A Guide To Conservative Stabilization Of The Neuromuscular Foot

Given the difficulties of managing neuromuscular conditions in the lower extremity, these authors offer key insights on the use of orthoses, shoe modifications and bracing devices for treating dilemmas ranging from lateral ankle instability to dropfoot.

     The neuromuscular lower extremity presents a variety of challenges for the podiatrist, pedorthist, orthotist and physical therapist. Accordingly, one should have a strong understanding of the role of conservative stabilization for patients who have neurological deviations and deficits that may be caused by a variety of conditions.

     These conditions include Charcot-Marie-Tooth disease, hemiplegic cerebral palsy, spastic diplegia, quadriparesis, peroneal nerve injuries, post-polio syndrome and cerebrovascular accidents.

     It is sometimes difficult to separate and address specific joints when treating the neuromuscular foot as the gait cycle involves closely related interplay among all of the joints of the lower extremity, especially the complex joints of the foot and ankle.1

     When it comes to stabilizing the neuromuscular foot, providers may utilize foot orthoses and shoe modifications as well as bracing devices such as ankle-foot-orthoses (AFO) and knee-ankle-foot-orthoses (KAFO).

     The basic objectives of shoe and bracing treatment in these cases include:

• stabilizing a weak or flaccid foot-ankle complex by compensating for weak muscles or muscle groups;

• correcting passively correctable deformities;

• preventing or slowing the progress of further deformity; and

• regulating or reducing motor tone.

     Essentially, the purpose of treatment is to enhance normal movement while correcting abnormal gait patterns and increasing the efficiency of ambulation.

What You Should Know About Lateral Ankle Instability

Many off-the-shelf options are available for the conservative treatment of mild to moderate ankle instability. Off-the-shelf braces include elastic and nylon lace-up supports as well as pre-molded, plastic, hinged braces. Not only can these braces help prevent unwanted hindfoot and ankle inversion, they allow relatively unrestricted dorsiflexion and plantarflexion of the foot and ankle.

     When it comes to patients with lateral ankle instability, recommended off-the-shelf footwear includes high-top athletic shoes or boots that cover the ankle and provide extra support; cross-trainers or hiking shoes with a stable base and good medial-lateral stability; or neutral or anti-supination walking or running shoes.

     The majority of walking and running shoes are made to prevent overpronation. These anti-pronation shoes often have medial wedging incorporated into the heels as well as extra support and stiffness on the medial side of the shoe. This type of shoe is contraindicated for patients with lateral ankle instability as it will only serve to exacerbate the problem.

     If the off-the-shelf shoe is not sufficient, one can modify it to provide a wider, more stable base of support. 2 Providers can do this by adding a lateral heel flare or outrigger to the sole of the shoe. If this is not sufficient, one can add a lateral buttress or stabilizer. The buttress extends from the floor approximately 4 to 5 inches up the side of the shoe and covers the lateral hindfoot and midfoot. It is made of a stiff material, usually ½ inch to 1 inch thick, and prevents lateral rolling of the hindfoot. One may also reinforce the internal counter of the shoe with fiberglass for added strength and stability.

     One goal of any foot orthosis or AFO is to maintain correct anatomic alignment of the calcaneus in order to reduce hindfoot and ankle medial-lateral instability. This is especially true when dealing with lateral ankle instability. Any sort of AFO will decrease postural sway in stance phase. 3

     The foot orthosis for this condition will typically have a deep heel cup in order to maximize contact with the heel and control of the heel. Often, a lateral heel wedge will be built into the device. For chronic ankle instability, a laterally posted foot orthosis is not usually sufficient and an AFO is required.

     In regard to bracing for ankle instability, one may utilize either a solid AFO or a hinged AFO. If the ankle medial-lateral instability is the primary problem, then a hinged AFO is sufficient. The hinged AFO will prevent motion in the
front while allowing free dorsiflexion and plantarflexion. Appropriate hinged AFOs include: the Richie Brace®, an articulated molded thermoplastic AFO, a metal and thermoplastic hybrid AFO or a metal single or double upright AFO attached to the shoe.

     If the goal is to control motion in more than just frontal plane motion, then one may prescribe a solid ankle molded thermoplastic AFO or Arizona Brace®.

Pertinent Insights On Treating Dropfoot

One basic function of any AFO is to maintain the foot in a plantigrade position. During stance phase, the brace provides a stable base of support and reduces tone. During swing phase, however, the primary function of the AFO is to prevent foot drop.

     There are several devices providers may employ to assist the patient with foot drop. Of course, there are many different styles of braces, both prefabricated and custom-made. There are also other devices such as elastic cords that run from a calf band to the top of the shoe that aid in dorsiflexing the foot. A relatively new development is the emergence of small electrical stimulation devices that send electrical signals that cause the foot and ankle dorsiflexors to fire and lift the foot in swing phase.

     Foot orthoses and shoe modifications alone are inadequate to treat dropfoot. Usually some sort of AFO is indicated.

