Design and Effect of Ankle-Foot Orthoses Proposed toInfluence Muscle Tone: A ReviewToshiki Kobayashi, PhD, Aaron K.L. Leung, PhD, Stephen W. Hutchins, PhD

ABSTRACTAnkle-foot orthoses (AFOs) designed and proposed to influence muscle tone are generally called as “tone-reducing” AFOs,“tone-inhibiting” AFOs, or “dynamic” AFOs. These orthoses were originally evolved from the use of plaster casts toinfluence the positive support reflex or tonic reflex, which were either triggered by pressing reflexogenous areas on theplantar surface of the foot or suppressed by offloading them. The effects of wearing AFOs to influence muscle tone havemainly been studied in patients with cerebral palsy, stroke, or head injury. Although different AFO designs exist, it seemsthat there is a lack of evidence to demonstrate that these AFOs can actually reduce or inhibit spastic muscle tone. Thisarticle specifically reviews the classification of patient groups recruited in previous studies, the design characteristics ofAFOs, and the clinical and biomechanical effects reported. The results of this review suggested that the level of evidencefor AFOs being able to influence muscle tone was very low. Therefore, further research with randomized controlled trialsis required to investigate their clinical effects. (J Prosthet Orthot. 2011;23:52–57.)

KEY INDEXING TERMS: ankle-foot orthosis, brain injury, tone, muscle, cerebral palsy, spasticity, stroke

S pasticity is one of the most common neurologicalimpairments, which may occur after an upper motorneuron lesion. It is defined as “disordered sensorimo-

tor control, resulting from an upper motor neuron lesion,presenting as intermittent or sustained involuntary activa-tion of muscle.”1 This usually involves a lesion of both thepyramidal and parapyramidal systems, which may be causedin association with stroke, spinal cord injury, multiple scle-rosis, brain trauma, cerebral palsy, or head injury.2 Jointsthat are affected by spastic muscles may develop deformity,pain, weakness, and abnormal movement.2

Ankle-foot orthoses (AFOs) designed and proposed to in-fluence muscle tone (AFOs with tone-influencing designs) arewidely known as “tone-reducing” AFOs, “tone-inhibiting”AFOs, or “dynamic” AFOs (DAFOs). These orthoses wereevolved from techniques used in the application of plastercasts for patients with spastic muscle tone. These plastercasts were designed to influence the positive support re-sponse or tonic reflex, which had been observed in response

to cutaneous stimulation of reflexogenous areas on the plan-tar surface of the feet in patients with cerebral palsy.3 One ofthe first attempts in designing such a cast for patients withcerebral palsy was reported by Sussman and Cusik.4 It wasfollowed by a series of subsequent studies on individuals withcerebral palsy.5–10

The theory was then applied to AFO designs. Following thereport of their effect on gait in patients with head injury byZachazewski et al.,11 various AFO designs were proposed andinvestigated. In their review article, Lohman and Goldstein12

identified four potential tone reduction features, which wouldbe worthy of further investigation. These were a) the additionand location of a metatarsal bar or dome; b) the extent of toeextension induced by the design; c) the amount of loadingadded to areas adjacent to the Achilles tendon insertion point;and d) the effectiveness of the orthokinetic principles appliedin 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 inthe recent need of evidence-based practice in orthotic inter-ventions. This article aims to present a concise review of thecurrent state of knowledge to clinicians and researchers byspecifically investigating: a) the classification of patientgroups recruited into the studies selected; b) the designcharacteristics of the AFOs used; and c) their clinical effect.

METHODSA literature search was conducted using Google Scholar,

ISI web of knowledge, Medline, Scopus and RECAL legacy,and a thorough review of cited references from appropriatearticles. Key words used were AFO, head injury, cerebralpalsy, tone, inhibiting, orthosis, orthotics, reducing, spastic-ity, spinal cord injury, and stroke. Inclusion criteria for thearticle of this review article were as follows:

TOSHIKI KOBAYASHI, PhD, is affiliated with the Orthocare Inno-vations, Mountlake Terrace, Washington.

AARON K.L. LEUNG, PhD, is affiliated with the Department ofHealth Technology and Informatics, The Hong Kong PolytechnicUniversity, Hong Kong, People’s Republic of China.

STEPHEN W. HUTCHINS, PhD, is affiliated with the Centre forHealth, Sport and Rehabilitation Sciences Research, University ofSalford, Salford, United Kingdom.

Disclosure: The authors declare no conflict of interest.

This work was supported by The Hong Kong Polytechnic UniversityInternational Postgraduate Scholarships for PhD studies.

