Research Toward Understanding the Benefits and Limitations of Orthotic Use To Improve Mobility and Balance for Individuals With Neuropathic Conditions

Abstract

Background:

Walking is a vital activity often compromised in individuals with neuropathic conditions. Charcot-Marie-Tooth (CMT) disease and Cerebral Palsy (CP) are two common neurodevelopmental disabilities affecting gait, predisposing to the risk of falls. With guiding scientific evidence limited, there is a critical need to better understand how surgical correction affects mobility, balance confidence, and gait compared to ankle foot orthosis (AFO) bracing. A systematic approach will enable rigorous collaborative research to advance clinical care.

Methods:

Key elements of this vision include 1) prospective studies in select patient cohorts to systematically compare conservative vs. surgical management, 2) objective laboratory-based evaluation of patient mobility, balance, and gait using reliable methods, and 3) use of patient-centric outcome measures related to health and mobility.

Results:

Valid and reliable standardized tests of physical mobility and balance confidence have been described in the literature. They include 1) the four-square step test, a widely used test of balance and agility that predicts fall risk, 2) the self-selected walking velocity, a measure of general mobility able to detect function change with orthosis use, and 3) the activity specific balance confidence scale, a survey instrument that assesses an individual’s level of balance confidence during activity. Additionally, motion capture and ground reaction force data can be used to evaluate whole-body motion and loading, with discriminative biomechanical measures including toe clearance during the swing phase of gait, plantarflexion at 50% of swing, peak ankle plantarflexor moment, and peak ankle push-off power.

Conclusion:

The tools needed to support evidence-based practice and inform clinical decision making in these challenging patient populations are all available. Research must now be conducted to better understand the potential benefits and limitations of AFO use in the context of mobility and balance during gait for individuals with neuropathic conditions, particularly relative to those offered by surgical correction.

Clinical Relevance:

Following this path of research will provide comparative baseline data on mobility, balance confidence, and gait that can be used to inform an objective criterion-based approach to AFO prescription and the impact of surgical intervention.

Introduction

Walking is an important functional activity that is often compromised in individuals with neuropathic conditions. Charcot-Marie-Tooth (CMT) disease and cerebral palsy (CP) are two of the most common neurodevelopmental disabilities, affecting >1 million children in North America. CMT and CP are leading causes of lifelong physical disability in children,¹ often causing altered gait biomechanics (i.e. joint motion and loading) due to disruption of the central and peripheral nervous systems, which can occur any time during fetal development through early childhood.^1,2 Impaired walking or altered gait presents several additional risk factors for individuals with CMT or CP: increased falls risk and increased prevalence of osteoarthritis (OA).

Individuals with neuromuscular diseases are particularly at risk of falls due to locomotor impairment. Amongst patients with CMT, impaired walking is the most significant contributor to reduced quality of life.³ A recent cross-sectional survey of 252 patients with CMT found that 86% of survey respondents reported falls or near falls.⁴ The impact of falls is far reaching, in terms of injury risk and the consequences of the fear of falling. The most cited reasons for falls or near falls included muscular weakness with tripping due to foot drop or joints giving away.⁴

Altered gait and balance deficits lead to potential fall risk

CMT comprises a group of progressive inherited neuropathies that affect motor and sensory axons of the peripheral nervous system. Depending on the axons affected, motor and sensory function is progressively impaired, typically beginning in the longest axons and progressing proximally over time. Affected patients typically have progressive distal weakness, muscle atrophy and sensory loss, first in the feet and lower legs, followed by the hands.^5-7 In mild and moderate cases, individuals with CMT exhibit associated problems including cavovarus foot deformity, footdrop, and sensory changes.^8,9 These impairments result in altered gait and balance deficits.¹⁰

The ankle plantarflexor muscles play a critical role in supporting the body and maintaining balance during the stance phase of gait. During stance, the plantarflexor muscles support the body preventing knee buckling and forward rotation of the tibia, and during push-off the plantarflexor muscles propel the body and limb forward.¹¹ During swing phase, the dorsiflexor muscles lift the foot to allow clearance of the toes to prevent tripping. Ankle weakness in individuals with CMT can alter the ability to maintain balance, support the body, push the limb into swing phase, and lift the foot during swing to clear the toe, predisposing individuals with CMT to greater risk of falling.

