Spasticity is one of the most common neurological impairments, which may occur after an upper motor neuron lesion. It is defined as “disordered sensorimotor control, resulting from an upper motor neuron lesion, presenting as intermittent or sustained involuntary activation of muscle.”1 This usually involves a lesion of both the pyramidal and parapyramidal systems, which may be caused in association with stroke, spinal cord injury, multiple sclerosis, brain trauma, cerebral palsy, or head injury.2 Joints that are affected by spastic muscles may develop deformity, pain, weakness, and abnormal movement.2
Ankle-foot orthoses (AFOs) designed and proposed to influence muscle tone (AFOs with tone-influencing designs) are widely known as “tone-reducing” AFOs, “tone-inhibiting” AFOs, or “dynamic” AFOs (DAFOs). These orthoses were evolved from techniques used in the application of plaster casts for patients with spastic muscle tone. These plaster casts were designed to influence the positive support response or tonic reflex, which had been observed in response to cutaneous stimulation of reflexogenous areas on the plantar surface of the feet in patients with cerebral palsy.3 One of the first attempts in designing such a cast for patients with cerebral palsy was reported by Sussman and Cusik.4 It was followed by a series of subsequent studies on individuals with cerebral palsy.5–10
The theory was then applied to AFO designs. Following the report of their effect on gait in patients with head injury by Zachazewski et al.,11 various AFO designs were proposed and investigated. In their review article, Lohman and Goldstein12 identified four potential tone reduction features, which would be worthy of further investigation. These were a) the addition and location of a metatarsal bar or dome; b) the extent of toe extension induced by the design; c) the amount of loading added to areas adjacent to the Achilles tendon insertion point; and d) the effectiveness of the orthokinetic principles applied in the design.
Although a number of articles on AFOs with tone- influencing designs have been published since then, an up-to-date review of available studies was thought warranted in the recent need of evidence-based practice in orthotic interventions. This article aims to present a concise review of the current state of knowledge to clinicians and researchers by specifically investigating: a) the classification of patient groups recruited into the studies selected; b) the design characteristics of the AFOs used; and c) their clinical effect.
A literature search was conducted using Google Scholar, ISI web of knowledge, Medline, Scopus and RECAL legacy, and a thorough review of cited references from appropriate articles. Key words used were AFO, head injury, cerebral palsy, tone, inhibiting, orthosis, orthotics, reducing, spasticity, spinal cord injury, and stroke. Inclusion criteria for the article of this review article were as follows:
1. Studies were performed on AFOs with tone-influencing designs.
2. AFO designs used in the study were described.
3. Publication of the study was in a peer-reviewed journal in English.
The results of the literature search identified 19 suitable articles (Table 1).11,13–30 These articles were analyzed and compared to produce the following summary.
PATIENT GROUPS RECRUITED IN PREVIOUS STUDIES
Most of the volunteer subjects included in the articles reviewed were children with cerebral palsy,14–16,18,21–23,25–28 although patients with head injury,11,13,15,16 stroke,13,17,19–20,24,30 and spinal cord injury29 were also recruited (Table 2).
The design characteristics of the AFOs with tone- influencing designs used in the reviewed studies are summarized in Table 3. These included nonarticulated AFOs,11,14,15,17,20,21,24,29 articulated AFOs,22,30 supramalleolar orthoses,14,16,18,19,22–23,25–28 and neurophysiological AFOs.13 However, variations were found in certain pertinent AFO design features within these categories.
THE AMOUNT OF EXTENSION OF THE TOES
The majority of studies used orthoses with a toes piece either extended11,15,18,20,22,24,29 or kept horizontal.16,19,21,23,25–28,30 However, the amount of toe elevation or extension varied in the literature. In one study, they were elevated by approximately 10°,18 whereas another recommended their elevation by 0.5 cm.22 A 5-mm-thick boomerang-shaped bar was applied on patients with stroke.24 Zachazewski et al.11 claimed that the toes piece should be hyperextended, whereas Bronkhorst and Lamb15 stated an opposite opinion.
