Orthotics Currently Being Used

Existing Orthosis

There have been many different designs for an Ankle Foot Orthosis (AFO). However, the model most currently used is still a basic mold made out of polypropylene or metal-alloy made to fit the ankle of the patient (Figure 1).

There are three major objectives for the design of any orthosis:
1. Restoration of normal function and ability
   i. control of motion
   ii. correction of deformity
   iii. compensation for weakness
2. Make it as comfortable to wear as possible
3. Minimize the abnormal appearance of the orthosis

Most advanced AFOs have not been able to improve on all three objectives from the basic AFO.

Basic Ankle Foot Orthosis (AFO)

Currently, the clinician must choose between metal alloy-based devices, plastic-based devices, and a hybrid assembly incorporating both materials. In most cases, this choice is left to the orthotist and patient. Figure 1 shows the standard polypropylene AFO, which completely immobilizes the ankle while providing stability. This AFO makes the patient have to adapt their walking style and usually means having an abnormal walk and higher stresses at the joints.

Figure 1 Standard Ankle Foot Orthosis (AFO)

Advanced Ankle Foot Orthosis

Figure 2 Hybrid AFO combining the intimate, secure fit of molded plastic shell with the ease of adjustment of metal double action ankle joints (Michael 2000)

There are multiple designs of AFOs depending on the pathology of the individual.

One of the most common lower limb deficits is a flaccid equinus, which results in lack of dorsiflexion. To compensate for pretibial compartment weakness there are several orthotic options.

For more complicated cases, such as rigid deformities, only selected cases can be treated. The AFO shown in Figure 2 helped to improve the deformity of the lower leg caused by spastic contractures of the plantar flexors.

This AFO option matrix summarizes the motion control options available at the ankle and provides examples of both metal and plastic AFOs that offer such function (Michael 2000).

Dorsiflexion Assist Controlled by Spring
Ankle-Foot Orthosis (DACS-AFO)

Figure 3 Lateral view of the DACS-AFO
A front view can be seen by clicking the picture

The DACS-AFO, seen in Figure 3, consists of body and sole portions, which are made from polypropylene and are connected with two joints and a cylinder. The cylinder generates a dorsiflexion-assist moment with an angle of plantar flexion at heel strike (Hachisuka 1998).

Unfortunately, no significant difference was found between the DACS-AFO and a basic AFO and most subjects of their study preferred their old AFO.