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Neurophysiologic Orthotic Designs in the Treatment of Central Nervous System Disorders

Joanne Kiope Shamp, C.P.O., M.A.

The orthotic management of pathologic gait patterns associated with lower limb spasticity has undergone a renaissance. It began in the late 1960s with the introduction of thermoplastic molded orthoses and the design possibilities afforded by total contact. ^1,2 As neurophysiological approaches were developed to include tone-reducing casts and temporary splints from low-temperature plastics, the implication to orthotic practice became clear.^3,4,5,6,7 By 1982, Eberle et al. had reported success with an inhibitive AFO that "allows for all of the tone-inhibiting characteristics of casting . . . to be built into the AFO. "⁸ The biomechanical and total contact features of plastic orthoses had been enhanced by the emergence of neurophysiological handling techniques. The result was a markedly improved function for the patient with a central nervous system disorder.

Clinic teams that utilize a neurophysiological approach believe that "spasticity is reduced by working against these spastic patterns" and that new learning can be achieved by the patient that will provide improved range of motion and increased control of balance reactions.⁹ Orthotic devices are an integral part of the neurophysiological treatment plan. By providing a stable base, the therapist can direct attention to the proximal structures with regard to static and dynamic alignment and weight shifting for walking.

The characteristics and design of the optimum orthosis in the presence of spasticity are as intricate and variable as spasticity itself, necessitating the use of custom devices precisely fabricated for the biomechanical and neurophysiological needs of the individual patient. The list of orthotic techniques available to address a patient's specific goals and/or needs must be carefully utilized in the planning stages of orthotic care.

Rationale for Orthotic Techniques

There is considerable evidence in the literature supporting claims that tone can be influenced by cutaneous stimulation and joint position. This may be a combination of reflex reaction and of changes to the patient's ability to appropriately sequence muscle activity beginning at the ankle first.

"Investigation has demonstrated that superficial cutaneous stimulation of the plantar metatarsal region of the foot in patients who have suffered cerebral insult will cause tonic contraction of the plantarflexors of the foot and digits including the triceps surae and hamstrings."¹⁰ This is observed clinically when "in attempting to stand, the spastic child touches the ground with his foot and exerts pressure on the foot within the reflexogenic area of the positive supporting reaction. He is prevented from putting his heel to the ground by an upsurge of extensor spasticity which produces the well-known pattern of extension, inward rotation and adduction of the whole of the standing leg, with plantarflexion of the foot.""

The sensitivity of the reflex activity to po sition is a major factor in efforts to modify reflex hypertonicity by means of an orthosis. "These reflexes are deployed in such a man-ncr that they are capable of reacting to for-ward (toe grasp), backward (dorsiflexion), lateral (eversion) and medial (inversion) displacement of the center of gravity of the upright body. Habitual reflex-inducted deformities of the foot may become fixed, and proximal contracting musculature may hecome hypertonic creating balance problems."¹²

The concern expressed by Horak and Shumway-Cook¹³regarding consideration of sequencing "strategies" as a major underly mg cause for characteristics typical to a hemiplegic gait are supported by Nashner et al. "Activation of the anterior tibialis and quadriceps muscles, antagonists which helped to brake the sway movement, were sequenced in the non-involved leg beginning at the base of support and then radiating upward, while the reverse sequence of antagonist activation was observed in muscles of the spastic leg."

Identification of areas for the potential influence of neurologic function in the presence of spasticity can lead the orthotist to techniques that combine biomechanical principle with neurophysiologic input within a single orthotic design.

Orthotic Techniques

Clinical evaluation of the goals and needs of a specific patient provides the basis for the selection of all orthotic techniques available to bridge the gap between observed function and normal gait (Table 1) .

Prescription Rationale

Orthotic techniques selected may be incorporated into a variety of custom molded orthoses. Factors influencing the type of orthosis prescribed for the control of lower limb spasticity include the degree of spasticity with associated gait abnormalities, strength and range of motion, sensory "awareness" and functional goals.

Degree of Spasticity

Quantitative assessment of spasticity is a necessary but purely subjected action on the part of the orthotist. "There are no accurate objective means for the accurate measurement of the degree of spasticity in our present armamentarium. Thus far, clinical evaluation remains the most reliable method."¹⁵

Lehneis classified spasticity as minimal, moderate or severe in terms of function of the foot and ankle during gait. ¹⁶ Shamp et al. described use of the classifications in their clinical observation: "Minimal spasticity allows the patient to land on a stable calcaneus without excessive supination of the forefoot and then shift the body weight over the heads of the metatarsals, although during swing phase the foot assumes a varus or supinated posture. Moderate spasticity causes the calcaneus to assume a position of varus with excessive supination at initial contact; however, during midstance, some pronation occurs and body weight can again be transferred normally across the forefoot. Severe spasticity is characterized by the foot and ankle being held in a position of equinus throughout the stance so that the body weight remains on the lateral aspect of the forefoot with little or no weightbearing through the heel or medial metatarsal heads. This varus position persists throughout swing phase also."¹⁷

