Home > Newsletters and Journals > JACPOC 1991 Vol 26, Num 2 > pp. 65

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Dynamic Dorsiflexion Assist Polypropylene Ankle Foot Orthosis

The need for a new design in polypropylene AFO's-one that included the functions of dynamic dorsiflexion assist and limited motion stops was presented to our firm.

Therefore, we set out to design an appliance made from all-plastic components which would be worn inside the shoe. Success was achieved with a lightweight, multi-functional, cosmetic, all-plastic AFO which needs minimum maintenance and gives the patient, physician, and therapist the desired functions without the cumbersome, high maintenance traits of the conventional metal AFO.

The double bar metal AFO with dorsiflexion assist (Klenzac) is a very functional design and can be used for a variety of ankle foot problems. One can choose from free ankle motion, with or without dorsiflexion assist, or limited motion of any degree with the use of a double action type joint.

Major drawbacks with this system include high maintenance, noise from the metal joints and wear and tear on clothing, furniture and floors.

As this orthosis requires attachment externally to the shoe, it is unsightly and provides little cosmesis for the wearer. The excessive bulk and weight of heavy-duty steel joints, which are common in this style of appliance, are undesirable.

The development of polypropylene in orthotics was a blessing for both adult and pediatric AFO wearers. The features of a polypropylene orthosis include: minimum maintenance, lightweight, good cosmesis (when worn inside the shoe no additional shoe work is required).

The main disadvantage is the foot is kept in a fixed position, providing contraindication to many ankle foot treatment practices.

Recently, several suppliers of ankle joints, including the Gillette and Gaffney systems, have been filling a need by offering the orthotist a choice in their designs of dynamic or articulated AFO's by the inclusion of an ankle joint.

With the need for dynamic dorsiflexion assist and some simple limited motion features, that could be easily adjusted by the therapist and orthotist, a polypropylene AFO satisfying these criteria was designed (Fig. 1 ).

The design consists of a conventional articulated AFO utilizing Gillette hinges. On the posterior aspect of the upper section, a cylinder is incorporated containing a spring which acts on a polypropylene piston-rod entering on the foot section. The spring tension within the cylinder then moves the heel section of the AFO distally, putting the forefoot into dorsiflexion.

With this design, the AFO may require an ankle strap to keep the heel secure within the AFO and prevent pistoning of the leg within the orthosis.

A plaster mold is prepared for vacuum forming in the conventional manner with joint brackets in place.

A piece of I cm polypropylene is prepared to the size of 12 cm by 21/2 cm and is heated with the polypropylene sheet in the oven.

The placement of the cylinder piece is outlined on the mold at the flattened area over the achilles tendon area. After sufficient heating of the plastic, the small piece is placed in the area marked and the rest of the AFO is then vacuum formed in the conventional manner. The small plastic piece will, if sufficiently heated, fuse to the dropped polypropylene (Fig. 2 ).

Practice will be necessary in this technique as speedy team work is important to provide the necessary fusion of the two polypropylene pieces.

After cooling, the trim lines may be drawn and the AFO can be cut off the mold (Fig. 3 ). After removal from the plaster mold, the foot and calf sections are separated, by using a bandsaw, at the cutting line indicated with masking tape.

A 17/64"drill bit is then used to carefully drill a hole into the centre of cylinder piece. This hole will be drilled to within 11/2 cm from the top of the cylinder. It will later accept a spring, plantarflexion stop pin and the plastic rod, acting as a piston.

The alignment of the hole on the top cylinder now has to be transferred down to the foot piece for precise alignment. This second hole will only be 1 cm deep and will receive the piston rod.

After assembly and insertion of the spring and proper length piston rod the orthosis is ready for fitting.

Fitting is done in the conventional manner with a static fitting to check the fit and comfort and to establish the final trim lines. As well, a dynamic fit is done to see the patient weightbear and walk.

At this point, the spring tension may need adjusting and this can be accomplished by adjusting the length of the spring and the piston rod. The aim is to achieve a clean dynamic action from heel contact to toe off. Our model has a tension adjustment screw added for easier adjustment of the spring tension proximal to the spring on the cylinder (Fig. 1 ).

If a plantarflexion stop is required, simply place a pin of the appropriate length within the spring, or utilize polystyrene in the conventional way.

This orthosis can be prescribed for night use in either pre/post-surgical heel cord tightness to stretch the heel cord and allow a greater range of motion into dorsiflexion.

The space requirements of this design are the same as those for conventional polypropylene AFO's and therefore offers patients a greater selection of shoe wear, rather than the limited choices available when utilizing the Klenzac type AFO.

When limited dorsiflexion is required, this can be accomplished by adding one webbing strip vertically onto each side of the cylinder. These strips are fastened with rivets onto the foot section and extend to the calf section posteriorly (Fig. 4 ).

For smaller children and patients with Cerebral Palsy, the therapist may wish to adjust the degree of dorsiflexion stop in order to reduce tone. In these situations a metal plate can be added with pre-drilled holes in the cylinder. The piston rod has a slot added proximally and a screw at this point will act as a dorsiflexion stop. The screw can then be moved easily to change the degree of motion with each hole equal to approximately 3 degrees.

Results

Ninety patients (seventy children and twenty adults) have been fitted with the dorsiflexion assist AFO since the first prototype was developed in September 1990. This includes unilateral and bilateral cases.

To date there have been few problems with the device. No breakage has occurred nor has any follow up servicing been required.

With the use of plastics, the need for lubrication, as with the Klenzac type, has been eliminated. In addition, overall cosmesis has not been compromised, with noise and clothing wear kept to a minimum.

These experiences also hold true for adult wearers, as we have several very active adult clients who are wearing the orthosis on a daily basis and have not experienced any difficulties with the design.

This design has provided us with a reliable orthosis offering the many desired functions of a Klenzac without the associated problems.

Ford Laboratories, #106-11400 Bridgeport Road, Richmond, BC V6X 1T2