Whether questions occur informally or through the use of an existing survey instrument, patient feedback can properly identify what tasks are considered most relevant to the daily lifestyles. This information should be weighed and incorporated in the decision-making process as it relates to design and alignment of an AFO.
CENTER OF MASS
The ability to maintain upright posture and balance during standing and walking is dependent, in part, on the location of the body's COM relative to the center of pressure (COP) in standing and the location of the body's COM relative to the advancing limb during walking.6–8
In standing, balance is often reflected by the location of the body's COM and regulated through movement of the COP under the feet.9 As the COM moves (accelerates), the COP has been reported to act almost instantaneously10 to maintain the position of the COM. Forward and backward movement of the COP in the sagittal plane is controlled by ankle dorsiflexion and plantarflexion moments while lateral and medial movement of the COP in the coronal plane is controlled by abduction and adduction moments across the hip. This continuous interplay between COM movement and COP regulation to maintain the body's COM within the base of support enables the ability to perform static activities safely and effectively.
The balance requirements during walking are different then for those of standing. Although standing balance requires that the COM fall within the area of the feet, during walking, the COM will frequently and regularly strays outside of this area. For example, in preswing, the COM is considerably anterior to the foot. According to Winter et al.,10 during ambulation, we are in a continuous state of imbalance, and the only way that we can prevent falling during walking is to position our swinging foot ahead of and lateral to the forward-moving COM.
The addition of pathologic conditions such as stroke, traumatic brain injury, spinal cord injury, multiple sclerosis, peripheral neuropathy, cerebral palsy, and spina bifida can impose even greater demands on the control system of posture and balance. Depending on the type of pathologies involved, different elements of this control system may be either impaired or absent, disrupting the body's ability to monitor and regulate the location of the body's COM. When this happens, individuals may attempt alternative balance strategies but ultimately find themselves at an increased risk of balance compromise and falling.
When strategies to monitor and maintain the position of the body's COM are compromised, a person may benefit from an AFO designed to restore proper location of the body's COM. In doing so, the practitioner should look not only at the alignment of the lower limb but also at its ultimate effects on overall posture and balance.
AFO design typically includes such variables as material selection, footplate length/stiffness, ankle configuration (e.g., articulation, solid), and footwear considerations. Each of these can ultimately affect the ability of the device to impact balance and stability. For example, materials that are too stiff may unnecessarily limit existing functional motion leading to an inability to adapt to disruptions in balance. Conversely, a material that is too flexible may provide inadequate structural support.
Footplate length and stiffness represent another design consideration. A full, stiff footplate may allow the COP to move more anteriorly both in static standing and the mid stance phase of ambulation, facilitating a knee extension moment in both scenarios. Conversely, an AFO design may require a more flexible footplate or three-quarter length footplate to facilitate metatarsal phalangeal extension during the preswing phase of gait. Depending on the patient's presentation, any of these design variations maybe indicated. However, balance considerations should influence these treatment decisions.
Although the sagittal alignment of the ankle in the AFO is an important design consideration, it is the angle that results from the AFO/footwear combination that should be regarded as the key element for standing and walking balance. Specifically, the resultant tibial “shank vertical angle” (SVA), defined as the angle formed between the tibial shank and the floor, has been shown to modify both kinematics and kinetics to approximate normal standing and walking.11,12 When the necessary range of motion is present, SVA alignment can occur by selecting an appropriate dorsiflexion angle for a solid device or by adjusting the position of joint stops in an articulated device. In the absence of available range of motion, modifying the SVA can be achieved by manipulating the heel/sole differential of the footwear itself or by including a heel lift between the AFO and the footwear. This effectively changes the sagittal alignment of the SVA relative to the floor.13,14
Although it is difficult to determine how changes to the SVA affect the specific location of the COM and COP in a clinical setting, there are factors that can influence their relative location and that should be assessed during the initial fitting of the AFO/footwear combination. The SVA should be evaluated relative to2 the floor,3 knee and hip joint alignment,4 femoral shank alignment,5 trunk and head alignment,6 and overall postural alignment. Changes or “fine tuning” of the AFO/footwear combination and resultant SVA can exhibit immediate alignment changes that improve balance as seen in the following case.
