Plastic Ankle-Foot Orthoses

These are the most common AFO's today. They provide an intimate fit and are lightweight, washable cost-effective, and relatively cosmetic. A one-piece plastic AFO does not have a true joint, but the amount of ankle motion can be controlled by modifying the ankle trim line, thickness, and properties of the plastic. The footplate usually ends just proximal to the metatarsal heads and are f sometimes referred to as '/4 footplates. Although a full footplate improves push off, is more difficult to don and doff, and increases the risk of breakdown, they are indicated in conditions associated with excessive toe flexor tone or flexion contractures of the toes but are infrequently used in adults. A hybrid can be made combining a plastic shoe insert and hinged joint with either a plastic calf shell or a metal upright attached to a calf band.

Plantar Leave Spring Ankle-Foot Orthoses

This widely used lightweight plastic AFO is made of high-temperature thermoplastic polypropylene (Fig. 3). It is lightweight, inexpensive, relatively easy to fabricate, washable, cosmetically benign, and allows for ease in exchange of footwear. The degree of trimming and thickness of the material determines the amount of spring action and thus dorsiflexion assist and the amount of mediolateral control. It can be used for almost all conditions involving flaccid dorsiflexor weakness but is less well suited for resisting plantar flexion as, for example, in upper motor neuron (UMN) disorders with excessive spasticity or if there is substantial mediolateral ankle instability. In those situations, an articulated or less flexible brace is preferable. Dorsiflexion can be easily restored by a PLSO for complete foot drop due to peroneal palsy, lumbosacral root or plexus lesion, or cornpartment syndrome. The primary function of this brace is control of the swing phase of walking and therefore needs only to support the weight of the foot and shoe, approximately 2 pounds (6). When a patient has dorsiflexion and plantar flexion weakness, such as in a sciatic nerve injury, a dorsiflexion-assist AFO can satisfy the needs for daily walking activities, particularly in geriatric patients, whose gait pattern may not demand strong push off. (FIG. 3.) Flantar leaf spring ankle-toot orthosis, made with polypropylene.

Semisolid and Solid Ankle-Foot Orthoses

In this AFO, the trim lines of the calf shell are brought somewhat more anterior than in the PLSO. This results in increased resistance to plantar flexion and dorsiflexion and increased control of mediolaterat motion. If the trim lines are brought further anterior to surround the ankle, there is minimal ankle motion and the brace is then referred to as a solid AFO (Fig. 4). Solid and semisolid AFOs are more durable than articulated AFOS. Gait difficulties may arise with these braces or in other circumstances that result in further diminished ankle ROM, Although not yet in common use, designs are beginning to appear in which polyethylene is added to allow more flexibility, and a horizontal slit is made posteriorly to allow sagittal motion. Such a design may allow for a very lightweight dorsiflexion-assist brace, function ally similar to a PLSO but providing better medial-lateral control.

Articulating Plastic Ankle-Foot Orthoses

These braces use hinged joints attached to plastic proximal and distat components (Fig. 5). In many ways, they combine the advantages of both double-upright and solid AFOs and are the second most common type of lower extremity orthoses. They are probably the most commonly prescribed AFO in patients with spasticity. Like double-upright AFOS, various configurations allow for combinations of plantar and dorsiflexion stops and mild dorsiflexion assist. They are lightweight, relatively cosmetic, and quite versatile. Because of the solid footplate and mediolateral stability they provide, they can control the subtalar joint and thus facilitate appropriate stretching of the triceps surae and Achilles tendon.

However, compared with nonarticulating AFOS, they are considerably more expensive and less durable, and their joints and attachments are under higher stress and therefore more prone to excessive wear and early failure. Thus, when very high forces are expected as for example with obesity or very high tone, a solid AFO is still preferable.

Spiral and Hemispiral Ankle-Foot Orthoses

The spiral and hemispiral AFOs were designed to permit the natural internal and external rotation of the leg with respect to the foot while controlling ankle and subtalar motion. This theoretic advantage over other AFO is offset by material fatigue and difficulty initially and subsequently maintaining proper fit. The hypothetical advantage of allowing physiologic tibial rotation and subtalar motion may not actually occur due to the footplate of the brace that restricts subtalar motion. These AFO are not in widespread use (7).

Patellar Tendon-bearing Ankle-Foot Orthoses

This particular solid AFO is designed with a snug-fitting bivalved calf portion to partially relieve distal weight bearing by distributing weight to the medial tibial condyle, patellar tendon, and the soft tissues of the leg. They are useful in patients with foot ulcers, tibia] fractures, painful heel conditions, avasculay necrosis of the ankle or foot, and Charcot joints, It should usually be custom-made to optimize weight distribution. A rockerbottom and ankle reinforcements are often incorporated to minimize ankle movement and active push off (8). The PTB AFO is usually contraindicated in patients with vascular insufficiency because of the high forces distributed along the popliteal artery (9). In this instance, a solid ankle-anterior shell AFOS, with rocker-bottom sole to prevent significant motion from the ankle to the midfoot and Plastazote lining, should be used instead.

