The effect of tuning ankle foot orthoses–footwear combination on the gait parameters of children with cerebral palsy

Abstract

Background:

There are a wide variety of ankle foot orthoses used in clinical practice which are characterised by their design, the material used and the stiffness of that material. Changing any of these three components will alter the effect of the ankle foot orthosis on gait.

Objectives:

The purpose of this article is to provide an overview on the available research on ankle foot orthosis–footwear combination tuning on the gait characteristics of children with cerebral palsy through a structured review.

Study Design:

Literature review.

Methods:

A thorough search of previous studies published in English was conducted within all major databases using relevant phrases without any limits for the dates. These searches were then supplemented by tracking all key references from the appropriate articles identified including hand searching of published books where relevant.

Results:

To date, there are 947 papers in the literature pertaining to the study of ankle foot orthosis. Of these, 153 investigated the use of ankle foot orthosis for children with cerebral palsy. All the studies included in this review were of a within-subjects design and the evidence levels were generally low.

Conclusions:

The overall results suggested that ankle foot orthosis–footwear combination tuning has the potential to improve the kinematics and kinetics of gait in children with cerebral palsy. However, the review highlights a lack of well-designed and adequately powered studies.

Clinical relevance

While the research described in this article indicates an improvement in the gait of children with cerebral palsy following tuning of their ankle foot orthosis–footwear combination, there is still a paucity of research with quantitative data on the effects of kinematics and kinetics of ankle foot orthosis–footwear combination tuning, comparing untuned ankle foot orthosis–footwear combinations with tuned ankle foot orthosis–footwear combination. Furthermore, current research does not identify the effect of tuning on energy efficiency.

Keywords

Ankle foot orthosis–footwear combination tuning ankle foot orthoses cerebral palsy gait

Background

Cerebral palsy

Cerebral palsy (CP) has often been considered the prototype childhood ‘neurodisability’¹ and has been identified as the most common physically disabling condition.² Overall, global rates of CP are between 2 and 3 per 1000 live births³ and longitudinal epidemiological studies from several countries have reported increased prevalence over time.^4–7

The definition of CP has changed considerably over time due to the complexity of the term. While providing a historical perspective of CP is beyond the scope of this article and is provided elsewhere,⁸ the most recent definition of CP was suggested by Rosenbaum,¹ which reads:

Cerebral palsy describes a group of permanent disorders of the development of movement and posture, causing activity limitation that is attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorders of cerebral palsy are often accompanied by disturbances of sensation, perception, cognition, communication, and behavior, by epilepsy, and by secondary musculoskeletal problems.

Classification of CP

Classification of such a heterogeneous condition is fundamental in research and clinical practice for communicating clearly the type and severity of the condition. The first known classification of CP was by Little,⁹ since then various classifications and approaches to classifications have been used.^10–16 In addition to surgical and therapeutic interventions, orthoses play an important role in the management of the child with CP.

Principles and characteristics of ankle foot orthoses

An orthosis is defined by the International Standards Organisation as ‘an externally applied device used to modify the structural and functional characteristics of the neuromuscular and skeletal system’.¹⁷ Ankle foot orthoses (AFOs) are orthoses that encompass the ankle joint and the whole or part of the foot.¹⁸ AFOs are intended to control motion, correct deformity and/or compensate for weakness.¹⁹

There are a wide variety of AFOs used in clinical practice, which are characterised by their design, the material used and the stiffness of that material. Changing any of these three components will alter the control the AFO has on the patient’s gait.²⁰ There are numerous designs of AFO’s, which due to their make-up differ in how they aim to control the gait characteristics.

Normal and pathological gait

Previous studies have documented typical kinematic and kinetic features present during normal gait.^21–24 They concur that alignment of the ground reaction force (GRF) relative to the joints throughout normal gait is key to producing a controlled, energy efficient gait. However, in pathological gait the demand on the neuromuscular system is greater and control of the GRF is not always possible. AFOs are prescribed in a wide range of gait pathologies in an attempt to influence the kinetics and kinematics of gait and to manipulate the GRF bringing it closer to the joint and thus reducing energy expenditure. Gait pathologies in children with CP have been well documented in previous publications.^25–39

It is clear from the available literature that different designs of AFOs can significantly affect the kinetics and kinematics of gait in children with CP. Research has demonstrated effects on velocity, cadence, stride length, step length, double support, single support, ankle plantar flexion, ankle dorsiflexion, ankle power, knee flexion, knee extension and energy efficiency.^40–70 However, the results reported within this research are variable.