A boy with a diagnosis of lipomyelomeningocele presented with weakness of the left limb and relative sparing of the right limb. For the left limb, the MMT was remarkable with motors distal to the knee presenting with either 0/5 or 1/5. Proximal to the knee, the quadriceps and hamstrings were 4/5 and the gluteus maximus and hip abductors at 3/5. Without orthotic management, the patient exhibits the following gait deviations:
- Excessive left knee flexion in stance
- Valgus stress at the left knee in stance
- Lateral trunk lean
- Left foot/ankle hyperpronation
- Ipsilateral drop of the pelvis
- Increased hip and knee flexion during swing phase on the contralateral limb
The patient wears a custom-molded solid AFO with carbon fiber reinforcement, full length footplate, and AFO ankle angle (tibia-foot) set at 90°. The patient is a community ambulator both with and without the AFO, but in the absence of the AFO, the patient complains of fatigue and instability and exhibits increased stance phase knee flexion on the left limb.
During the initial fitting, the AFO was put in his existing shoes with relatively no heel-sole differential, which placed the tibial SVA at 90° relative to the floor. The resultant alignment placed the ground reaction force well anterior to the knee, causing a knee extension moment and compensatory hip flexion. This resulted in the COM and COP being moved too far forward (Figure 3). In this condition, the patient reported that it was difficult to balance and sometimes had to shift body weight to the less effected limb. During walking, the patient exhibited increased knee hyperextension in stance and a greater forward trunk lean during stance phase. The patient complained of discomfort around the posterior aspect of the left knee.
The same patient's existing shoes were removed, and a different set of shoes was provided to improve the SVA. The new shoes included an existing heel-sole differential that caused the SVA to be inclined forward. The result was that the ground reaction force was aligned more appropriately to the knee joint center, which reduced the knee hyperextension moment and compensatory hip flexion (Figure 4). Furthermore, the forward trunk lean was reduced bringing the COM back to a better location for the patient. It is likely that the COP was also affected by the change of location of the COM and moved more posteriorly along the plantar aspect of the AFO's footplate. The patient reported that it was easier to balance and that he felt more stable while walking. The patient also indicated that the discomfort across the knee was absent.
This example can be replicated with the “fine tuning” of the AFO/footwear combination for the spina bifida, cerebral palsy, and stroke populations, or indeed for any population in which the desired SVA cannot be obtained through manipulation of the ankle angle alone because of range of motion restrictions. When the SVA is inadequately inclined forward, these populations routinely exhibit a forward trunk lean and anteriorly displaced COM. This is especially injurious to the balance of patients presenting with hip extensor weakness such as might be commonly observed in the spina bifida and multiple sclerosis populations as they are unable to counter the flexion moments generated at the hip. For patients with upper motor neuron dysfunction, such as cerebral palsy and stroke, the forward trunk lean and anterior displacement of the COM may aggravate a primitive reflex pattern, further engaging already over active hip extensors. Anecdotal experience suggests that the restoration of the proper COM position can result in improved balance and stability.
It is important that COM and COP cannot be neglected when providing an AFO. Although difficult to determine in the clinical environment, these variables can be approximated and manipulated by the AFO/footwear combination and the resultant SVA alignment. Whenever possible, patient feedback should be solicited to ensure the preservation or restoration of balance and stability.
Fatigue has generated much debate over the years15 with uncertainty as to how to properly “define” and “measure” the concept.15,16 To fully address the topic is well beyond the scope of this article. Therefore, the discussion will address several key features that should bring a greater awareness to the concept of fatigue as it relates to balance and orthotic treatment.
Much of the empirical and observational evidence seems to suggest that fatigue is a phenomenon of the muscle and as such will be described as “muscle fatigue” hereafter. Beyond that distinction, it is difficult to identify a suitable and agreed on definition. Therefore, the following considerations are listed to present a more balanced description of muscle fatigue:
- Muscle fatigue is a point in time when muscle contraction can no longer be maintained.17
- It occurs at the point in time when the desired force and power output can no longer be maintained during repetitive submaximal muscle contractions.17
- Motor unit recruitment and derecruitment may help to sustain target force output.18
- Failure point is a function of both physiologic and psychologic factors, but it is difficult to discretely discern casual relationships.18
- The ability to identify events leading up to the failure point of muscle fatigue may have clinical significance in its prediction and the identification of treatment strategies.18
In considering these different concepts, the time-dependence of muscle fatigue is quite relevant19,20 and must be transferred to the clinical setting if it is to be appropriately managed. A patient's immediate short-term performance in a controlled clinical setting may not be representative of their stamina and endurance in real world environments and activities. Thus, observational gait analysis across a limited number of steps on a level walkway may not provide the practitioner with enough information to reflect the true relative risk of muscle fatigue across the major muscle groups of the lower limb and their implications on balance and well being. This can ultimately lead to poor decision making regarding orthotic treatment.
