In considering the individual recommendations, the reader should recognize the complex interactions between the numerous variables that ultimately influence the effect of AFOs on balance. Every treatment decision requires consideration of the patient's individual diagnosis and presentation, the balance-related tasks that will be of greatest importance to that individual, and the resultant design characteristics of the prescribed AFO. In the research environment, this is further complicated by the need to select an outcomes assessment methodology to ultimately determine the impact of the intervention. The interplay between these four domains is multifaceted. One of the challenges to future research will be to variously control these different considerations to a level where the impact of a given physical deficit or AFO design characteristic on balance during a given task type can be better understood. As such, although research recommendations were organized into the four illustrated domains, the reader will notice considerable overlap between the various domains for a given recommendation.
AFOs should be individually designed according to a patient's physical presentation and their specific functional needs, many of which are balance related. For example, one patient may require an orthosis to aid in transfers, another patient may benefit from the reduced cognitive load while walking, and a third patient may benefit from the improved postural control in his or her wheelchair. As clinicians consider their treatment recommendations for patients with a defined set of physical deficits, a better understanding of the effects of various design characteristics across a broader spectrum of functional activities is needed.
RECOMMENDATION 1: IMPROVE THE VALIDITY OF THE INVESTIGATED TASKS TO EVERYDAY LIFE ACTIVITIES
To better understand the immediate effects of AFOs on balance, research designs and methods should better imitate or simulate real life environments, tasks, and experiences. Thus, in addition to flat, even surfaces, the effects of AFOs on gait should be examined while walking on uneven terrains, inclines, and declines, while negotiating stairs and in crowded areas. In addition to gait considerations, the effects of AFOs should be examined during activities requiring both static and dynamic balance control such as transferring and reaching events.
RECOMMENDATION 2: CONSIDER THE INFLUENCE OF THE AFO DESIGN ACROSS MULTIPLE TASK DOMAINS
A given AFO design may provide an individual with improved balance in one task while compromising balance in another. The limitations, advantages, and disadvantages of various AFO design characteristics across multiple task domains should be more clearly defined to aid in clinical decision making.
RECOMMENDATION 3: ANALYZE THE EFFECT OF AFO DESIGN CHARACTERISTICS ON BALANCE STRATEGIES AND RECOVERY
The ankle and hip strategies of balance control have been well defined and examined in motion analysis laboratories. Questions exist about the effects of different AFO design characteristics on these strategies. To what extent are these strategies compromised or assisted? When balance compromise does occur, are patients still able to adequately recover? Are specific patient populations more prone to the disruption of balance strategies with the presence of an AFO? What compensatory strategies are available to patients when using AFOs of various designs? Are certain design characteristics more conducive to the maintenance of hip and/or ankle strategies? An increased understanding in this area will allow clinicians to better tailor their treatment plans toward the balance needs of individual patients.
RECOMMENDATION 4: IDENTIFY THE COMPENSATORY VALUE OF “ABNORMAL” MOTIONS FOR BALANCE CONTROL INVOLVED IN SPECIFIC TASKS
In the presence of neurologic, orthopedic, or motor deficits, patients often develop abnormal compensations that facilitate better balance control and stability. In such cases, it may be more beneficial for an orthotic intervention to “optimize” rather than “normalize” the in-brace kinematics of the individual. The role of these various compensations in preserving balance and stability across various task types requires more investigation. Similarly, the ability of AFOs to enhance or compromise these compensations requires greater understanding.
RECOMMENDATION 5: EXAMINE THE INTERACTION BETWEEN AFOS AND ASSISTIVE DEVICES
Often, an orthosis is prescribed with the use of a cane or walker. The use or disuse of such assistive devices may affect the dimensions of the base of support, the location of the center of mass, and the proprioceptive inputs available to the patient, all of which may bear on the balance implications of the prescribed AFO. A greater understanding of these interactions may be instructive.