Altered gait potentially leads to increased risk of osteoarthritis

Individuals with pediatric-onset of musculoskeletal impairments, such as CP, have a 10 times greater likelihood of musculoskeletal disease.² For example, up to 32% of individuals with CP have OA, which is drastically higher than the general population (14%), with individuals developing this condition in their early-to-mid 20s in contrast to the usual onset during middle-age.² Reported odds ratios for OA were up to 5 times higher for CP patients across all age groups, with younger age groups having higher odds ratios than older age groups compared to age-matched individuals without CP.² It is suspected that altered joint motion (i.e., kinematics) contributes to the development of OA, which involves the degeneration of joint tissues, and can cause pain, discomfort, and functional limitations. Previous studies on OA prevalence in individuals with CP are limited to 1) reported hip, hand, knee, and polyarticular OA;^12,13 2) scant data regarding the influence of CP disease severity; and 3) no reported biomechanics.

Foot deformities, such as equinovalgus, equinovarus, and planovalgus, affect more than 62% of individuals with CP.^12,13 Foot deformities can cause gait abnormalities and increased loading in concentrated areas of the foot, particularly the midfoot, which likely contribute to increased rates of OA.

Treatment considerations

The lack of research on lifespan issues, such as falls and OA risk, and longitudinal studies that bridge childhood to adulthood in individuals with CP has gained attention. Specifically, adults with CP and parents of young children with CP, have requested research on CP be more focused on longitudinal studies across the age span and clinical spectrum, particularly focused on pain, fatigue, exercise, health, and wellness.¹⁴ Not reported was the participant demographics (e.g., sex, ethnicity, background, or socioeconomic status), making it unclear how representative these opinions are of the broader community, especially members of equity-deserving groups. The perspectives of local equity-deserving communities for research endeavors focused on CP, as well as more broadly on musculoskeletal and neurodevelopmental disorders, are needed to respond with allyship and action.

Ankle foot orthoses (AFOs) are commonly used by individuals with CMT or CP, often with the intent of improving mobility, managing pain, reducing the risk of falls, and restoring a more normal gait pattern. Although AFOs are non-invasive and adjustable, they can be bulky, uncomfortable, and destabilizing for already weak individuals. Individuals with CP have high rates of foot deformity,^12,13 which often require surgical intervention. Similarly, while great strides have been made in treating cavovarus deformity in CMT, as evidenced by a recent consensus statement,¹⁵ there remains limited information on gait and outcomes data related to balance after operative fixation. Surgical correction offers the advantages of improving limb alignment and reduced bulk while also avoiding the sometimes-arduous task of donning/doffing a brace. However, surgery carries risk, has potential complications, requires post-operative recovery, and requires re-operation if the initial goals are not achieved.

Scientific evidence needed to aid in clinical decision-making

Weight bearing CT has greatly improved our understanding of bony morphology associated with foot deformities that are not easily appreciated on plain radiographs (Figure 1). AFOs are commonly prescribed to individuals with CMT and CP to support the foot and ankle and restore mobility by compensating for progressive distal limb weakness, fatiguability, foot deformity, and decreased sensation. However, AFO adherence is suspected to be marginal, and there is little evidence that AFOs help with weightbearing problems or improve foot biomechanics.

Figure 1a to 1c.

WBCT volumetric rendering of the foot and ankle of a patient with CMT and cavovarus foot deformity. Morphologic measurements can be made from appropriate WBCT slices (inset images) pre- and post-op to assess the deformity and correction achieved – (1a) cuneiform-to-floor distance, (1b) forefoot arch angle, and (1c) transverse arch plantar angle.

This lack of data stems partly from the use of traditional motion capture techniques that are reliant on skin markers to measure foot segment motion, which prevents measurement of individual bone movement while individuals are shod and wearing their AFO. To counteract these limitations, a recent study employed dual fluoroscopy (DF), which leverages two orthogonally-placed X-ray videos to measure 3D bone movement (e.g., Figure 2), and found alterations in the medial longitudinal arch of individuals with pes planus (i.e., flat feet).^16,17 However, DF studies have not yet investigated individuals with CMT or CP. Quantification of 3D foot biomechanics is critical to evaluate AFO efficacy and the AFO-induced changes that may prevent OA. Evidence of this sort could increase AFO adherence and decrease OA rates among patients with neurodevelopmental disorders and foot deformity.