Copyright © 2011 American Academy of Orthotists and Prosthetists.

Correspondence to: Toshiki Kobayashi, PhD, 6405 218th SW,Suite 301, Mountlake Terrace, WA 98043; e-mail: tkobayashi@orthocareinnovations.com

52 Volume 23 • Number 2 • 2011

1. Studies were performed on AFOs with tone-influencingdesigns.

2. AFO designs used in the study were described.3. Publication of the study was in a peer-reviewed journal

in English.

RESULTSThe results of the literature search identified 19 suitable

articles (Table 1).11,13–30 These articles were analyzed andcompared to produce the following summary.

PATIENT GROUPS RECRUITED IN PREVIOUSSTUDIES

Most of the volunteer subjects included in the articles re-viewed were children with cerebral palsy,14–16,18,21–23,25–28 al-though patients with head injury,11,13,15,16 stroke,13,17,19–20,24,30

and spinal cord injury29 were also recruited (Table 2).

DESIGN CHARACTERISTICSThe design characteristics of the AFOs with tone-

influencing designs used in the reviewed studies are sum-marized in Table 3. These included nonarticulatedAFOs,11,14,15,17,20,21,24,29 articulated AFOs,22,30 supramal-leolar orthoses,14,16,18,19,22–23,25–28 and neurophysiologicalAFOs.13 However, variations were found in certain perti-nent AFO design features within these categories.

THE AMOUNT OF EXTENSION OF THE TOESThe 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 approximately10°,18 whereas another recommended their elevation by 0.5cm.22 A 5-mm-thick boomerang-shaped bar was applied onpatients with stroke.24 Zachazewski et al.11 claimed that the toespiece should be hyperextended, whereas Bronkhorst and Lamb15

stated an opposite opinion.

LOADING ON THE METATARSAL HEADSAlthough 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 Theaddition of felt material that extended from under the toes toa more proximal position underneath the metatarsophalan-geal joints was believed to help prevent plantar grasping.11 A0.5 cm of elevation beneath the metatarsal heads was used inan attempt to reduce excessive tone in plantarflexion andinversion.22

ALIGNMENT OF THE ANKLE WITHIN THE AFOThe ankle joint was kept at 90° with the subtalar joint in

a neutral position in most AFO designs.11,15,17,20,21 The sub-talar joint was again positioned at its neutral position butwith free plantar/dorsiflexion ankle movements made avail-able in DAFOs.16,19,23,25–28 Mediolateral ankle stability wasuseful in providing control of plantar/dorsiflexion in them.The neurophysiological AFOs positioned the subtalar, mid-foot, and forefoot to their neutral position and tuned plantar/dorsiflexion ankle movements by the stiffness of the ortho-ses.13 The ankle joint was kept at 90° with plantarflexion stopand free dorsiflexion in those adopted articulated AFOdesigns.22,30

LOADING ON THE HEELLoading on the heel was relieved in the majority of stud-

ies,16,19,21,23,25–28,30 although loading on the heel wasaugmented in one study assuming that it would assist dorsi-

Table 1. Articles identified in the literature search

References Year

Zachazewski et al.11 1982Ford et al.13 1986Harris and Riffle14 1986Bronkhorst and Lamb15 1987Hylton16 1989Diamond and Ottenbacher17 1990Embrey et al.18 1990Mueller et al.19 1992Dieli et al.20 1997Radtka et al.21 1997Crenshaw et al.22 2000Romkes and Brunner23 2002Iwata et al.24 2003Näslund et al.25 2003Lam et al.26 2005Bjornson et al.27 2006Näslund et al.28 2007Nash et al.29 2008Ibuki et al.30 2010

Table 2. Classification of patient groups recruited in previousstudy

Patientgroup References

Cerebralpalsy

Harris and Rieffle14; Bronkhorst and Lam15;Hylton16; Embrey et al.18; Radtka et al.21;Crenshaw et al.22; Romkes andBrunner23; Näslund et al.25; Lam et al.26;Bjornson et al.27; Näslund et al.28

Head injury Zachazewski et al.11; Ford et al.13;Bronkhorst and Lamb15; Hylton16

Stroke Ford et al.13; Diamond and Ottenbacher17;Mueller et al.19; Dieli et al.20; Iwata etal.24; Ibuki et al.30

Spinal cordinjury

Nash et al.29

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flexion of the ankle by increasing cutaneous stimulation ofthe reflexogenous area.15

LOADING ON THE TENDON INSERTIONLoading was applied medially and laterally to the Achilles

tendon insertion area in an attempt to improve contact andafford more rigid immobilization.11,29

CLINICAL EFFECTSThe 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 sum-marized in Table 4.