Orthotists use specific AFO design features to influence desired biomechanical function. These design features include material properties and their associated stiffness, tibial alignment relative to the floor, the presence or absence of articulations along with any resistance or stops associated with the articulation, joint alignments and positions, footplate characteristics, trimlines, and the number and type of closures used. The clinical utilities of these design features, as they relate to balance, require further clarification.
RECOMMENDATION 6: EXAMINE HOW VARIABILITY IN ANKLE JOINT MOTION AND RESISTANCE INFLUENCES BIOMECHANICAL FUNCTION AND BALANCE
AFOs may eliminate, restrict, assist, or allow joint motion according to joint inclusion, material selection, and trimlines. In closed chain kinematics, the amount of ankle flexibility affects the timing and position of the tibia and, by association, the alignment of the knee and the hip. In open chain kinematics, joint biases can serve to preposition the limb for weight acceptance. The impact of ankle motion on balance across various patient presentations and during various tasks requires further clarification.
RECOMMENDATION 7: IDENTIFY THE AFFECT OF THE FLOOR-TO-TIBIA ANGLE ON STATIC AND DYNAMIC BALANCE CONSIDERATIONS
The floor-to-tibia angle influences the forward progression of the tibia during stance phase with further implications at more proximal joint segments. The relative degree of this angle is currently based on clinical evaluation with consideration to the preservation of forward momentum in walking, protection of proximal joint structures, available range of motion across lower limb joint segments, and available lower limb strength and endurance. Further research is required to aide in the determination of the most appropriate floor-to-tibia angle for the preservation of both static and dynamic balance across commonly encountered tasks and terrains.
RECOMMENDATION 8: CONSIDER FOOTWEAR CHARACTERISTICS AND THEIR EFFECTS ON BALANCE CONTROL
The footwear characteristics most likely to alter the influence of an AFO are heel height and sole alterations. The heel height directly affects the tibia-floor angle and the considerations described earlier. Similarly, the sole may or may not be rockered, flared, or wedged, all of which may influence stance phase dynamics during gait and static standing balance. These considerations are included in this section as a reminder that studies performed with AFOs must clearly report the footwear used during their evaluations and consider their influence on final outcomes.
RECOMMENDATION 9: EXAMINE THE INFLUENCE OF VARIOUS PLANTAR SURFACES MODIFICATIONS ON BALANCE CONSIDERATIONS
Somatosensory influence on balance is well recognized. The ability to alter this influence by modifying the plantar surface characteristics of an AFO is unknown. Do alterations of plantar surface contours significantly alter pressure distribution? Do these changes equate to differences in limb awareness? Is balance affected by the use of total contact principles at the foot and ankle as might be obtained with molded inner boots? Is there a beneficial affect to vibratory stimulation at the plantar surface of the foot and if so, for which patient populations? Does habituation to these external stimuli occur? The effect of these plantar surface modifications on balance is currently unknown.
RECOMMENDATION 10: DETERMINE HOW THE WEIGHT OF THE ORTHOSIS AFFECTS DYNAMIC BALANCE
The effects of the weight of AFOs on dynamic balance are currently unknown. Although the benefits of a lighter weight device for subjects with lower limb weakness are reasonably presumed, the potential value of a heavier device with its associated influence on lower limb proprioception and general limb awareness have not been explored.
In addition to the types of tasks a subject engages in and the characteristics of the AFO they may be using, the impact of AFO interventions on balance variables will be further affected by the severity and type of the subject's functional impairments. The relative risk of compromising balance across various patient populations and physical presentations is unknown. Variables such as spasticity, joint contracture, weakness, and fatigue may affect the interactions between the orthotic intervention and balance considerations. Therefore, future research must also consider the type and severity of physical impairments present in their subjects.