Fatigue at most of the major muscle groups of the lower limb will have balance implications. Of greatest concern are the following: dorsiflexor fatigue increases the risk of failed swing phase clearance with an increased risk of falling. It may also compromise the ankle strategy during static reaching events where controlled plantarflexion is needed to retain stability. Plantarflexor fatigue may permit increasing crouch during gait and ultimately knee buckling. It may also compromise the ankle strategy of balance maintenance during tasks involving forward reaching. Muscle fatigue at the extensors of the knee and hip increases the risk of anterior knee instability and associated falls. Finally, hip flexor fatigue may directly affect the ability of the patient to generate enough forward momentum to achieve swing phase clearance, predisposing the patient to an increased risk of trips and falls.
The effects of muscle fatigue and the ability of AFOs to compensate for such deficiencies are not always immediately apparent. As an example, Geboers et al.21 reported that individuals with lower motor neuron ankle paresis failed to demonstrate significant improvements while performing a 10-m walking test with and without AFO interventions. However, improvements with the AFOs did approach significance during both a combined-cognitive assessment and a 6-minute walking test. Patient-derived data suggested positive effects with both walking performance and walking effort while wearing AFOs. Thus, among this cohort, the effects of the AFOs were not fully appreciated until matters of fatigue and endurance were engaged.
To fully appraise a patient's relative risk of balance compromise because of muscle fatigue requires some means of assessment in a clinical setting. When muscle fatigue is suspected, based on knowledge of the existing condition, several assessment strategies are available including soliciting self-report data, MMT, and longer duration timed walking tests.
As discussed earlier, patient reporting can provide rich information that can assist with decision making about orthotic treatment. In this case, questions should be time and task centered (Table 2). When asking these questions, it maybe helpful to use proxy terms for “fatigue” that a patient may understand or respond to more easily such as “get tired,” “loose your balance,” and “become unstable.” It is important that these questions are defined in terms of both time and task to more fully appreciate a patient's functional limitations. It is not uncommon for fatigue-related balance deficits to come forward in this type of patient report that might not otherwise be immediately apparent during the patient assessment. This type of feedback can be extremely useful when creating a treatment plan.
Although the information derived from MMT provides limited immediate appreciation of muscle fatigue, a full assessment can identify muscle groups where fatigue may be suspected. For example, a muscle group with a grade of 4/5 in a limb where most muscle grades are 5/5 may be less prone to fatigue as the patient can adequately compensate for these deficiencies. In contrast, the muscle grade of 4/5 may be more concerning in a limb where surrounding muscles are comparatively weaker. In this event, the original muscle may be frequently recruited for stability and compensation and thus, at greater risk for premature fatigue. In such instances, a longer duration muscle test or targeted questioning is warranted.
As suggested earlier, standardized outcome measures have also been developed to measure a subject's relative endurance. These measures involve sustained physical exertion and are best represented by several timed walking tests, with the 2- and 6-minute test commonly used.22 It is important to remember that the duration of the timed event must be sensitive enough to detect the suspected muscle fatigue.
Muscle fatigue can have a dramatic impact on an individual's balance, function, activity, and safety. Clinical assessment of fatigue may include standardized walking tasks or manual muscle tests but are largely determined through patient feedback. The clinician's ability to identify balance compromise because of fatigue will facilitate the design of more appropriate AFO interventions.
AREA OF CONTACT
Another factor that seems to influence balance positively or negatively is the geometry of a person's base of support. During standing, this is the area contained between both feet as they contact the ground.23 This base of support can also be expanded during both standing and walking with the utilization of a cane or a other assistive device. However, in cases where musculoskeletal deformity is present, the base of support can also be reduced significantly. This occurs as a product of reductions in the available area of contact of the distal limb segments with the supporting surface. In practical terms, the area of contact refers to the amount of the plantar surface of the foot, AFO, or footwear that is in contact with the ground. Interventions that restore or broaden this area of contact improve the geometry of the base of support, thereby augmenting balance and stability.