Strength and Range of Motions

The clinical evaluation of muscle strength and joint range of motion is made difficult by the presence of spasticity and the associated mass patterns of movement. While some literature has discussed the merits of evaluation and casting in the prone position, "it has been demonstrated experimentally that in the hemiparetic patient a muscle's strength response often is sensitive to the body position . . . . Hence, to identify the causative mechanism for a gait deviation, the muscles must be tested with the patient standing and walking."^18,19 Perry concludes that " . . one cannot lay these patients on an examining table for close testing of the factor which might be contributing to a problem identifled when the patient was upright. Instead, the examination must be conducted with the patient upright. "21)

it is a functional overview of muscle and joint activity, combined with passive testing in an upright position, that will be most useful in the prescription of an orthotic design. Manual testing in the sitting position with alterations of joint positions will yield insight into passive range of motions and joint position-muscle strength interactions.

Sensory Awareness

The orthotist should be cognizant of the presence of one-sided neglect, visual/perceptual disabilities and communication disorders in regard to the overall safety and stability of the spastic patient. He should also bear in mind that tone will increase with fear of falling, emotional disturbances and general excitation.²¹ The orthosis prescribed must allow for safe function with the anticipated fluctuations in spasticity as well as provide assistance for alterations in joint proprioception

Orthotic Designs

Multiple variations of three basic designs of foot and ankle-foot orthoses have been utilized for the control of lower limb spasticity: custom plantar foot orthoses and UCBLmodified designs, the neurophysiological AFO, and hinged ankle joint AFO designs.²²

Group One: Foot Orthoses and UCBL-Modified Designs
Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8

Indications:

1. Mild to moderate spasticity.
2. Ability to achieve heelstrike in stance phase.
3. Need for reduction of hypertonic foot reflex activity.

Contraindications:

1. Fixed equinus or reflexogenic foot deformity.
2. Patient refusal to wear low-heeled, lace or VelcroŽ closure shoes.
3. Inability to maintain follow-up by clinic team on a scheduled (minimum biannual) basis.

Fabrication Method: Vacuum-formed over positive model of corrected foot or foot-ankle. Polypropylene with optional plastazote for plantar foot orthoses, copolymer or polyethylene for UCBL-modified FO and AFO designs.

Trimline Variations: Mild hypertonic foot reflex activity including mild toe-clawing in the presence of stable subtalar and ankle joints can be managed with a plantar FO. Presence of mild spasticity and non-neutral subtalar joint is an indication for an UCBL style AFO with plastic extended to include the medial and lateral malleoli. Presence of mild to moderate spasticity with mild instability and non-neutral subtalar and ankle joints in stance phase will require prescription of UCBL-modified AFO design with medial and lateral extensions to mid-calf. Optional strap configurations may be used for control of mild swing phase abnormalities, i.e., posterior proximal calf strap for plantarflexion resistance.

Group Two: Neurophysiological AFO
(Figure 9 and Figure 10 )

A thorough discussion of this non-hinged, flexible AFO design first described by Shamp, Ford and Grotz is found in Clinical Prosthetics and Orthotics, Volume 10, No.1, pp.15-23. Indications:

1. Minimal to moderate spasticity.
2. Normal passive range of dorsiflexion with knee in flexion.
3. Stable weight and lack of significant volume instability secondary to edema.
4. Minimal to moderate varus instability of subtalar joint.
5. Need for reduction of hypertonic foot reflex activity.

Contraindications:

1. Fixed equinus deformity.
2. Patient refusal to wear low-heeled lace or Velcro closure shoes.
3. Inability to maintain follow-up with clinic team (minimum bi-annual).
4. Early excessive pronation or calcaneal valgus in stance phase.

Fabrication Method: Vacuum-formed over positive model of corrected leg below the knee. Polypropylene (3/16") with corrugations and partial plastazote (1/8") liner. Trimline Variations: Narrowing of footplate under midfoot for increased flexibility in presence of adequately facilitated straight plane dorsiflexion.

Group Three: Hinged AFO Designs
Figure 11 , Figure 12 , Figure 13 , Figure 14 , Figure 15 , Figure 16 , Figure 17 , Figure 18 , Figure 19 , Figure 20 , Figure 21 , Figure 22 , Figure 23 , Figure 24

Indications:

1. Moderate to severe spasticity.
2. Early flaccidity following CVA or Closed Head Injury (CHI).
3. Presence in stance phase of equinus with valgus or varus of subtalar joint.
4. Need for variable orthosis for early onset-neurophysiologic treatment plan.
5. Expectation of functional increase or decrease secondary to recovery or a progressive disorder, i.e., multiple sclerosis.
6. Need for biomechanical input of floor reactions to knee (variable).