RECOMMENDATION 11: CONSIDER ENDURANCE LIMITS AS THEY RELATE TO BALANCE COMPROMISE, WITH AND WITHOUT THE USE OF AN AFO
Fatigue and compromised endurance are commonly encountered in many patients managed with AFOs. These factors may increase fall risk, compromise both static and dynamic stability, and encourage activity restriction. The degree to which an AFO of a given design may reduce or augment fatigue levels during both static and dynamic tasks is currently unknown and requires further consideration.
RECOMMENDATION 12: EXAMINE THE INTERPLAY BETWEEN SENSORY COMPROMISE AND PROPRIOCEPTION AND AFO INTERVENTIONS
The ability and mechanisms by which AFOs may affect balance variables in the presence of sensory compromise are largely unknown. The interplay between proprioceptive and mechanical influences also requires further investigation. In addition to refining the AFO characteristics that may be most appropriate for subjects with sensory-motor compromise, such insights would inform on the potential value of AFO interventions in patients with sensory compromise only.
RECOMMENDATION 13: EVALUATE THE VARIABLES OF SPASTICITY AND RANGE OF MOTION RESTRICTIONS AS THEY PERTAIN TO THE POSSIBLE EFFECTS OF AFOs ON BALANCE CONTROL
Orthoses are often prescribed for both contracture management and to optimize alignment as it pertains to limb spasticity. In such cases, balance may be considered a secondary consideration. The interplay between these physical restrictions, the resultant AFO recommendations and the subsequent balance effects require further understanding.
RECOMMENDATION 14: EVALUATE THE EFFECTS OF AFOs ON BALANCE IN CHILDREN, YOUNG ADULTS, AND ELDERLY ADULTS
Many of the patient populations in question present with underlying balance deficits. The addition of AFOs may accommodate or aggravate these deficits. A patient's ability to compensate for these deficits may be related to their age, with younger subjects demonstrating an improved ability to adapt to the imposition of external influences about the lower limb. A better understanding of the developmental stages of balance control and the ability of older subjects to adapt to both balance deficits and AFO interventions is needed.
Balance control of the body is complex and difficult to quantify. Similarly, the resulting symptom of imbalance can affect many aspects of an individual's function, confidence, and societal participation. As research into the possible effects of AFOs on balance continues, consideration must be given as to how to best assess the influence of AFO interventions on balance as it pertains to functional abilities, self-confidence, and activity levels. To this end, future research needs to assess the impact of AFOs across a broad spectrum of outcome domains.
RECOMMENDATION 15: EXAMINE TO WHAT EXTENT AFOs MAY AFFECT BALANCE CONFIDENCE AND SOCIETAL PARTICIPATION
Balance can be assessed with quantifiable laboratory techniques and with patient-derived data and activity monitoring. Future research should collect and consider patient feedback as it relates to balance confidence with and without the AFO interventions. Similarly, efforts should be made to monitor both activity levels and societal participation with and without interventions, based on the assumption that these will correlate well to balance improvements.
RECOMMENDATION 16: CONSIDER THE IMPACT OF AFOs ON THE COGNITIVE LOAD AND STABILITY
When balance deficits are present, increased cognitive demands are required as patients conscientiously monitor and maintain their balance. To the extent that an intervention improves balance, these cognitive demands may be reduced. Dual task protocols are well developed and could be used successfully to examine the degree to which AFO's use may positively or negatively affect the cognitive loads associated with balance control.
RECOMMENDATION 17: WHERE POSSIBLE, ESTABLISH A RELATIONSHIP BETWEEN QUANTIFIABLE LABORATORY BALANCE ASSESSMENTS AND PATIENT DERIVED DATA
Although laboratory balance assessment methods are well established, their correlation to patient confidence, societal participation, activity levels, and fall rates are unclear. Relationships between the observed effects of AFOs on standardized laboratory techniques should be correlated to more clinically relevant assessment measures.