While these studies indicate improvements in certain gait parameters, they are not all in agreement as to which gait parameters are improved with the use of an AFO. One of the reasons for such variation in the research on AFOs may be due to the difference in study design. Some studies compare AFOs to shod and unshod gait, while others compare different designs of AFOs against each other. Furthermore, research on CP children is difficult because CP is not a homogenous disorder and thus comparing the gait of children with differing degrees of disability will inevitably produce variable results. Another reason why there may be variation in the research on AFOs may be due to the lack of ankle foot orthoses–footwear combination (AFO-FC) tuning.

AFO-FC tuning

The importance of tuning AFOs was recognised as early as the mid 1970s when Cook and Cozzen⁷¹ recognised the importance of heel height on footwear in affecting the biomechanics of AFOs in normal subjects.

AFO-FC tuning can be defined as the process whereby fine adjustments are made to the design of the AFO-FC in order to optimise its performance during a particular activity.⁷² The term biomechanical optimisation is used to encompass the whole process of designing, aligning and tuning the AFO-FC.⁷²

The aim of AFO-FC tuning is to optimise the alignment of the lower limbs. During gait, entry into stance and exit from midstance may be optimised by adapting the footwear with rockers and flares to manipulate the GRF.^73,74 Other adaptations include the use of wedges to incline the shank, and changes in the stiffness of the footplate to control knee flexion and extension.⁷⁴

It is imperative to ensure that the angle of the ankle in the AFO (AAAFO) is correct and fully accommodates the length of gastrocnemius. The AAAFO can be described as the angle of the foot relative to the shank in the sagittal plane in the AFO. It is measured as the angle between the line of the lateral border of the foot (base of fifth metatarsal head to the base of the heel) and the line of the shank. It is described in degrees of dorsiflexion, plantar flexion, with plantigrade describing a neutral position.⁷⁵ Furthermore, the design and stiffness of the AFO must be appropriate to control the foot and ankle in all three planes as the gait pathology necessitates.^76–79

The shank to vertical angle (SVA) can be described as the angle of the shank relative to the vertical, measured in the sagittal plane. The SVA is described as inclined if the shank is inclined forward from the vertical and reclined if it is reclined backward from the vertical. It is described in degrees, with vertical being 0°. The line at the front of the tibia is used to represent the line of the shank.⁷⁵

Without AFO-FC tuning the AFO-FC is commonly set at 90°. Common beliefs are that the AAAFO must always be 90° or that dorsiflexion and plantigrade positions are acceptable, but not plantar flexion. This misconception of the ankle/foot complex having to be in a 90° position may have come from the belief that the shank must be vertical to obtain straight knees during gait.⁸⁰ Owen’s⁷⁵ paper indicates that anthropometric measures dictate that an SVA of 10° inclined from the vertical brings the knee joint centre over the middle of the foot during midstance in normal subjects.

Pratt et al.⁸¹ investigated the SVA and the moment arm at the knee joint on 11 healthy subjects in an attempt to establish a baseline for AFO-FC tuning. The research reported a mean SVA of 11.4° ± 3.4° in the barefoot condition and 10.5° ± 3.6° in the shod condition, thus providing support for Owen’s⁷⁵ indication of the position of the SVA during midstance.

Further research has also demonstrated that the shank is not vertical at midstance and there is no place in the gait cycle when both the shank and the thigh are vertical.^{22,23,27,82–84} Owen⁷⁵ suggests that an SVA between 10° and 12° inclined is the optimum position of the shank and allows the thigh to become inclined and thus the pelvis and the trunk to move forward in a vertical position.

From these studies we can deduce that during midstance an element of tibial inclination is required during normal gait. Thus, having an ankle complex and SVA fixed at 90° (when heel/ground contact is maintained) cannot achieve an optimal gait pattern as it prevents the shank from the necessary inclination required. Therefore, it must be recognised that the AAAFO and the SVA are independent of each other and require individual assessments of the patient. Various authors have used different terms to describe the angle between the shank of the tibia and the floor. Owen⁷⁵ used shank angle to floor (SAF), Pratt et al.⁸¹ used shank and the vertical angle (SAV) and Hullin et al.⁸⁵ used the term foot–shank angle, all of which are synonymous with SVA.