LOADING ON THE METATARSAL HEADS
Although most articles described plaster model rectifications to relieve loading from the metatarsal heads,13,15,16,19–23,25–30 two articles suggested to increase loading on them.11,22 The addition of felt material that extended from under the toes to a more proximal position underneath the metatarsophalangeal joints was believed to help prevent plantar grasping.11 A 0.5 cm of elevation beneath the metatarsal heads was used in an attempt to reduce excessive tone in plantarflexion and inversion.22
ALIGNMENT OF THE ANKLE WITHIN THE AFO
The ankle joint was kept at 90° with the subtalar joint in a neutral position in most AFO designs.11,15,17,20,21 The subtalar joint was again positioned at its neutral position but with free plantar/dorsiflexion ankle movements made available in DAFOs.16,19,23,25–28 Mediolateral ankle stability was useful in providing control of plantar/dorsiflexion in them. The neurophysiological AFOs positioned the subtalar, midfoot, and forefoot to their neutral position and tuned plantar/dorsiflexion ankle movements by the stiffness of the orthoses.13 The ankle joint was kept at 90° with plantarflexion stop and free dorsiflexion in those adopted articulated AFO designs.22,30
LOADING ON THE HEEL
Loading on the heel was relieved in the majority of studies,16,19,21,23,25–28,30 although loading on the heel was augmented in one study assuming that it would assist dorsiflexion of the ankle by increasing cutaneous stimulation of the reflexogenous area.15
LOADING ON THE TENDON INSERTION
Loading was applied medially and laterally to the Achilles tendon insertion area in an attempt to improve contact and afford more rigid immobilization.11,29
The clinical effects of the AFOs reported on temporal and spatial gait parameters, kinetics and kinematics, foot loading, balance, posture, function, and alteration to tone are summarized in Table 4.
Increase in gait velocity17,20,24,29 and in step or stride length,17,20,21,26,29 decrease or increase in cadence,17,20,21,24 reduction in excessive knee flexion,18 improvement in foot loading pattern and support,19,20 improvement in ankle kinematics,11,21 decrease in positive support reflex,11,15 and reduction in time spent in double stance phase29 have all been reported.
BALANCE, POSTURE, AND FUNCTION
Improvement in posture, balance, and standing were reported14,16,25 along with improvement in gross motor functional measures.27
No conclusive neurophysiological effects were reported when walking with the AFOs.26,29,30 Spasticity assessed by studying the median frequency26 and the ratio of maximum Hoffman reflex amplitude to maximum muscle response amplitude30 of electromyography (EMG) signals did not show reductions with the use of such AFOs. However, the mean EMG activity of the gastrocnemius muscle was reported to be better modulated when walking with the AFOs in one study.29
A potential carryover effect was reported in two studies.15,19
COMPARISON WITH STANDARD AFOs
Studies in which comparisons with other types of AFOs were performed did not show conclusive evidence that AFOs with tone-influencing designs were superior to others. Only two studies17,20 showed more positive effects on gait parameters in comparison with standard AFOs, whereas others21,22,26 did not show any significant difference.
This article concisely reviewed the current state of knowledge on the effect of the AFOs with tone-influencing designs. The literature search demonstrated that the relevant studies mainly involved patients with cerebral palsy, followed by those with head injury or stroke. Although spasticity is common among these patient groups, it is not clear which of them would benefit the most from these AFOs.
Marked variations in AFO design parameters were found, such as 1) the type of AFO (i.e., articulated, nonarticulated, supramalleolar, or neurophysiological) used; 2) the amount of toe extension; 3) the amount of loading on metatarsal heads; 4) the amount of loading at the heel; 5) the amount of loading on the Achilles tendon insertion area; and 6) the alignment of an ankle joint. Although more recent studies19,23,25–28 adopted DAFOs whose design characteristics were proposed by Hylton,16 the efficacy of these design parameters requires further investigation.