Contraindications: Excess equinovarus fixed deformity that cannot be functionally compensated for with posting or heel wedges.

Fabrication Method: Vacuum-formed over modified positive model of leg below the knee. Calf section molded first of polypropylene (1/8" or 3/16"). Calf section trimmed to desired size and placed on cast prior to second molding for foot section. Plaster "ramp" over Achilles tendon created prior to footplate molding will allow for trim to dorsiflextion assist-plantarflexion resist function (Figure 26 ) if desired at present or later date. Footplate molded of polypropylene, copolymer or high density polyethylene dependent upon flexibility and strength requirements.

Trimline Variations: This "Progressive Neurophysiological AFO" will allow for the early use of a custom AFO with the potential for continuous functional change throughout the recovery and treatment following a cerebral vascular accident or closed head injury. The AFO can be used in a full range of functions as follows:

1. Solid ankle AFO (Figure 11 and Figure 12 ).
2. Plantar flexion stop with limited to full dorsiflexion range of motion (Figure 13) .
3. Dorsiflexion assist with plantarflexion resist (Figure 14) .
4. Free dorsiflexion-plantar flexion (Figure 15) .
5. Plantar flexion stop-free dorsiflexion ((Figure 16) . The design has been used with excellent results in the treatment of cerebral palsy and other spastic pediatric disorders where the clinic team expects new learning and increased function with neurophysiologic training. Any stage of the AFO design may be used as the permanent design. See case studies:
   Figure 17 , Figure 18 , Figure 19 , Figure 20 , Figure 21 , Figure 22 , Figure 23 , Figure 24

Casting Technique

"The casting technique is similar to that described in Lower Limb Orthotics A Manual, and is a procedure commonly used by certified orthotists."^23,24 A circumferential wrap cast is applied with the patient in a seated position with knee flexed and hip flexed and adducted for tone reduction. A child may be more relaxed if casted while seated on the draped lap of a parent. The orthotist must be familiar with the optimal points of cutaneus stimulation and effectively use finger placement during the casting procedure to reduce hypertonic reflex activity (Figure 25) .

Occasionally the patient may have a tone-reducing footplate that has been effective in the neurophysiologic treatment plan. This footplate can be used against the plantar surface of the foot in the casting procedure so that removal and pouring of the positive model will reproduce the footplate contours (Figure 26) .

Modification of the Positive Model

Precise modification of the positive model is essential to accomplishing the desired neurophysiological and biomechanical goals (Table I) . Plaster removal and additions are performed in designated areas to a depth of 0.5 to 1 cm. dependent upon the compressibility of the patient's extremity and the amount of force necessary to create the desired three-point pressure system or to influence neurologic activity. The removal and addition of plaster (Table 2) is followed by smoothing of the positive model prior to vacuum-forming with plastic. Further information on cast modification can be found in "The Neurophysiological Ankle-Foot Orthosis," Clinical Prosthetics and Orthotics, Volume 10, No.1, pp.15-23.

Fabrication

One layer of PerlonŽ and a ladies knee-high stocking are applied to the positive model to create adequate vacuum for drape-forming and to leave a smooth inner surface on the finished orthosis. These layers are smoothed evenly with talc. The stress-relieved plastic chosen is drape-formed under vacuum to the positive model and allowed to cool for 24 hours prior to removal with a cast saw and sanding to the desired trimline configurations.

When a second molding will be performed for a hinged overlap style Progressive NP-AFO, a layer of PerlonŽ and stocking is again used over the trimmed calf section and cast prior to drape-forming of the foot section

Clinical Experience

The NP-AFO, Progressive Hinged NPAFO and UCBL-modified FO and AFO designs have been prescribed for over 400 patients with central nervous system disorders since this work began in 1984. There has been overwhelming acceptance due to the improved functions, comfort, cosmesis and lightweight character of these designs.

The clinic team has found significant advantages with these specialized designs. Patients who previously wore other plastic or metal orthoses are progressing beyond their prior functional levels with a decreased use of assistive devices such as canes and walkers. Patients report increased speed and acceptance in their children along with greater ease of play up and down from floors, chairs and other elevations. Several patients who previously wore KAFOs are functioning successfully with AFOs.

Summary

A combination of biomechanical and neurophysiological principles have been utilized in the design of custom orthoses for the treatment of spasticity in the lower limb. These designs are characterized by total contact pressures selected to inhibit and/or facilitate hypertonic reflex activity while allowing all freedoms of joint motion possible. In combination with neurophysiologic treatment plans by the entire clinic team, the NPAFO, Progressive Hinged NP-AFO and UCBL-modified designs have resulted in significant functional gains and decreased functional hypertonicity in patients with central nervous system disorders.