Objectives

The aim of this structured review is to detail and discuss the available literature on AFO-FC tuning to see if the process of AFO-FC tuning has further impact on the kinetics and kinematics of gait in children with CP, who already use AFOs to improve their gait. The scope of this review is to look at the biomechanical effects and will work within the boundaries of general mechanical gait characteristics and will not focus on physiological measures.

Method

A thorough review of previous studies was conducted using the following phrases: ankle foot orthosis, AFO, AFO-FC, CP, orthosis, orthoses, orthotics, tuning, splint and gait with no limitations on the date up to spring 2011. The databases searched included PubMed, Cochrane library, PEDro, OTSeeker, Lilacs, Sielo, EMBASE (ovid), Science Direct, psychINFO, Medline (ovid), APAIS Health (informit) PubMed, Recal and Google Scholar. Hand searching of reference lists of review and publications was also undertaken.

Selection criteria

Selection criteria were developed by the primary author based on the nature of the review as dictated by the research questions. To be included in the review, the research had to meet the following criteria:

The intervention involved an AFO.

The subjects were under 18 years and had a diagnosis of CP.

The article demonstrated the effects of AFO on gait.

The study involved a tuning process in that it recognised either or both the SVA and the AAAFO.

The study was published in English as a full paper or a pilot study in a peer-reviewed journal.

Results

To date, there are 947 papers in the literature pertaining to the study of AFOs. Of these, 153 study the use of AFOs in the gait of children with CP. All the studies included in this review were of a within-subjects design and the evidence levels were generally low at 4–5 (based on the Oxford evidence-based medicine (EBM) levels of evidence⁸⁶) as the research available tended to be of a retrospective within-subjects comparison study with no randomised controlled trials carried out.

Twenty-seven papers implemented some form of AFO-FC tuning within the study, and 9 were rejected because they did not include research on both AFOs and children with CP.^87–95 Research by Meadows⁹⁶ was rejected because it was not published in a peer-reviewed journal. Research by Wesdock and Edge⁵⁹ was rejected because the research studied standing ability and not gait. Only 15 papers recognised the importance of either or all AAAFO, SVA and AFO-FC tuning in the gait of children with CP^73,97–110 (see Table 1).

Table 1.

Studies recognising AFO-FC tuning.

