CMTnyc Adaptive Therapy and Bracing in CMT

Orthoses and Adaptive Equipment in Neuromuscular Disorders
by Barry Rodstein and Dennis D.J. Kim

Reprinted from Motor Disorders, edited by David S. Younger, MD, Chapter 39.

An orthosis is a device, such as a brace or splint, that is applied externally to the body. It modifies the functional and structural characteristics of the neuromuscular and musculoskeletal systems. The term orthotic is a term that refers to the study and practice of bracing, not to the actual device. Adaptive devices are external appliances, including orthoses, canes, crutches, walkers, reachers, and wheelchairs, that are used to improve function.

The management of neuromuscular disorders changes continuously because of significant medical and technologic advances, including those in molecular biology, genetics, and immunology. This has resulted in more precise diagnoses, superior care, and increased lengths of survival. Thus, there are more patients with neuromuscular diseases, some elderly, requiring adaptive equipment and orthoses, and it is prudent for physicians involved in their care to be familiar with these. This chapter reviews the basic approach to bracing in neuromuscular disease.

An orthosis is named for the joint that the brace crosses, beginning proximally, followed by the word orthosis. The general term "foot" is used for joints distal to the ankle. Thus, a brace that begins at the leg, crosses the ankle, and ends at the foot is referred to as an ankle-foot orthosis (AFO). If the brace begins at the thigh, crosses the knee and ankle, and ends at the foot, it is called a knee-ankle-foot orthosis (KAFO). Many specific braces are referred to by nonstandard names base on their function, design, or where they were developed: reciprocating gait orthosis, patella tendon-bearing AFO (PTB AFO), and University of California at Berkeley Laboratories Foot Orthosis are such examples.

The exact purpose of a brace and its goal should be obvious to a patient; otherwise, it will not be used. A common pitfall in our zeal to fix the patient and normalize gait is to overbrace, resulting in orthoses that are unnecessarily awkward or too heavy to use. A useful approach is to begin with the simplest brace that is likely to result in safe and functional ambulation and use a more cumbersome one only when necessary. This is particularly true for KAFOs and longer braces, in which the weight of the brace is an important consideration.

Often, control is achieved at one joint by moving or controlling adjacent ones. This usually requires that the adjacent joints are either functional or able to be braced. The most common example is control of the knee with an AFO, which requires intact hip musculature, particularly extensor muscles. Knee buckling can be prevented by the combination of a dorsiflexion stop at the ankle and active hip extension, so that a KAFO is not needed.

An essential concept in bracing is that forces are applied to at least three points. Two of them, applied to one side of the limb or body part, stabilizes it, whereas the third exerts the necessary counterforce in between them. The magnitude of the counterforce equals the sum of the opposing forces (1).

For orthoses that involve the foot, such as the KAFO or AFO, the shoe is an integral part of the system even if it is not an actual part of the orthosis because the throat or the, portion anterior to the tongue is a necessary point to the three point system and the one that exerts the most force. Other areas along which forces are applied are the metatarsal heads through the sole of the shoe or a footplate and the upper calf by means of a proximal band. As a rule, a shoe without a wide padded area and firm closures, such as penny loafers and pumps and those with elastic laces, should not be used with a brace. An orthosis with a footplate inside the shoe can be used with standard shoes, ideally with removable insoles that can be taken out to accommodate the orthosis. If this is not possible, a shoe one-half size longer or wider may suffice. Patients unable to tie standard laces should have looped Velcro closures with a D-ring. Footwear can have an impact on the dynamic response of the orthosis because even minor changes in heel design and height, sole material, or angle of the toe spring can affect the biomechanics of walking. Decisions and instructions regarding footwear should be made with the orthosis in mind.