The AFOs may have positive effect on gait, posture, and EMG data in patients with spasticity. However, it was not conclusive whether they could actually reduce or inhibit muscle tone. Currently, there is no definitive method to quantify spasticity or muscle tone.31,32 This is one of the obstacles in evaluating so-called tone-reducing or tone-inhibiting effects. No significant effect in the median frequency signal26 or Hoffman reflex amplitude30 of the EMG have been reported with the use of such AFOs. The findings of these studies would question their neurophysiological effect. In addition, some studies showed that AFOs with tone-influencing designs did not have any significant effects in comparison with standard AFO designs.21,22,26 Some studies have also suggested that the AFOs may be recommended for use as an adjunct to appropriate physiotherapy, but they might not be effective if they are used alone.16,18,25
On the basis of the results of this literature review, we conclude that the efficacy of the AFOs with tone-influencing designs (i.e., in reducing or inhibiting muscle tone) has not been sufficiently proven because of the very low level of evidence despite the positive clinical effect reported in previous studies. This is because the study design adopted in precedence studies was not robust enough. The articles reviewed showed an equivalent range of level of evidence of Grade C proposed by Sacket.33 Indeed, it is difficult to make a strong argument for a particular position on whether AFOs are able to influence muscle tone when the evidence levels are so low. This is in agreement with previous publications.34,35 Thus, it would not be appropriate to use the term tone-reducing or tone-inhibiting for such AFOs until their efficacy is confirmed with grade A evidence level.33
In summary, the following issues need to be further investigated regarding the use of AFOs with tone-influencing designs:
1. The classification of patient groups that may benefit from these types of AFOs needs to be more accurately defined.
2. The design parameters used in these types of AFOs need to be more quantitatively defined.
3. The statistical and clinically significant effects of these types of AFOs in comparison with standard AFOs need to be demonstrated with randomized controlled trials.
The authors would therefore recommend that future studies should carefully investigate these aspects systematically.
More systematic research with randomized controlled trials is necessary to determine whether AFOs with tone-influencing designs would truly have positive clinical effects. Moreover, it is required to reexamine whether such AFOs do in fact have tone-reducing or tone-inhibiting effects while ambulating. If their positive effects are confirmed in future studies, it will be essential to investigate their optimal designs and to demonstrate which group of patients would benefit the most from the AFOs.
1. Pandyan AD, Gregoric M, Barnes MP, et al. Spasticity: clinical perceptions, neurological realities and meaningful measurement. Disabil Rehabil
2. Barnes MP. An overview of the clinical management of spasticity. In: Barnes MP, Johnson GR, eds. UpperMotor Neuron Syndrome and Spasticity: Clinical Management and Neurophysiology
. Cambridge, UK: Cambridge University Press; 2001:1–11.
3. Duncan WR. Tonic reflexes of the foot. Their orthopaedic significance in normal children and in children with cerebral palsy. J Bone Joint Surg Am
4. Sussman MD, Cusick B. Preliminary report: the role of short-leg, tone-reducing casts as an adjunct to physical therapy of patients with cerebral palsy. Johns Hopkins Med J
5. Duncan WR, Mott DH. Foot reflexes and the use of the “inhibitive cast.” Foot Ankle
6. Mills VM. Electromyographic results of inhibitory splinting. Phys Ther
7. Otis JC, Root L, Kroll MA. Measurement of plantar flexor spasticity during treatment with tone-reducing casts. J Pediatr Orthop
8. Bertoti DB. Effect of short leg casting on ambulation in children with cerebral palsy. Phys Ther
9. Watt J, Sims D, Harckham F, et al. A prospective study of inhibitive casting as an adjunct to physiotherapy for cerebral-palsied children. Dev Med Child Neurol