Reference	Number and age range of subjects	CP classification	Type of AFO/footwear	Average SAF	AAAFO recognised	Research design	Evidence level	Key findings
Jebsen et al.⁹⁸	N/A	Mixed	Solid AFO	Theoretical 10° inclined	No	Descriptive theoretical paper	5	Recognised that the importance of the SAF inclination of the shank was theoretical. No description of the AAAFO.
Rosenthal et al.⁹⁹	N = 12	Spastic mixed	Solid AFO/regular oxford shoe	Not described but deducible from the data	5° Dorsiflexion	Prospective within-subjects comparison design	4	Used a solid AFO set in dorsiflexion in an attempt to control genu recurvatum. Followed subjects up after 26 months and reported that genu recurvatum was well controlled and gait was improved.
Simon et al.¹⁰⁰	N = 15	Spastic	Solid AFO/regular oxford shoe	10°–15° inclined	7°–10° Dorsiflexion	Retrospective within-subjects comparison design	5	Ambiguity in the description of AAAFO and SAF. Kinematic tuning was by the use of a variable-inclined walk way. Studied genu recurvatum, reported that the tuned AFO produced more normal moments about all joints, especially the knee and in three cases genu recurvatum was controlled fully.
Gans et al.¹⁰¹	N/A	Spastic and athetoid	Soft pliable wrap around AFO	Not given	Plantar grade	Descriptive theoretical paper	5	Recognised that the limitation of adjustability of dorsiflexion can be compensated by heel or sole shoe lifts.
Harrington et al.¹⁰²	N = 11, age = 3.9–16.2 years	Spastic hemiplegic and diplegic	Anterior floor reaction AFO	Not given	5° Dorsiflexion, 5° plantar flexion, 10° plantar flexion	Prospective between subjects comparison design	5	Recognised the importance of the AAAFO described as the angulation angle. Recognised the importance of the stiffness of the AFO. Demonstrated how knee flexion can be controlled by manipulating the GRF.
Nuzzo¹⁰³	N = 10, age = 7–12 years	Mixed	Solid AFO	7°–10°	Recommends dorsiflexion, plantar grade, plantar flexion according to clinical findings	Prospective within-subjects comparison study	4	AFO-FC tuning successfully treated knee hyperextension in seven of the subjects, unsuccessful for three athetoid subjects. Researcher uses posterior flare on footwear.
Sankey et al.¹⁰⁴	N = 29	Hemiplegic spastic	Ambiguous	Not described	Dorsiflexion and plantar flexion	Retrospective between subjects comparison study	5	The research involved issuing 16 of the subjects with dorsiflexed AFOs and 13 with plantarflexed AFOs. They reported that 9 of the 13 subjects issued with a plantarflexed AFO later required surgery, while only 1 of the 16 subjects issued with a dorsiflexed AFO required surgery.
Butler and Nene¹⁰⁵	N/A	Spastic hemiplegia	Solid AFO	Not described	Plantar grade recommended	Descriptive theoretical paper	5	Recognised the effect of using wedges on footwear to manipulate the GRF. Recognised midstance as a vital phase in the gait cycle for AFO-FC tuning. Recognised the effects of tuning on proximal joints. Reported that a heel raise as small as 3 mm can be significant in modifying gait parameters, representing an angular change of 2° floor/shank angle.
Butler et al.¹⁰⁶	N = 5	Spastic diplegia and hemiplegia	Solid AFO	Not described	Not described	Prospective cohort study	3	Subjects presented with knee hyperextension. Gait analysis was conducted before, and 4-to-6 months after, the start of the treatment. The high knee-extending moment arm decreased to a significant level (p < 0.01). In total, three out of five children retained the improvement in barefoot and were weaned from the AFOs.
Owen⁷³	N = 74, CP n = 50, age not given	Mixed	Solid AFO	11.86° Tibial inclination	Dorsiflexion, plantar flexion and plantar grade determined by subjects’ clinical presentation	Retrospective within-subjects comparison study	4	Knee and hip kinetics were optimised with tibia inclined regardless of AAAFO. Full process of AFO-FC tuning described. Recognised midstance as a vital phase in the gait cycle for AFO-FC tuning.
Stallard and Woollam¹⁰⁷	N = 62, age = 1 year 10 months to 15 years 2 months	Not described	Solid AFO	Not described	Not described	Retrospective within-subjects comparison study	4	Improvement in GRF alignment via tuning in more than 68% of subjects. Suggested that tuning should be a routine clinical practice. Suggested that the design of the AFO must have appropriate mechanical properties to successfully manipulate the GRF.
Owen¹⁰⁹	N = 12, age not given	Mixed	Solid AFO	11.86° Tibial inclination	Dorsiflexion, plantar flexion and plantar grade determined by subjects’ clinical presentation	Retrospective within-subjects comparison study	4	Used point-loading rockers to resist early exit from stance phase in crouch gait. Recognised midstance as a vital phase on the gait cycle for AFO-FC tuning.
Butler et al.¹⁰⁸	N = 21, age = 4 years to 12 years 11 months	Mixed	Solid AFO	Not described	Not described	Retrospective within-subjects comparison study	4	Concluded that AFO-FC tuning can improve kinematics and kinetics of gait. Suggests popliteal angle in excess of 45° and hip flexion contracture greater than 15° poor prognostic sign Also suggests that Ataxic gait seems to resist tuning.
Van Gestel et al.¹¹⁰	N = 36, age = 4–14 years	Hemiplegia	PLS dual carbon spring AFO. Orteam AFO	0°–10° inclined	Not described	Retrospective cohort study	4	Concluded that AFOs are optimally aligned when the tibia is inclined between 0° and 10°.
Jagadamma et al.⁹⁷	N = 5, age = 5–12 years	Mixed	Solid AFO	Mean 10.8°	AAAFO was not mentioned in the study	Prospective within-subjects comparison study	4	Compared knee flexion and extension, velocity, cadence and stride length in tuned versus untuned AFO-FC. In children, who presented with knee hyperextension during stance phase, knee flexion increased when AFO-FC was tuned to 3.7° flexion from 2.6° hyperextension (mean maximum knee extension) compared with untuned AFO-FC.

AFO: ankle foot orthosis; AFO-FC: ankle foot orthoses-footwear combination; SAF: shank angle to floor; AAAFO: angle of the ankle in the AFO; CP: cerebral palsy; GRF: ground reaction force; PLS: posterior leaf spring.

Furthermore, only Owen^73,109 recognised the full process of AFO-FC tuning and provided a full description of the process, although limitations in this research were evident.

Discussion

The review of the literature pertaining to AFO-FC tuning revealed a paucity of quality research, which demonstrates the effects of AFO-FC tuning on the kinematics and kinetics of gait compared with untuned AFO-FC. However, the research reviewed did highlight the benefits and the potential of AFO-FC tuning.