GAITIncrease 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 footloading pattern and support,19,20 improvement in ankle ki-nematics,11,21 decrease in positive support reflex,11,15 andreduction in time spent in double stance phase29 have allbeen reported.

BALANCE, POSTURE, AND FUNCTIONImprovement in posture, balance, and standing were re-

ported14,16,25 along with improvement in gross motor func-tional measures.27

Table 3. Design characteristics of AFOs with tone-influencing designs

AFO designs References

AFO typeNAAFO Zachazewski et al.11; Harris and Rieffle14; Bronkhurst and Lamb15; Diamond and Ottenbacher17;

Dieli et al.20; Radtka et al.21; Iwata et al.24; Nash et al.29

AAFO Crenshaw et al.22; Ibuki et al.30

SMO Harris and Rieffle14; Hylton16; Embrey et al.18; Mueller et al.19; Crenshaw et al.22; Romkes andBrunner23; Näslund et al.25; Lam et al.26; Bjornson et al.27; Näslund et al.28

NAFO Ford et al.13

Toe extensorExtended Zachazewski et al.11; Bronhorst and Lamb15; Embrey et al.18; Dieli et al.20; Crenshaw et al.22;

Iwata et al.24; Nash et al.29

Horizontal Hylton16; Mueller et al.19; Radtka et al.21; Romkes and Brunner23; Näslund et al.25; Lam et al.26;Bjornson et al.27; Näslund et al.28; Ibuki et al.30

Metatarsal headLoaded Zachazewski et al.11; Crenshaw et al.22

Unloaded Ford et al.13; Bronkhorst and Lamb15; Hylton16; Mueller et al.19; Dieli et al.20; Radtka et al.21;Crenshaw et al.22; Romkes and Brunner23; Näslund et al.25; Lam et al.26; Bjornson et al.27;Näslund et al.28; Nash et al.29; Ibuki et al.30

Ankle alignment90° with subtalar neutral Zachazewski et al.11; Bronhorst and Lamb15; Diamond and Ottenbacher17; Dieli et al.20; Radtka

et al.21

Free PF/DF with subtalarneutral

Hylton16; Mueller et al.19; Romkes and Brunner23; Näslund et al.25; Lam et al.26; Bjornson etal.27; Näslund et al.28

PF/DF with sutalar,midfoot, forefootneutral

Ford et al.13

Free DF with 90° PF stop Crenshaw et al.22; Ibuki et al.30

Medial-lateral stability Hylton16; Embrey et al.18; Mueller et al.19; Romkes and Brunner23; Näslund et al.25; Lam etal.26; Bjornson et al.27; Näslund et al.28

HeelLoaded Bronkhurst and Lam15

Unloaded Hylton16; Mueller et al.19; Radtka et al.21; Romkes and Brunner23; Näslund et al.25; Lam et al.26;Bjornson et al.27; Näslund et al.28; Ibuki et al.30

Tendon insertionLoaded Zachazewski et al.11; Nash et al.29

Hylton’s design (DAFO) Hylton16; Mueller et al.19; Romkes and Brunner23; Näslund et al.25; Lam et al.26; Bjornson etal.27; Näslund et al.28

AFO, ankle-foot orthosis; AAFO, articulated ankle-foot orthosis; DAFO, dynamic ankle-foot orthosis; DF, dorsiflexion; NAAFO, nonarticulated ankle-footorthosis; NAFO, neurophysiological ankle-foot orthosis; PF, plantarflexion; SMO, supramalleolar orthosis.

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NEUROPHYSIOLOGICAL EFFECTSNo conclusive neurophysiological effects were reported

when walking with the AFOs.26,29,30 Spasticity assessed bystudying the median frequency26 and the ratio of maxi-mum Hoffman reflex amplitude to maximum muscle re-sponse amplitude30 of electromyography (EMG) signals didnot show reductions with the use of such AFOs. However,the mean EMG activity of the gastrocnemius muscle wasreported to be better modulated when walking with theAFOs in one study.29

CARRYOVER EFFECTSA potential carryover effect was reported in two studies.15,19

COMPARISON WITH STANDARD AFOSStudies in which comparisons with other types of AFOs

were performed did not show conclusive evidence that AFOswith tone-influencing designs were superior to others. Onlytwo studies17,20 showed more positive effects on gait param-eters in comparison with standard AFOs, whereas oth-ers21,22,26 did not show any significant difference.