Knee-Ankle-Foot Orthoses

These should be prescribed with discretion, such as when it is necessary to control the knee directly, when an AFO or another indirect intervention is not adequate, or when the ankle or foot must be suspended or controlled. Impaired proprioception at the knee may necessitate bracing proximal to the calf; however, if only knee control alone is necessary, a knee orthosis (KO) may be the better choice. KAFO are used in rheumatoid and other generalized arthritides to stabilize the joints, especially since weakness is usually not the main problem and the weight of the braces is less important. They are also used in patients with poliomyelitis and the post-polio syndrome (PPS) wherein the nature of the paralysis is spotty, there is no spasticity, and sensation is intact. Many patients with poliomyelitis have been successfully managed with KAFO for several decades. Bracing for t NIN conditions is usually more complex and difficult to achieve than in flaccid conditions because of poor trunk balance and central motor control and the frequent presence of ataxia, apraxia, involuntary movements, and spasticity (10). While obstacles can often be overcome by an AFO, the problems are compounded with KAFO, and thus their use in UMN conditions is rarely beneficial.

Alternatives to Knee-Ankle-Foot Orthoses

Less-cumbersome solutions should be considered before prescribing a KAFO. Knee buckling, for example, can be addressed by using an AFO with the ankle fixed in 5 to 10' of plantar flexion, thereby increasing the knee extension moment and assisting the weakened quadriceps. This may reduce the risk of falling and obviate or delay the need for KAFO. One problem with this approach is that genu recurvatum may result in excessive strain on the knee capsule and ligaments. In addition, as with patients using KAFO to ambulate, weak proximal lower extremity or trunk muscles may limit lifting of the limbs or trunk sufficiently to clear the feet for swing-to or swing-through gait. When further control of the knee is necessary, an AFO can be used with a temporary KO in anticipation of partial quadriceps recovery or while the patient is being trained in a more secure gait pattern. Diabetic plexopathy truncal radiculopathy, diabetic amyotrophy, and acute inflammatory demyelinating polyneuropathy are diseases wherein ultimate improvement can occur and in which an AFO and temporary KO may be appropriate.

Design Considerations

Distally, the design of a K-AFO is essentially the same as an AFO and uses the various types of plastic or metal designs described in the previous section. To this is added a thigh band or plastic shell with intervening hinges that can limit or lock motion. In some designs, the joint is offset so that in early stance it is posterior to the ground reaction force, thereby creating an extension moment that increases knee stability. The proximal thigh band should end about I to 2 cm below the ischial tuberosity with the patient standing (6). When knee flexion is particularly difficult to control, an anterior prepatellar band can be added. If a significant change in condition is expected, an adjustable joint should be used. When locking knee joints are used, the patient has to unlock the knee to sit.

With the changing axis of rotation of an anatomic knee joint, the fixed-axis mechanical joint will not move completely in unison with the knee resulting in shifting of the orthosis with knee flexion and extension and discomfort. Polycentric knees are designed to minimize this discrepancy but are only needed when a significant amount of knee motion will occur during ambulation. Because patients requiring KAFO will generally not ambulate with a great amount of knee motion, polycentric joints are usually not necessary and are more commonly used in athletic KOs.

Ambulation with Bilateral Knee-Ankle-Foot Orthoses

Most patients with bilateral weakness who require KAFO to ambulate find that the effort of donning and doffing them, the weight of the braces, and the energy expenditure of walking with both knees locked all preclude functional ambulation; in fact, it would be difficult for many healthy individuals without impairments. Patients with paraplegia resulting from complete spinal cord injuries were reported to consume 500% more oxygen per meter when ambulating with bilateral KAFO and crutches than normal subjects. Furthermore, their speed of walking is 29 m/min compared with 80 m/min in normal subjects (6). Patients will often plead fervently for KAFO and are quite genuine in their belief that they will use them to ambulate; however, functional or even regular therapeutic ambulation is rare. The exception is in patients with poliomyelitis or young, vigorous, and highly motivated patients who choose to ambulate despite the fact that wheelchair mobility is faster and more efficient. Bilateral KAFO should not be prescribed, particularly when one considers their cost, unless there is a strong indication that they will be used in daily activities.

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Fig. 3. Plantar leaf spring ankle-foot orthosis, made with polypropylene.

FIG. 4. Solid ankle-foot orthosis with instep strap, made with laminated plastic.

FIG. 5. Articulating ankle-foot orthosis with instep strap, made with laminated plastic.