All papers included in the review recognise a clear differentiation between the AAAFO and the SVA. However, none of the papers fully explained the reasoning behind the chosen AAAFO for each subject. Owen⁷³ states that the AAAFO for each participant was recorded but did not offer an explanation of how the AAAFO was determined. Several of the early papers were clearly just beginning to recognise the importance of the AAAFO and experimented by setting different AAAFOs on subjects and observed the effects during gait. The AAAFO in these papers clearly did not reflect the length of gastrocnemius as is intended in AFO-FC tuning.

The SVA was often identified in the research, but was not always described. Gans et al.,¹⁰¹ Sankey et al.¹⁰⁴ and Butler and Nene¹⁰⁵ identify the SVA, but they do not describe the SVA used in degrees and this cannot be deduced from the data.

The SVA identified by Jebson et al.⁹⁸ and Nuzzo¹⁰³ comes from a theoretical kinematic justification as tuning was either carried out on one patient or none at all. Butler et al.^105,106,108 and Stallard and Woollam¹⁰⁷ recognise the importance of tuning and describe the benefits on gait, but do not provide the angle of the SVA.

Rosenthal et al.,⁹⁹ Simon et al.¹⁰⁰ and Harrington et al.¹⁰² do not report the tuned SVA’s of AFO-FC on children with CP, although the SVA’s can be deduced from the data. Owen,^73,109 Van Gestel et al.¹¹⁰ and Jagadamma et al.⁹⁷ all describe the SVA used in their research.

The SVA’s reported or deduced from the data range from 0° to 15° inclination. However, it is difficult to compare the individual figures because the process of AFO-FC tuning is variable in the literature with some papers not tuning the AFO-FC at all, but still recognising the importance of the SVA and its effects on gait. Furthermore, the terminology used is ambiguous until it was clearly described and standardised by Owen.⁷⁵

Early studies which began to recognise the importance of the affect of one or all of the AAAFO, SVA and the footwear on gait did not offer great detail on the process involved with AFO-FC tuning, instead the research tends to be of a descriptive theoretical nature describing how the GRF can be manipulated by altering the angle of the ankle and the inclination of the tibia.

Nuzzo¹⁰³ studied 10 cases of athetoid and ataxic CP children, all of whom presented with genu recurvatum at heel strike/initial contact. Each subject wore a solid AFO, which was set in dorsiflexion. Tibial inclination was set between 7° and 10°. A posterior heel flare was added to the shoe of each subject in an attempt to manipulate the GRF, thus causing a knee flexion moment. The results showed a decrease in knee hyperextension at initial contact, which was deemed successful for seven of the subjects and unsuccessful for the three athetoid cases. The study demonstrated the potential to affect the kinetics and kinematics of gait by considering the AAAFO and the SVA; the footwear in this study was also modified to affect entry into gait at the first rocker. Unfortunately, Nuzzo¹⁰³ does not describe the physical presentation of the subjects studied. There is also a lack of detail on the description of the AFO used, in terms of design and stiffness. The research identifies the successful manipulation of the GRF and how gait can be affected by changing the AAAFO and SVA, but it does not describe optimal AFO-FC tuning for the individual subject/clinical presentation.

However, Butler and Nene¹⁰⁵ identified how even very small changes to the AFO-FC could result in significant effects on the GRF. This research reported that a heel raise as small as 3 mm can be significant in modifying gait parameters, representing an angular change of 2° of the floor/shank angle. Furthermore, this was the first study to use a video image of the patient overlaid with a thin white line representing the position and magnitude of the GRF to aid in clinical decision making. Unfortunately, the paper was descriptive and was based on theoretical principles rather than empirical data.

Butler et al.¹⁰⁶ investigated the effect of tuned AFOs in conjunction with balance training exercises. The study investigated five children with CP who presented with hyperextension of the knee joint during midstance. Gait analysis was conducted before, and 4-to-6 months after, the start of the treatment. The high knee-extending moment arm decreased to a significant level (p < 0.01) and was closer to normal. Three out of five children retained the improvement in barefoot, and were weaned from the AFOs. Butler et al.¹⁰⁶ attributed this effect to motor learning, which might have been facilitated through the use of tuned AFO-FCs. However, the study presented some limitations. The participants underwent a number of treatments and thus the results cannot be attributed to AFO-FC tuning alone. The study did not provide details on the methods used for tuning and lacked comparison between tuned and untuned AFO-FCs. The authors also failed to provide sufficient details on the materials and design of AFOs and the prescription process of AFOs to each subject with regard to their clinical presentation.