RECOMMENDATION 18: ASSESS THE EFFECTS OF AFOs ON POSTURAL STABILITY IN INDIVIDUALS WITH UPPER MOTOR NEURON DYSFUNCTION WHO ARE RESTRICTED TO WHEELCHAIR USE
There is anecdotal evidence regarding the effectiveness of AFOs on sitting posture, trunk control, and upper limb function for individuals who are restricted to wheelchair use because of whole body neuromuscular impairment. Further understanding about the interaction between the positioning of the lower limbs and the ancillary effects cited earlier is needed.
RECOMMENDATION 19: DEVELOP BLINDING TECHNIQUES FOR RESEARCH DESIGNS
Future research designs should include methods to reduce rater and user bias. Although blinding of participants is often impossible, blinding of the rater could be simply and reasonably performed. Development of other blinding techniques could improve the validity of research studies.
RECOMMENDATION 20: DEVELOP OUTCOMES ASSESSMENT TOOLS TO ASSESS BALANCE CONTROL OF INDIVIDUALS WITH VARIOUS LEVELS OF FUNCTIONAL IMPAIRMENT
Currently, the ceiling and floor effects of commonly used clinical outcome measures limit our understanding of the impairments observed in the most and least affected subjects. This limits the general understanding of intervention effectiveness in these populations. Because the range of clinical pathologies requiring AFOs is quite broad, appropriate outcome measures are not always available. There is a need for more assessment tools that are validated for and tailored to the physical abilities of the various patient populations encountered to reduce floor and ceiling effects and better inform the effect of AFOs on balance factors.
ENHANCING THE CLINICAL RELEVANCE OF FUTURE RESEARCH
In addition to the recommendations discussed earlier, additional considerations were emphasized in the conference proceedings to further enhance the clinical relevance of future research.
GREATER DESCRIPTIONS OF AFO INTERVENTIONS ARE NEEDED IN FUTURE RESEARCH PUBLICATIONS
Research articles using orthoses should clearly describe the factors related to the material properties, material stiffness, mechanical joint, footplate characteristics, shank-to-foot angle, trimlines, closures, and associated footwear. The AFOs should be fitted by a qualified orthotist and should be optimized for the patient with the optimization methods clearly described. In addition to the description of the physical properties of the device, the time provided for acclimatization to the device and the rationale for selecting that time should be considered and described. These efforts will enhance the clinical relevance of future research findings.
GREATER UNDERSTANDING AND UTILIZATION OF CLINICALLY RELEVANT OUTCOME MEASURES ARE INDICATED FOR RESEARCHERS AND CLINICIANS ALIKE
Clinically assessable outcomes measures can quickly define a subject's functional presentation and reaction to a given intervention. Their use in future research translates those efforts into a metric that is better understood and appreciated by clinicians, patients, and pay sources alike. Likewise, clinicians who familiarize themselves with these assessment tools will better appreciate future research findings and correlate those findings with daily patient care.
AFOs are designed, in part, to meet the individual balance and stability needs of a given patient. In determining the design characteristics of an AFO intervention, clinicians must consider both the physical impairments of the subject and the various tasks they will most frequently encounter. There is a complex interplay between these variables indicating a need for more research findings to aid clinical decision making.
Historically, AFOs have largely been evaluated according to their ability to impact gait parameters and maintain range of motion in the presence of neuromuscular compromise. There is a growing recognition that these parameters are insufficient and that greater attention needs to be placed on the positive and negative effects that these intervention can have on balance parameters across a range of activities and tasks outside of level ground ambulation.
Ultimately, very little is known about how orthoses influence balance. More literature is needed as clinicians increasingly consider the impact of AFOs on such things as static and dynamic balance, balance confidence, and overall activity levels. To aid in the translation of literature findings to clinical application, the methodologies should include detailed descriptions of the interventions such as the physical properties of the AFO, footwear, and acclimation periods used. Further, to the extent that research findings are correlated to clinically viable assessment techniques, their findings will be more readily appreciated and incorporated into clinical settings.
Keywords:© 2010 American Academy of Orthotists & Prosthetists
ankle-foot orthoses; balance; research