10. Hinderer KA, Harris SR, Purdy AH, et al. Effects of ‘tone-reducing' vs. standard plaster-casts on gait improvement of children with cerebral palsy. Dev Med Child Neurol
11. Zachazewski JE, Eberle ED, Jefferies M. Effect of tone-inhibiting casts and orthoses on gait. A case report. Phys Ther
12. Lohman M, Goldstein H. Alternative strategies in tone-reducing AFO design. J Prosthet Orthot
13. Ford C, Grotz RC, Shamp JK. The neurophysiological ankle-foot orthosis. Clin Prosthet Orthot
14. Harris SR, Riffle K. Effects of inhibitive ankle-foot orthoses on standing balance in a child with cerebral palsy. A single-subject design. Phys Ther
15. Bronkhorst AJ, Lamb GA. An orthosis to aid in reduction of lower-limb spasticity. Orthot Prosthet
16. Hylton NM. Postural and functional impact of dynamic AFOs and FOs in a pediatric population. J Prothet Orthot
17. Diamond M, Ottenbacher K. Effect of a tone-inhibiting dynamic ankle-foot orthosis on stride characteristics of an adult with hemiparesis. Phys Ther
18. Embrey DG, Yates L, Mott DH. Effects of neuro-developmental treatment and orthoses on knee flexion during gait: a single-subject design. Phys Ther
19. Mueller K, Cornwall M, McPoil T, et al. Effect of a tone-inhibiting dynamic ankle-foot orthosis on the foot-loading pattern of a hemiplegic adult: a preliminary study. J Prothet Orthot
20. Dieli J, Ayyappa E, Hornbeak S. Effect of dynamic AFOs on three hemiplegic adults. J Prothet Orthot
21. Radtka SA, Skinner SR, Dixon DM, et al. A comparison of gait with solid, dynamic, and no ankle-foot orthoses in children with spastic cerebral palsy. Phys Ther
22. Crenshaw S, Herzog R, Castagno P, et al. The efficacy of tone-reducing features in orthotics on the gait of children with spastic diplegic cerebral palsy. J Pediatr Orthop
23. 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
24. Iwata M, Kondo I, Sato Y, et al. An ankle-foot orthosis with inhibitor bar: effect on hemiplegic gait. Arch Phys Med Rehabil
25. Näslund A, Tamm M, Ericsson AK, et al. Dynamic ankle-foot orthoses as a part of treatment in children with spastic diplegia—parents' perceptions. Physiother Res Int
26. Lam WK, Leong JCY, Li YH, et al. Biomechanical and electromyographic evaluation of ankle foot orthosis and dynamic ankle foot orthosis in spastic cerebral palsy. Gait Posture
27. Bjornson KF, Schmale GA, Adamczyk-Foster A, et al. The effect of dynamic ankle foot orthoses on function in children with cerebral palsy. J Pediatr Orthop
28. Näslund A, Sundelin G, Hirschfeld H. Reach performance and postural adjustments during standing in children with severe spastic diplegia using dynamic ankle-foot orthoses. J Rehabil Med
29. 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
30. Ibuki A, Bach T, Rogers D, et al. An investigation of the neurophysiologic effect of tone-reducing AFOs on reflex excitability in subjects with spasticity following stroke while standing. Prosthet Orthot Int
31. Kobayashi T, Leung AK, Akazawa Y, et al. Quantitative measurement of spastic ankle joint stiffness using a manual device: a preliminary study. J Biomech
32. Kobayashi T, Leung AK, Akazawa Y, et al. Evaluating the contribution of a neural component of ankle joint resistive torque in patients with stroke using a manual device. Brain Inj
33. Sackett DL. Rules of evidence and clinical recommendations on use of antithrombotic agents. Chest
34. Bowers R, Ross K. A review of the effectiveness of lower limb orthoses used in cerebral palsy. In: Morris C, Condie D, eds. Recent Developments in Healthcare for Cerebral Palsy: Implications and Opportunities for Orthotics
. Copenhagen, Denmark: International Society for Prosthetics and Orthotics; 2009:235–297.
35. Bowers R. Non-articulated ankle foot orthoses. In: Condie E, ed. Report of a Consensus Conference on the Orthotic management of Stroke Patients
. Copenhagen, Denmark: International Society for Prosthetics and Orthotics; 2004:87–94.
KEY INDEXING TERMS: ankle-foot orthosis; brain injury; tone; muscle; cerebral palsy; spasticity; stroke