     A number of manufacturers offer prefabricated carbon fiber composite dropfoot AFOs. These braces are lightweight — with some weighing only a few ounces — and are easily hidden under clothing. One style consists of a thin full-length footplate, a molded calf band and a posterior strut that can be as narrow as 1½ inches. There are also rear-entry models and spiral, wrap around designs. These styles of braces allow for significant heel compression at initial contact, energy return from midstance to terminal stance and toe-off assistance. These benefits allow for a longer and easier stride.

     It is quite common to use thermoplastic leaf spring-style prefabricated AFOs for mild to moderate dropfoot. They are usually available in several sizes and many can be heated and easily modified for a more comfortable fit.

     The posterior leaf spring AFO has a narrow posterior shell. The ankle region trimlines are substantially posterior to the malleoli. The posterior leaf spring AFO does an adequate job compensating for mild to moderately weak ankle dorsiflexors. It provides no medial-lateral control whatsoever. Since this device flexes with every step, it needs to be fabricated from a plastic with good fatigue resistance such as copolymer polypropylene.

     Many off-the-shelf dropfoot AFOs can fit into regular shoes as long as the shoe has some sort of closure system such as laces, a strap and buckle, or Velcro®.

     If there is increased tone, an additional strap at the ankle is required to keep the heel seated snugly in the brace. The shoe alone is not usually sufficient.

     Custom AFOs for dropfoot can fit into two categories: hinged and solid ankle. If there is no increased tone — merely a lack of dorsiflexion strength — then one may utilize a hinged AFO that allows motion. The hinges of either a metal bracing system or a metal-plastic hybrid AFO can either block motion with a pin or assist motion with a spring. Double-action joints stop motion one way and assist it in the opposite direction. There are also semi-flexible plastic hinges with offset tension cables molded inside of them that assist with dorsiflexion.

     If one desires dorsiflexion above neutral, one can set the hinges with a 90-degree plantarflexion stop. This will not assist with toe-off but will prevent foot drop.

     Using hinges that allow the full range of ankle motion but actively assist with dorsiflexion allows the patient without increased tone to walk normally as well as drive a car. Driving a car is certainly possible but more difficult when the patient is wearing an AFO that allows no plantarflexion.

     A full foot plate, molded thermoplastic solid ankle AFO will prevent foot drop and increase propulsion power at toe-off. The same can be said for a custom AFO molded from a pre-impregnated carbon composite. One can fabricate a
single or double upright metal brace to accomplish the same goals. However, it will be bulkier and much more difficult to transfer from shoe-to-shoe.

     When patients have dropfoot and mild lateral ankle instability, as one may sometimes see in patients with Charcot-Marie-Tooth disease, providers can mold a full-length custom foot orthosis — as opposed to a simple liner — into the posterior leaf spring AFO. The foot orthosis should have aggressive lateral posting.

What Are The Benefits Of Tone Reducing And Dynamic AFOs?

Can an orthotic device reduce tone? The proponents of dynamic or tone reducing AFOs maintain that the devices can indeed reduce tone in the foot and ankle. While there is data to support these claims, there are also a number of studies opposing the concept that an AFO can improve function by reducing tone. 4-9

     This debate has been ongoing for years and there is, as of yet, no consensus opinion on the matter. In
general, though, just about all types of AFOs do improve gait function in a spastic foot in comparison with not using an AFO.

     A dynamic AFO is constructed with a very thin, form-fitting, flexible plastic. It permits some ankle motion while maintaining the subtalar joint in a neutral position. This is important as medial-lateral ankle-foot instability is such a common component of spastic equinus. The footplate is uniquely constructed by molded protuberances that apply pressure to specific spots on the sole of the foot. Other features can include a spastic inhibitor bar (an orthotic modification akin to a toe crest), a toe extension plate, toe loops or toe separators, all of which help to keep the toes extended. 10 Specific shapes and placement of metatarsal pads also aid in reducing tone and keeping the toes extended.

     Providers can build these tone-reducing features into a foot orthosis, a solid ankle AFO, a hinged AFO or a supramalleolar orthosis (SMO). The SMO is not as effective as an AFO in preventing plantarflexion as its superior trimlines typically lie just above the medial and lateral malleoli. 11

     As with many other braces, the tone reducing AFO will require the application of an in-depth shoe to accommodate the extra bulk associated with the type of AFO. An in-depth shoe offers extra room in the toe box, typically ¼ inch to 3/8 inch of extra height. It will also have a removable factory insole that one will most likely need to remove to make room for the AFO.

     Depth shoes do not have to be “orthopedic” looking. Many popular commercial athletic shoes are available in multiple wide widths and have removable insoles. 12
Several shoe manufacturers also make dress-type shoes that can be classified as in-depth shoes while still meeting social and cosmetic expectations.

     Another consideration when dealing with the spastic foot is the type of opening on the shoe. The wider and further down the top of the shoe that the opening is, the easier it will be to don and doff.