Later research by Owen⁷³ studied independently ambulant children with neurological conditions, including CP, using solid AFOs via a transportable video vector generator (VVG). The tuning process is described as making fine adjustments to the tibial inclination angle of each AFO using a series of wedges under the subjects’ heel, in an attempt to manipulate the position of the GRF. The research reported that in all the subjects tested, optimal knee and hip kinetics were all achieved with the tibia inclined regardless of the AAAFO. While the mean SVA for all the AFO-FCs (n = 112) after tuning was 11.36° ± 2.08° (range = 7–15), the mean for AFO-FCs used by children with CP (number of legs = 69) after tuning was 11.86° ± 2.05°. The author went on to suggest that 10°–12° SVA was a good starting point from which to begin tuning AFO-FC.

The study indicates that AFO-FC tuning has a positive effect on gait by adjusting the location of GRF, thus affecting its relationship to the lower limb joints. While the study describes the process of tuning AFO-FC, describing how to manipulate the GRF, it does not provide quantitative kinetics and kinematics of the gait of children with tuned and untuned AFOs. The research measures the SVA at midstance while the patient is static; however, there is no research to suggest that the SVA measured statically will represent the SVA at midstance during gait.

Further research by Owen,¹⁰⁹ involved a retrospective comparison study on 12 CP children using solid AFOs with point-loading rocker modifications, in an attempt to align the GRF for terminal stance (TST) by adjusting the design of the footwear. Owen¹⁰⁹ reports that GRF alignment, anterior to the knee and posterior to the hip in TST of normal barefoot gait, is achieved by the combination of maintenance of a relatively fixed ankle in appropriate dorsiflexion and use of metatarsal phalangeal joint (MTPJ) extension, third rocker, in order to produce appropriate inclination of the shank relative to the vertical. The study suggests that an AFO can achieve this, but inappropriate accompanying footwear may reduce the chances of success.

This research reported that the rocker modifications resisted early exit from stance in crouch gait. The study concluded that point-loading rockers were most successful with the apex in front of the MTPJs at 78% of the length of the footwear. Although an AFO can retard tibial progression, it may prove inadequate if the anatomical third rocker allows the knee centre to pass in front of the GRF too early in TST. Thus, the theory behind the anteriorly placed point-loading rocker is to resist tibial progression further by manipulating the GRF away from the joint centre, thus producing a high-moment arm anterior to the knee and encouraging knee extension.

Unfortunately, the physical presentation of the subjects studied in Owen’s^73,109 research was not reported and no detail was given on how the prescription of the AFO was devised and thus if gastrocnemius was fully accommodated, although the author states such data were collected, it is not reported. The design of the AFO in terms of its material and stiffness and the footwear combination is recognised as playing an integral part in the ability to produce an optimal gait pattern when prescribing AFOs; however, the research lacks detail on the material and stiffness used for the AFO and a detailed design of the AFO.

A later study by Stallard and Woollam¹⁰⁷ aimed to establish the potential of the VVG to achieve, in a community setting, more effective orthotic outcomes for patients in whom alignment of GRF is an important treatment objective. In total, 61 children were studied, all of whom had their gait assessed and then optimally tuned in line with the principles of AFO-FC tuning by Butler and Nene.¹⁰⁵ This research reported that improved biomechanical alignment of the lower limbs was achieved in 68% of the subjects; only 2 of the 61 subjects failed to show a significant improvement. The study also noted that the AFO design must have appropriate mechanical properties. From this study, it was concluded that tuning with kinematic and kinetic monitoring should become routine clinical practice.

Stallard and Woollam¹⁰⁷ did not produce any quantitative kinetic or kinematic data; instead reporting in a qualitative manner, they did not provide descriptions of the joints that were being investigated. Successful tuning was decided by assessment features, for example, ‘improvement of alignment of the GRF by a minimum of 10 mm to the ideal specified by the physiotherapist’. This study also failed to describe the neurological disorders which the participants presented with or the extent of the gait pathology. Unfortunately, the only description of the AFOs used was a solid AFO made from polypropylene. There is no mention of the type or thickness of polypropylene, the physical presentation of the patients and the justification of the orthotic prescription, although the study did note that this was all confirmed and agreed prior to tuning.