Figure 2.

3D model-based tracking of calcaneus in dual fluoroscopy images (top). Tibiotalar, subtalar, and talonavicular joint angles during stance phase of gait are shown for one female volunteer (bottom).

A patient must be committed to wearing an AFO for any of its potential benefits to be realized. As alluded to above, many factors can negatively influence a patient’s satisfaction with their braces such as discomfort, device appearance, limited footwear options, and the quality of clinical services provided when receiving an AFO. Additional considerations include the potential for wounds in patients with diminished sensation, and financial costs.

More data are needed to achieve optimal clinical AFO prescription. Despite small studies indicating positive effects, and widespread clinical use due to their expected benefits, there is no universal, literature-based consensus to inform decision-making for whether orthoses are indicated for a particular patient with CMT, and if so, what type of device should be prescribed.^18-21 Improved insight into the benefits and limitations of clinically provided AFOs will facilitate the development of more systematic and evidence-based refinements of AFO prescription, fitting and design.

Scientific evidence to help surgeons determine if an AFO or a surgical procedure are best for a given patient, especially in the setting of a brace-able foot, also remains limited. Recent consensus among expert orthopedic foot and ankle surgeons is “There are no evidence-based orthopedic studies to help determine optimal timing for surgery, and there is often contradictory advice from the patient’s neurologist, physical therapist, and orthotist regarding the role of an operation.”¹⁵ There is a critical need to understand how surgical correction affects mobility, balance confidence, and gait compared to AFO bracing in the native foot (non-operatively treated). Without such information, an evidence-based approach to answering this critical question will likely remain unrealized. In addition, how surgical correction of the cavovarus foot alters gait, specifically regarding restoration of joint position, control, and balance remains unknown. Optimizing interventions to improve balance and reduce falls for individuals with CMT will require a better understanding of alterations in gait biomechanics as they relate to AFO use and surgical correction.

Approximately 20% of patients with CMT present to the orthopedic office with no motor function below the knee and no significant deformity.¹⁵ AFOs present a reasonable first line treatment to improve gait and balance. Neuromuscular patients demonstrate varied AFO stiffness needs for optimal and efficient gait.²² How their individual needs change after surgical correction, and what deficits may persist, is unknown. A recent study on 37 individuals with neuromuscular disease showed that while all AFO stiffness levels evaluated improved walking energy costs (15-19% decrease) and speed (20-24% increase) compared to shoes only, individually optimizing the AFO stiffness improved these parameters further.²² This finding highlights the benefits of AFO use as well as the uncertainty in optimizing care. Understanding the resulting gait after surgical reconstruction in comparison to brace management may allow us to further refine and guide surgical decision making and provide insight into the relative costs and benefits of bracing and surgical management.

The overall objective of the proposed research approach is to characterize the benefits and limitations of AFO use and surgical correction in the context of gait, mobility, and balance in individuals with neuropathic conditions. This has the potential to be profoundly impactful to these patient populations as impaired walking is the most significant contributor to reduced quality of life in patients with neurodevelopmental disorders.³ The comparisons embodied in this research approach represent important steps toward understanding the effects of AFO use and surgical management on balance and mobility. Further, they move us toward a longer-term goal of optimizing bracing strategies, the timing and selection of treatment options (surgical and orthotic), and postoperative management in neuromuscular patients with cavovarus foot deformity. Expected outcomes from such research are that we will have comparative baseline data on mobility, balance confidence, and gait that can then be used to inform an objective criterion-based approach to AFO prescription and the impact of surgical intervention.

Methods

The objective of the proposed research approach is to address a knowledge gap related to mobility, balance confidence, and gait biomechanics in individuals with neurodevelopmental disorders who have, and have not, undergone surgical correction. Patients will be recruited from a variety of populations. Recruitment at dedicated research-centric clinics can draw individuals with peripheral neuropathies from across the USA and internationally. Additional recruitment strategies may be needed to reach individuals who cannot afford healthcare (e.g., indigenous populations) and are believed to be at a much higher risk for CP than the general population.

Study Populations

Studies should include, at a minimum, two groups of individuals with CP and CMT: 1) those who have undergone surgical correction; and 2) those who have not undergone surgical correction but use an AFO. The sample needs to reflect the general characteristics of individuals with neurodevelopmental conditions seeking medical care, enabling research studies that can provide preliminary data on which to base future mechanistic and intervention studies.

