, and has a special 3-point strapping system to provide maximum control.
Design options for the strut:
- Solid ankle, the highest level of control, removing the user’s ability to dorsi/plantar flex.
- Dynamic, which allows dorsi/plantar flexion, but with reduced lateral control.
Design options for the cuff:
- Posterior, for a normal or hyperextended knee.
- Anterior, generally used for knee extension weakness. Easier to don, but limited to low top shoes.