Further research by Butler et al.¹⁰⁸ tried to establish the characteristics of children with CP which could be identified as predictors of successful tuning. Data from 21 children were retrospectively analysed. Parameters were identified by statistically comparing the data from children who were successfully tuned with data from children who were not. The study concluded that analysis of knee kinematics prior to AFO use would be a good predictor of potential success. This research indicated that the most successful predictors were maximum knee flexion no more than 20° in the initial one-third of stance phase, and movement towards knee extension in the second-third of stance to 10° flexion or less. Poor prognostic signs were considered to be knee flexion greater than 35° in the first-third of stance and greater than 15° in midstance and a popliteal angle in excess of 45° and a hip flexion contracture greater than 15°. Although the study suggested that ataxic gait was not successfully tuned, it referred to only one subject with ataxic gait. One of the issues with this study is that the authors considered kinematics and kinetics of the knee and failed to recognise the effects on the proximal joints. Furthermore, the comparison of data was between barefoot and tuned AFO-FCs rather than tuned and untuned AFO-FCs; therefore, it is unclear how much of the improvement was due to AFO intervention and how much was due to AFO-FC tuning.

Furthermore, the only reference to the AFO used in Butler et al.’s¹⁰⁸ study was ‘a fixed AFO’ and no further description was given. This clearly lacks the detail required to ensure optimum AFO prescription and assessment had been realised. A description of footwear used was also omitted. However, unlike previous studies, Butler et al.¹⁰⁸ did provide data on the physical examination of each participant and there was no explanation of how the physical presentation of each participant was related to the AFO prescribed. Although the aim of this article was to determine a screening tool for AFO-FC tuning, the investigation used subjects who had received AFO-FC prescription and tuning; therefore, the details of this process are required to ensure accuracy.

Van Gestel et al.¹¹⁰ studied 36 children with hemiplegic CP. The study compared three different types of AFOs, and each permitted dorsiflexion. The study reports that the AFOs fitted to these children were optimally tuned. The description used for optimal tuning was having the shank in alignment ranging from neutral to a maximum of 10° inclined. Unfortunately, the process of determining how the AFOs were considered to be optimally tuned was not described. It is difficult to see how a dorsiflexion permitting AFO could be optimally tuned throughout stance phase. Furthermore, the study describes the subjects as a ‘homogenous’ group. It is difficult to see how this term could be applied to a group of children with a diagnosis of CP.

The only description of the clinical presentation of the subjects was that they all presented with a plantar flexion–knee extension couple. The AFOs are described as being individually selected and adapted but no detail is offered to justify the prescription, although a detailed description of the design of the AFOs is given. The research states that the gait analysis determined the amount of flexibility in the orthosis. The study also reports that bilateral AFOs were issued for hemiplegic subjects to promote symmetry, but does not offer any research to justify this theory. The study also fails to recognise the importance of the AAAFO in AFO-FC tuning and possibly the length of gastrocnemius.

The only paper to provide quantitative kinematic and kinetic data for tuned and untuned AFO-FC was that of Jagadamma et al.⁹⁷ This pilot study involved a small group of five CP children who all presented with knee hyperextension during stance phase. Gait analysis was carried out before and after tuning the child’s current AFO-FC prescription. The results show that mean maximum knee hyperextension decreased from 2.6° extension to 3.7° flexion. However, velocity, cadence and stride length all decreased in the tuned AFO-FC, although not significantly. This may have been due to a lack of familiarisation in the tuned AFO-FC as the participants were not given any time to acclimatise to the new AFO-FC. The study lacked power and statistical significance, which is most likely to be due to the small sample size. Unfortunately, Jagadamma et al.’s⁹⁷ study does not describe the physical characteristics of the participants, and there is no information regarding the AAAFO or how the prescription for the AFOs was justified. The study fails to provide details on the design and material of the AFOs used and their justification. The study also only looked at the knee joint and therefore proximal joints were not considered.

While the research described in this article indicates an improvement in the gait of children with CP following tuning of their AFO-FCs, there is still a paucity of research with quantitative data on the effects of kinematics and kinetics of AFO-FC tuning, comparing untuned AFO-FCs with tuned AFO-FCs. Current research does not identify the benefits of AFO-FC tuning to the patient, while improvements in kinematics are usually studied in isolation, for example, improvement of knee hyperextension at initial contact, without studying the effects on the proximal joints. Thus, whether the reported improvement in some gait parameters results in a more efficient gait for the patient still requires investigation. Current research does not identify how energy consumption is affected in tuned AFO-FCs. If energy efficiency is improved with a tuned AFO-FC, it must be significant enough to warrant the extra time and financial implications required to carry out the tuning process.