Inclusion Criteria: 1) Clinical diagnosis along with genetic confirmation of CMT or CP; 2) age between 12 and 75; 3) able to walk at a slow to moderate pace without an AFO, 3) able to read and write in English to provide written informed consent, provide informed consent through a translator, or surrogate provided consent; 4a) individuals in any AFO group must have an AFO prescribed for daily activities; 4b) individuals in any surgical group will also have had surgical correction of bony deformity focused on muscle balancing and hindfoot correction.

Exclusion Criteria: 1) Other causes or risk factors for peripheral neuropathy (for example diabetes, ETOH abuse); 2) uncorrected visual impairment; 3) history of musculoskeletal injury requiring surgery; 4) loss of plantar protective sensation; 5) pain >4/10 while walking (or an increase in pain during testing of >2/10); 6) for the AFO group, prior surgical correction of a foot deformity focused on muscle balancing and hindfoot correction.

Physical performance measures

Participants must be evaluated using valid and reliable tests of physical mobility, balance confidence, and gait biomechanics. Individuals in any surgical treatment group would complete all activities without an AFO, and individuals in the AFO group would complete activities with and without their clinically prescribed AFO, to determine the effect of AFOs on mobility, balance confidence, and gait biomechanics. These findings must then be compared to falls frequency, assessed by asking participants the number of times they fell in the previous 24 hours and the previous week. Participants would also report their specific circumstances most associated with a fall events. Longitudinal follow-ups would be employed to ascertain how mobility, balance confidence, and gait biomechanics change due to AFO use or following surgical correction and to determine the prevalence and time to OA onset for these individuals.

The primary performance-based mobility measure is the four-square step test (4SST), a standardized and widely used test of balance and agility that predicts fall risk in multiple patient groups.^23-25 The test of functional mobility requires rapid stepping and changes in direction, that are often limited by lower limb pathology. The measure has good to excellent reliability and validity across multiple patient populations and groups, is a key dependent measure in multiple AFO related studies and has demonstrated ability to detect changes in function in individuals with lower limb pathology and AFOs.^23-25

Self-selected walking velocity (SSWV) is a well-accepted measure of general mobility that is useful for studying individuals of a wide range of ages, disease conditions, and injury types.^26-30 Self-selected gait speed has excellent reliability, ability to detect function change with orthosis use, and is an early indicator of reduced participation.^27-32 Participants are instructed to walk at their “normal comfortable” pace for a 10 m distance. The time traveled between the 2 m mark and 8 m mark is recorded in seconds, and two trials are completed with rest between trials.

The activity specific balance confidence scale (ABC) is a well-established survey instrument used to assess a participant’s level of balance confidence during functional activities.³³ The ABC has been used to characterize deficits in confidence associated with CMT. In this patient population it has been associated with patient report of falls and functional mobility tests.³⁴ The ABC scale takes approximately 3 minutes to complete.

Results

The following sections summarize data from experiments previously conducted over the past decade that support elements of this vision for establishing an evidence base for treatment decision-making in individuals with neuropathic conditions.

Patient acceptance of AFOs

Over 300 individuals with CMT who use an AFO were previously queried, utilizing multiple standardized questionnaires including the Orthotics and Prosthetics Users Survey (OPUS).³⁵ We sought to gain insight into the relative satisfaction with daily use AFOs and patient experience with the clinical fitting process. We included also the Activities Specific Balance Confidence Scale (ABC)³³ to evaluate balance confidence in individuals with CMT who use an AFO. The OPUS includes 11 device-specific questions and 10 service-related questions, with patients rating their level of agreement to statements using a six-level Likert scale. Stronger agreement indicates greater satisfaction. Participants were also given an option to elaborate on what they would change about their orthosis, and what activities their orthoses help with and limit.

A total of 314 CMT individuals completed both subscales of the OPUS.³⁶ Over one third of individuals who used AFOs provided negative responses to multiple questions regarding their AFOs. Among the group, 42% indicated they disliked the appearance of their AFO, 32% experienced discomfort, 35% experienced abrasions or irritations, and 36% experienced pain with AFO use (Figure 3). Aligned with these data, participants indicated poor compliance with wearing the AFO, especially if patients felt a sense of constriction, aesthetic problems, difficulty finding normal shoes that fit with bulky AFOs, or if cost was an issue.