Orthoses of the leg can exert significant pressure on the skin. When the primary function of an orthosis is to control movement of a joint, pressure and shear forces will be inversely proportional to the length of the lever arm and the area over which force is applied. To minimize undue pressure on the skin, force should be applied as far as possible from the fulcrum using the longest possible lever arm, and the area of contact should be maximized. The type of orthosis and the materials used should be carefully chosen for insensate or obese patients and in those with significant edema along the area to be braced. Whenever possible, forces should be applied by a tubular or closed structure producing the equivalent of a thin-walled pressure vessel, in which the resulting hydrostatic forces provide considerably greater resistance to torsional stress, allowing the use of thinner materials as compared with an open design (2,3). Examples are the circumferential designs of the thigh enclosure in a KAFO and most spinal orthoses.

Patients with useful motion in a joint should have braces designed to allow this motion, For example, allowing useful dorsiflexion will improve gait, especially at late stance phase. This approach aids in preserving and improving range of movement, particularly in the triceps surae because weight bearing in the lengthened position provides useful muscle stretching. Standing by means of a tilt table or a standing frame is one of the best ways to improve range of motion (ROM) at the ankles in patients unable to ambulate (2). Resting night splints assist in preventing contractures; however, the knee should be in extension to stretch the gastrocnemii and soleus muscles. ROM maintenance should be instituted early and aggressively because correction of contractures is much more difficult than prevention, if not impossible.

Whenever possible, it is important to design braces to accommodate the anticipated changes that occur as a result of progressive neuromuscular disease. For example, when choosing an AFO, an articulating ankle with adjustable dorsiflexion and plantar flexion is better than one with a fixed ankle. Any patient, but particularly those with waxing and waning diseases such as multiple sclerosis, are prone to discard braces that are no longer used and should be reminded not to do so.

Orthoses were first made of leather, fabric, and metal and attached directly to shoes. Polypropylene and other modern plastics are now preferred by patients because they offer better control through closer fit and decrease energy expenditure due to lighter weight. In addition, they are more cosmetically appealing. They are of two types: thermoplastic and thermosetting plastic. Thermoplastic orthoses can be repeatedly remolded by reheating. Thermosetting plastics are liquid resins at room temperature and harden when set. They are applied to mesh laminates under vacuum pressure to form the composite material. Although they are more durable, high-temperature thermoplastics such as polypropylene are suitable for many bracing needs and are sometimes chosen because of their lower cost and ease of modification. Thermoplastic orthoses can be reinforced with composite inserts, but they do not become an integral part of the brace and are thus not as strong as the laminated ones (4). Thermosetting plastics are superior in cases of high stress, such as in weight transfer, PTB AFO, and obesity. Laminated braces are lighter, stronger, and more versatile. Because lower forces are required for upper extremity and temporary lower extremity bracing, lower temperature thermoplastics such as polyethylene are generally acceptable; they are also easier to modify. For short-term use on sensate patients, prefabricated braces are often appropriate but should not be considered in cases of significant sensory impairment, edema, foot deformity, or obesity.

The prime goal of pediatric orthotics is to prevent deformity; however, when one already exists, efforts should be aimed at correcting it. When that is not possible, the orthosis should be designed to accommodate the deformity. Children should be seen for frequent brace adjustments during growth spurts because of changes in girth and height and contours of the ankle and calf portions.

Several factors are important to increase acceptance of braces in children. First, the brace should be comfortable. This usually requires use of a soft lining or padding. Second, there should be parental acceptance of the brace. Parents should be educated in its use and purpose and in differentiating pain due to poor fit from annoyance due to the confinement imposed by the brace. The ease of donning and doffing also increases patient use and parental acceptance of the brace. Bright colors, patterns, buttons, buckles, and cartoon characters can make the brace more cosmetically appealing.

AFOs are versatile, relatively inexpensive, and cosmetically inoffensive. They are the most commonly used lower extremity orthoses. Table I lists the major types of AFOS, their biomechanical functions, conditions in which they are deemed appropriate, and particular advantages and disadvantages.