Acknowledgements

The author wishes to acknowledge and thank the physicians, physical and occupational therapists, and other professionals of the Akron area for the mutual respect and progressive attitudes that have led to the high quality of clinic team care available in Northeast Ohio. Acknowledgement is also given to Robert Grotz, M.D. and Cyndi Ford, P.T., as well as Enrique Canilang, M.D., and Michael Delahanty, M.D., for their encouragement and assistance in the development of the neurophysiological and/or progressive neurophysiological AFO designs.

Joanne Klope Shamp, C.P.O., M.A. is with the Shamp Prosthetic-Orthotic Center in Norton, Ohio.

References:

1. Yates, G., "A Method for Provision of Lightweight Aesthetic Orthopaedic Appliances," Orthopaedics, 1968, pp.153-162.
2. Lehneis, H.R., "New Concepts in Lower Extremity Orthotics," Medical Clinics of North America, 53(3), 1969, pp. 585-592.
3. Bobath, K., "A Neurophysiologic Basis for the Treatment of Cerebral Palsy," 2nd Edit., Spastics International Medical Publications, London, 1980.
4. Duncan, W. and D. Mott, "Foot Reflexes and the Use of the Inhibitive Cast," Foot and Ankle, 1983.
5. Sussman, M. and B. Cusick, "Preliminary Report: The Role of Short Leg, Tone-Reducing Casts as an Adjunct to Physical Therapy of Patients with Cerebral Palsy," Johns Hopkins Medical Journal, 145(3), 1979, pp.112-114
6. Bobath, K., "The Problem of Spasticity in the Treatment of Patients With Lesions of the Upper Motor Neuron," The Western Cerebral Palsy Centre, London.
7. Utley, J., NDT Adult Hemiplegia and Closed Head Injury Certification Course, Columbus, Ohio, July 1982.
8. Eberle, E.D., M. Jeffries and J.E. zewski, "Effect of Tone-Inhibiting Casts and Orthoses on Gait: A Case Report," Physical Therapy, 62(4), 1982, pp. 453-455.
9. Bobath, B., "Treatment of Adult Hemiplegia," Physiotherapy, 63(10), October 1977, pp. 310-311.
10. Jordan, R.P., "Therapeutic Considerations of the Feet and Lower Extremities in the Cerebral Palsied Child," Clinics in Podiatry, 1(3), Decemher 1984, pp.551-552.
11. Bobath, K., A Neurophysiologic Basis for the Treatment of Cerebral Palsy, 2nd Edit., Spastics International Medical Publications, 1980, p.44.
12. Duncan and Mott, "Foot Reflexes and The Use of the Inhibitive Cast," p.145.
13. Horak, F.B. and A. Shumway-Cook, Instructional Syllabus, "New Perspectives on Balance and Coordination: Neurophysiological Basis for Evaluation and Treatment," 1989.
14. Nashner, L.M. et al., "Stance Posture Control in Select Groups of Children with Cerebral Palsy: Deficits in Sensory Organization and Muscular Coordination," Experimental Brain Research, 49, 1983, p. 397.
15. Westin, G.W. and S. Dye, "Conservative Management of Cerebral Palsy in the Growing Child," Foot and Ankle, 4(3), 1983.
16. Sarno, J.E. and H.R. Lehneis, "Below-Knee Orthoses: A System for Prescription," Archives of Physical Medicine and Rehabilitation, 54, December 1975, p. 548.
17. Shamp et al., "The Neurophysiological Ankle-Foot Orthosis," Clinical Prosthetics and Orthotics, 10(1), pp.15-23.
18. Langer Biomechanics Group, Instructions for Casting for the T.R.A.F.O., 1011 Grand Blvd., Deer Park, N.Y.
19. Perry, J. et al., "The Determinants of Muscle Action in the Hemiparetic Lower Extremity (And Their Effect on the Examination Procedure)," Clinical Orthopaedics and Related Research, 131, March-April 1978, p.78.
20. Ibid., p.88.
21. Bobath, "A Neurophysiologic Basis for the Treatment of Cerebral Palsy," p.310.
22. Shamp et al., "The Neurophysical Ankle- Foot Orthosis," pp.15-23.
23. Lower Limb Orthotics: A Manual, 1st Edit., Rehabilitation Engineering Center, Moss Rehabilitation Hospital, Philadelphia, 1978.
24. Shamp et al., "The Neurophysical Ankle-Foot Orthosis," p.19.
25. Perry et al., "The Determinants of Muscle Action in the Hemiparetic Lower Extremity," p. 86.
26. Shamp et al., "The Neurophysical Ankle-Foot Orthosis," p.18.