From current research, it is unclear whether tuned AFO-FCs can maintain/increase muscle length and hence prevent/reduce deformity developing over time. Further research is required to investigate the effect on the triceps surae in an optimally tuned AFO-FC when the foot is in a plantarflexed position; if the muscle increases its passive range of motion (ROM) over a period of time while the subject ambulates in a tuned AFO-FC, this may indicate that the posterior musculature is achieving a significant stretch, a key aim of treatment when prescribing AFOs to children with CP. Longitudinal studies may be required to measure the true effects AFO-FC tuning has on the triceps surae.

Further research is also required to determine whether the cosmesis of a tuned AFO-FC (which can require large rocker soles) affects patient compliance.

In 2008, the International Society of Prosthetists and Orthotists (ISPO) recognised the importance of AFO-FC tuning.¹¹¹ In 2009, National Health Service for Scotland (NHS Scotland) reported that the provision of a solid AFO without tuning can introduce further neurobiomechanical challenges to patients and recommended that AFO-FC tuning should be standard clinical practice when issuing an AFO.¹¹² It is recognised that a suboptimal AFO-FC may have an immediate detrimental effect on function and in the longer term it may actually contribute to deterioration.¹¹³ Despite this, AFO-FC tuning is still not routine clinical practice.

However, there are barriers to tuning AFO-FCs as standard practice; the algorithm produced by Owen⁷⁴ may be deemed as complicated. Current literature recommends the use of two-dimensional/three-dimensional (2D/3D) gait analysis,¹¹³ which is expensive and not easily accessible to the majority of clinicians. However, there is no available research to demonstrate whether 2D/3D gait analysis is essential to tune AFO-FCs.

The design of the AFO and the correct prescription for the patient in terms of material stiffness, type and trim lines are critical and is yet to be standardised. The lack of a definitive clear process of how such an assessment and AFO prescription should be devised has led to studies lacking crucial details, which result in a failure to inform future research and preventing generalisation and replication in the clinical setting.

Recommendations

In light of this review, the authors recommend that future research on AFO-FC tuning should include the following details, several of which were also recommended by Bowers and Ross¹¹⁴:

Complete and detailed description of the subjects, including age, diagnosis and detailed classification of CP and presenting gait pathology. The use of any walking aids.

Complete and detailed physical assessment of the subjects’ lower limbs, including ROM of all lower limb joints passive and dynamic, highlighting whether range is attained with ease or difficulty. Particular reference should be paid to dorsiflexion range with knee extended, which is an indication of gastrocnemius length and is critical in the prescription of AFOs. Any fixed deformities should be reported, together with an assessment of muscle spasticity, including tone, contractures, torsional abnormalities affecting the foot progression angle and alignment of the subtalar joint.

Current and previous treatment of each subject, including surgery, therapy and in particular botulinum toxin.

Details of the AFO and footwear should be described and include the following: material and thickness used, flexibility and stiffness properties in stance, trim lines, fastenings, stiffeners, hinges, ROM, AAAFO and SVA and the process used to achieve these. The design of footwear, heel type height and pitch addition of rockers and stiffeners and materials used. Critically, there should be a reasoned clinical justification for the individual prescription of the AFO-FC, with details of how the length of gastrocnemius has been accommodated.

Studies should give sufficient details on the effects of AFO-FC tuning versus untuned AFO-FCs with the provision of quantitative kinematic and kinetic data. Researchers should be clear on whether tests have been conducted on the same or different days, whether there has been a period of acclimatisation, order of testing and whether subjects have been tested with or without footwear and whether the control group has been tested with or without footwear.

Conclusion

There is emerging evidence that tuning AFO-FCs can significantly improve their effectiveness. However, the paucity of research into AFO-FC tuning, the lack of access to 2D/3D gait analysis for the majority of clinicians, the time and cost required to tune AFO-FCs and the lack of research into the benefits to the patient are major contributing factors as to why AFO-FC tuning is not currently standard practice. Furthermore, the poor design of research studies on AFO-FC tuning and the lack of details provided in such studies prevent a clear conclusion on the effects of AFO-FC tuning on gait, prevents replication of studies and most importantly prevents research being converted into clinical practice.

Footnotes

Funding

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

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