DISCUSSIONThis article concisely reviewed the current state of knowl-

edge on the effect of the AFOs with tone-influencing designs.The literature search demonstrated that the relevant studiesmainly involved patients with cerebral palsy, followed bythose with head injury or stroke. Although spasticity is com-mon among these patient groups, it is not clear which ofthem 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 amountof toe extension; 3) the amount of loading on metatarsalheads; 4) the amount of loading at the heel; 5) the amount ofloading on the Achilles tendon insertion area; and 6) thealignment of an ankle joint. Although more recent stud-ies19,23,25–28 adopted DAFOs whose design characteristicswere proposed by Hylton,16 the efficacy of these design pa-rameters requires further investigation.

The AFOs may have positive effect on gait, posture, andEMG data in patients with spasticity. However, it was notconclusive whether they could actually reduce or inhibitmuscle tone. Currently, there is no definitive method toquantify spasticity or muscle tone.31,32 This is one of theobstacles in evaluating so-called tone-reducing or tone-inhib-iting effects. No significant effect in the median frequencysignal26 or Hoffman reflex amplitude30 of the EMG have beenreported with the use of such AFOs. The findings of thesestudies would question their neurophysiological effect. Inaddition, some studies showed that AFOs with tone-influenc-ing designs did not have any significant effects in comparisonwith standard AFO designs.21,22,26 Some studies have alsosuggested that the AFOs may be recommended for use as anadjunct to appropriate physiotherapy, but they might not beeffective if they are used alone.16,18,25

On the basis of the results of this literature review, weconclude that the efficacy of the AFOs with tone-influencingdesigns (i.e., in reducing or inhibiting muscle tone) has notbeen sufficiently proven because of the very low level ofevidence despite the positive clinical effect reported in previ-ous studies. This is because the study design adopted inprecedence studies was not robust enough. The articles re-viewed showed an equivalent range of level of evidence ofGrade C proposed by Sacket.33 Indeed, it is difficult to makea strong argument for a particular position on whether AFOsare able to influence muscle tone when the evidence levelsare so low. This is in agreement with previous publica-tions.34,35 Thus, it would not be appropriate to use the term

Table 4. Clinical effect of AFOs with tone-influencing designs

Clinical effect References

GaitIncrease in walking

velocityDiamond and Ottenbacher17;

Dieli et al.20; Iwata et al.24;Nash et al.29

Increase in step orstride length

Diamond and Ottenbacher17;Dieli et al.20; Radtka et al.21;Lam et al.26; Nash et al.29

Decrease or increase incadence

Diamond and Ottenbacher17;Dieli et al.20; Radtka et al.21;Iwata et al.24

Reduction in excessiveknee flexion

Embery et al.18

Improvement in footfloor contact/loadingpattern/support

Mueller et al.19; Dieli et al.20

Improvement in anklekinematics

Zachazewski et al.11;Radtka et al.21

Reduction in positivesupport reflex

Zachazewski et al.11;Bronkhorst and Lamb15

Reduction in time spentat double stance phase

Nash et al.29

Balance, posture, functionImprovement in

balance, posture andstanding

Harris and Rieffle14; Hylton16;Näslund et al.25

Improvement in GrossMotor FunctionMeasure

Bjornson et al.27

Neurophysiological effectNo reduction in Hmax:

Mmax ratio or medianfrequency

Lam et al.26; Ibuki et al.30

Better modulation ofEMG activity atgastrocnemius

Nash et al.29

Carryover effectPotential carryover

effectBronhorst and Lamb15;

Mueller et al.19

EMG, electromyography; Hmax:Mmax, the ratio of maximum Hoffmanreflex amplitude to maximum muscle response amplitude.

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tone-reducing or tone-inhibiting for such AFOs until theirefficacy is confirmed with grade A evidence level.33

In summary, the following issues need to be further in-vestigated regarding the use of AFOs with tone-influencingdesigns:

1. The classification of patient groups that may benefitfrom these types of AFOs needs to be more accuratelydefined.

2. The design parameters used in these types of AFOs needto be more quantitatively defined.

3. The statistical and clinically significant effects of thesetypes of AFOs in comparison with standard AFOs needto be demonstrated with randomized controlled trials.

The authors would therefore recommend that future stud-ies should carefully investigate these aspects systematically.

CONCLUSIONMore systematic research with randomized controlled trials

is necessary to determine whether AFOs with tone-influencingdesigns would truly have positive clinical effects. Moreover, it isrequired to reexamine whether such AFOs do in fact havetone-reducing or tone-inhibiting effects while ambulating. Iftheir positive effects are confirmed in future studies, it will beessential to investigate their optimal designs and to demonstratewhich group of patients would benefit the most from the AFOs.

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