Figure 3.

To gain insight into satisfaction with daily use, 329 individuals with CMT who use an AFO were queried utilizing a questionnaire that included 11 device-specific questions and 10 service-related questions. Patients rated their level of agreement to statements using a six-level Likert scale. Less than half of participants strongly or very strongly agreed that their orthosis was pain-free to wear, and only half similarly agreed that their orthosis is comfortable to wear throughout the day. These findings suggest the need to further enhance AFO related care to overcome the weakness, pain, and impaired function associated with CMT. (Expanded from Zuccarino et al. 2021).36

Individuals with CMT indicated overall satisfaction with their AFO but also specific areas for improvement. The ABC data demonstrated impaired balance confidence in individuals with CMT despite the use an AFO. Further, many participants reported falling in the preceding 24 hours (14% of participants) or week (38% of participants). Despite the high rate of falls, 78% of participants indicated their AFOs improved their balance. The efficacy of AFO use in other neurological conditions has been explored with improvements in gait function, independence, confidence and energy cost.^20,37

Gait laboratory evaluations can be done reliably and consistently across sites

Optoelectronic motion capture and ground reaction force data are routinely used to evaluate whole body motion and loading as participants walk at self-selected speed and a controlled speed based on leg length.^38,39 An array of retro-reflective markers, placed on the skin of a participant to minimize skin-bone movement, track the position and orientation of body segments using well established methods.³⁹ Force plates embedded in the floor capture ground reaction forces. Data from a minimum of five successful trials are analyzed using Visual-3D software package (C-motion Inc., Germantown, MD). The ability to collect reliable data within and across sites using these methods has been previously demonstrated.³⁵ Biomechanical dependent measures include toe clearance during the swing phase of gait, plantarflexion angle at 50% of swing, peak ankle plantar flexor moment, and peak ankle push-off power.^40,41 Time series data for ankle, knee, and hip kinematics and kinetics will be determined.

DF provides the ability to image and measure individual bone movement within the foot and ankle. While data from DF in these populations are limited, the methodology shows great promise. Participants will perform walking and sit-to-stand activities with and without their AFO, as applicable, while DF images are acquired. CT scans will be acquired of bilateral tibia through toe-tips of all participants. CT images will be segmented to create 3D models of the tibia, talus, calcaneus, navicular, and cuboid. Bone models will be overlaid on the DF images to track 3D bone movement during each activity (Figure 4). Anatomical coordinate systems are defined for each bone and applied to the DF-tracked data to calculate kinematics for the tibiotalar, subtalar, talonavicular and calcaneocuboid joints. Statistical parametric mapping⁴² is employed to identify portions of the gait cycle that differ between groups and conditions.

Figure 4.

Biplane fluoroscopy images from a healthy control walking in a shoe and a carbon fiber ankle foot orthosis (AFO) from approximately 38% (top) and 72% (bottom) of stance. This proof-of-concept acquisition provides confidence that carbon fiber AFOs will not occlude bony geometry in biplanar fluoroscopic images.

Discussion

A better understanding of the effect of surgical correction and orthosis use on mobility, balance confidence, and lower gait biomechanics in individuals with neurodevelopmental disorders (e.g., associated with CMT or CP) can inform clinical decision making, advance ongoing AFO development, and provide quantitative evidence regarding OA development in these individuals. There is variation in orthotics services, and clinicians report problems with acceptance and use of AFOs amongst people with these conditions, possibly due to a mismatch between patient needs and device provision. An improved understanding of how and when AFO use by these individuals alters gait mechanics, physical mobility, and balance confidence will provide insight into potential mechanisms by which AFO use alters stability and balance. This has the potential to improve orthotic management and guide decision making on the potential gait, balance, and reduced fall risk following surgical care of patients with inherited neuropathies. Similarly, uncertainty remains regarding the specific effects of surgical management on gait and balance in individuals with foot deformity. This includes differing perspectives regarding optimal timing and type of surgical intervention, and objective guidance to ensure optimal alignment between patient needs and the surgical procedure is lacking. Systematic study of the effects of orthotic and surgical management in individuals with peripheral neuropathy and related foot deformity, within the context of developing clinical practice guidelines, has the potential to improve pain, gait, and mobility, reduce falls, and enhance overall quality of life.