Can Ground Reaction AFOs Have An Impact?

Clearly, physicians prescribe AFOs for patients with gait deviations of many different types and etiologies. The most obvious effect that AFOs have on the neuromuscular foot is the role they play in compensating for weak dorsiflexors by
preventing foot drop during swing phase. Another sometimes overlooked role of an AFO is to compensate for weak plantarflexors during stance phase. The plantarflexors need to be active during the midstance and terminal stance phases of gait to counter the ground reaction force that work to dorsiflex the ankle.

     While all designs of rigid AFOs will provide some degree of ground reaction, there is a specific AFO design known as a ground reaction AFO that achieves this function more effectively and comfortably in cases in which providing ground reaction is the primary purpose of the device.

     The ground reaction AFO is a rigid, fixed ankle device. It is made with the ankle at neutral. The upper portion of the brace wraps around the anterior proximal tibia. The footplate is rigid as well and runs the full length of the foot. These features halt the forward advancement of the tibia and force the knee into extension. It is useful in preventing unwanted ankle dorsiflexion and knee extension like one might see in a patient with a crouch gait.

     This brace is contraindicated when a knee flexion contracture or a dynamic knee flexion deformity is present. This brace often works well for patients with weak quadriceps and hip extensors. 13 The ground reaction AFO will require some sort of depth shoe to accommodate the full-length rigid foot plate.

In Conclusion

Shoes, shoe modifications and orthoses all play important roles in stabilizing the neuromuscular foot. One can use them to compensate for neurological deficits such as weak muscles or muscle groups. While these modalities will not correct fixed deformities, they can, in certain instances, prevent or delay the formation of a fixed deformity. They can also assist in providing more efficient, easier and more natural ambulation while improving balance and stability. 14

     The best possible care for the neuromuscular foot requires a multidisciplinary approach with input from a team of physicians including a podiatrist, orthotist, pedorthist and physical therapist.

     Dennis Janisse, CPed, is a Clinical Assistant Professor in the Department of Physical Medicine and Rehabilitation at the Medical College of Wisconsin and is also the Pedorthic Consultant for Foot Clinics at the Milwaukee County Medical Complex. He is the President and CEO of National Pedorthic Services, Inc.

     Erick Janisse, CPed, CO, is the Vice President of National Pedorthic Services, Inc.

References:

1. Lin SS, Sabharwal S, Bibbo C. Orthotic and bracing principles in neuromuscular foot and ankle problems. Foot Ankle Clin. 2000 Jun; 5(2):235-64. 2. Marzano R. Fabricating Shoe Modifications and Foot Orthoses. In: Janisse, DJ (ed). Introduction to Pedorthics, Columbia: PFA, 1998 3. Baier M, Hopf T. Ankle orthoses effect on single-limb standing balance in athletes with functional ankle instability. Arch Phys Med Rehabil. 1998 Aug; 79(8):939-44. 4. Romkes J, Brunner R. Comparison of a dynamic and a hinged ankle-foot orthosis by gait analysis in patients with hemiplegic cerebral palsy. Gait Posture. 2002 Feb; 15(1):18-24 5. Zachazowski JE, Everle ED, Jeffries M. Effects of tone-inhibiting cast and orthoses on gait. Phys Ther. 1982; 62(4):453-5. 6. Sussman MD, Cusick B. Preliminary report: role of short leg, tone-reducing casts as adjunct to physical therapy of patients with cerebral palsy. Johns Hopkins Med J. 1979; 145:112-4. 7. Cherry DB, Weigand GM. Plaster drop-out casts as a dynamic means to reduce muscle contracture. Phys Ther. 1981; 61:1601-3. 8. Lohman M, Goldstein, H. Alternative strategies in tone-reducing AFO design. JPO. 1993; 5(1):1-4. 9. Nash B, Roller JM, Parker MG. The effects of tone-reducing orthotics on walking of an individual after incomplete spinal cord injury. J Neurol Phys Ther. 2008 Mar; 32(1):39-47. 10. Iwata M, et al. An ankle-foot orthosis with inhibitor bar: effect on hemiplegic gait. Arch Phys Med Rehabil. 2003 Jun; 84(6):924-7. 11. Molnar GE. Orthotic Management of Children. In: Redford J, Basmajian J, Trautman P (eds.) Orthotics: Clinical Practice and Rehabilitation Technology. Kansas City: Churchill Livingstone, 1995 12. Frey C. Shoes. In: Goldberg B, Hsu J, (eds.) Atlas of Orthoses and Assistive Devices, 3rd Ed. St. Louis: Mosby, 1997 13. Yang GW, Chu DS. Floor reaction orthosis: clinical experience. Orthotics and Prosthetics 1986; 40(1):33-37. 14. Pohl M, Mehrholz J. Immediate effects of an individually designed functional ankle-foot orthosis on stance and gait in hemiparetic patients. Clin Rehabil. 2006 Apr; 20(4):324-30.