This prototypical AFO (Fig. 1) consists of hinge joints connected proximally to steel, aluminum, or titanium uprights. A posterior calf band with an anterior strap fixes the uprights to the leg, and a stirrup fixes the brace distally to the shoe. A split stirrup can be removed to allow for its use in different shoes, which must be modified by attaching a caliper box to accept the stirrup. A light, thin, and durable solid stirrup can be riveted directly to the shoe and should be used in patients with severe spasticity; in weight transfer AFOs (5), as for example, a PTB AFO; in those who tamper with their braces. A variation on the double-upright AFO is a custom-made footplate, which is placed inside the shoe, which should have adequate room to accommodate, such as extra depth shoes and sturdy sneakers with removable insoles.

As with other AFOS, the upper margin of the calf band must end at least 2 to 3 cm below the fibular head to avoid injury of the peroneal nerve. The ankle should be aligned with the lateral orthotic joint slightly anterior to the lateral malleolus, and the medial joint should be slightly posterior to the medial malleolus. The joints can have a single posterior channel or both posterior and anterior channels. Pins or springs can be placed in these channels and adjusted to limit or assist motion as necessary. Commonly used configurations include a single long-length posterior channel that provides a dorsiflexion assist with a spring or a plantar flexion stop with a pin, or dual channels that in addition provide a dorsiflexion stop. These joints are easily adjusted by turning a screw to vary the allowable motion or amount of assist. The Klenzak joint is widely used and has a particularly long posterior channel to accommodate a long spring that enables effective dorsiflexion assist. A brace can be configured to provide plantar flexion assist, but there are few clinical applications for this, and the dorsal aspect of the foot does not tolerate any substantial pressure.

Modifications can be made to this type of brace to address a wide variety of conditions. A T- or Y-strap can be used to control pronation or supinatiop. For excessive pronation, the strap is attached to the medial side of the shoe and buckled around the lateral upright to produce a force directing the subtalar joint inward; the opposite configuration can be used to control supination.

Although extremely versatile and effective, traditional -double-upright AFOs are used much less because of the advancement of modern synthetic thermoplastics and composite materials. The double-upright AFO is still the ideal choice for patients with severe spasticity, an insensate foot, fluctuating edema, or a severe foot deformity requiring a custom-molded shoe. In addition, patients who have been using this type of brace for many years may not wish to change. In developing countries, the technology for plastic braces may not be available, making the double-upright brace the default choice.

The spring-wire AFO (Fig. 2) is a variation on the double-upright AFO in which the heavy uprights are replaced with stainless steel wires coiled at the ankle to provide a spring action that assists dorsiflexion. Like the double upright AFO, the distal end is attached directly to an orthopedic shoe, which can accommodate edema and allow shoe modifications. It has the advantages of being lighter in weight, less conspicuous, and providing better dorsiflexion assistance. However, neither varus-valgus control nor plantar-dorsiflexion stops are possible, and, like the double-upright AFO, replacement of the shoe requires an orthotist. This brace is used primarily for isolated dorsiflexion weakness when a plantar leaf spring ankle-foot orthosis (PLSO) cannot be used due to edema, loss of sensation, ulcers, or advanced deformity of the foot requiring shoe modifications.

One modification that makes this brace lighter is a single upright and joint on the AFO instead of two. This provides control and assist in the sagittat plane but does not prevent internal or external rotation of the leg. The single joint is subject to significant torsional stress and is less durable unless an extra-heavy joint is used, negating the decrease in weight. Thus, single upright AFO are usually not indicated and infrequently prescribed.

This simple lightweight metal brace clips onto the back of a shoe and provides dorsiflexion assist. Although inexpensive, it requires a sturdy orthopedic shoe to be effective and shifting of the posterior upright on the calf can be problematic for some patients. The PLSO has largely superseded the Veterans Administration Prosthetic Center t)race. Which is now primarily used as a trial dorsiflexionassist brace in the clinic setting.