An example of a compromised area of contact can be seen in the affected foot of some hemiplegic gait patterns. Because of the compromised cortical control of the tibialis anterior during swing phase, attempts to dorsiflex the foot for clearance may only translate to inversion of the foot. The position of the inverted foot will sometimes persist into early stance phase where only the lateral border of the foot is contacting the ground, significantly reducing the area of contact at this point in gait. This reduction to the base of support, combined with the undesirable moments generated by ipsilateral overactive hip adductors is disruptive to balance, creates varus instability at the ankle and places the subject at an increased risk for falling.
When range of motion is available, the area of contact, in this case the full plantar aspect of the foot, can be restored using an AFO to correctly preposition the foot. This kinematic correction allows the patient to contact the ground through a larger surface area, restoring a more physiologic base of support during this phase of gait. Similar area of contact deficits include both equinus and calcaneal gait, both of which may be treated after a similar fashion by restoring or enhancing the available area of contact.
When range of motion restrictions prevent the full restoration of the area of contact through an AFO alone, deficits can be addressed by manipulating the design characteristics of the AFO's plantar surface, in the form of sagittal and coronal accommodative wedges. In other instances, the area of contact may be enhanced through the use of shoe options and designs such as lateral shoe outflares and medial shoe stabilizers. These types of modifications, made in conjunction with the external support of an AFO, can address malalignment issues in both the sagittal and coronal planes that would otherwise disrupt balance and generate harmful valgus, varus, or hyperextension forces across the knee of the affected limb.
In some cases, the restoration of a broader area of contact may be sufficient to restore balance and stability. In other instances, it maybe one of the several factors that must be addressed to adequately impact balance and stability. In either case, the area of contact should be evaluated and considered to determine its level of compromise and whether an appropriately designed AFO can restore or improve its geometry.
The sensory system is comprised of visual, vestibular, and somatosensory components. All are important for the maintenance of balance and play a role in proprioception or the body's awareness of its own position in space. The complexities of proprioception are important to consider when it is absent or impaired as the effects can profoundly disrupt balance and stability.
Basic testing for deficits in proprioception usually involves an assessment of joint position with eyes alternately open and closed. This is commonly assessed during upright posture using the Romberg test.24 A person's ability to maintain their balance with their feet together and eyes open, only to loose their balance when their eyes are closed equates with positive test for proprioceptive compromise.
Things to consider when attempting to provide proprioceptive feedback through the medium of an AFO include compression from the orthosis and/or accompanying elastic garment, the weight of the orthosis and/or shoe, and weight distribution of the AFO/footwear combination. The ability of an AFO to bypass areas of sensory disruption and restore some level of proprioceptive feedback is treated independently, later in these proceedings.
The use of weight or weight distribution to enhance proprioceptive input should be used with caution as it can create other issues of instability, particularly in the presence of motor weakness. However, in some cases, the additional weight of an AFO seems to engage the more proximal, less affected joint receptors to provide additional feedback, and a better awareness of the limb in space.
A dramatic example of this phenomenon was observed in the recent treatment of a patient with impaired proprioception. The patient required new shoes and specifically requested heavy work boots. According to the patient, the heavy work boots gave him a better awareness of where his feet were during standing and walking and provided better overall stability. When the same person was provided athletic shoes that weighed less then his work boots, the individual began to ambulate with what had the appearance of an ataxic gait pattern. According to the patient, he had no real sense as to where his limbs were during gait, and this significantly impaired his balance. Moreover, the patient conveyed that many tasks during the day were difficult to accomplish and required greater concentration.
Impairments to proprioception represent a difficult problem that is best addressed with a team approach. It requires deliberate attention during the patient evaluation to identify the manifestations of the impaired proprioception and to determine which orthotic strategies may be useful in helping to improve balance.
OPTIMIZING ACTIVITIES OF DAILY LIVING
The effectiveness of AFOs has been historically assessed according to their ability to “normalize ambulation.” However, clinical experience suggests that this goal may be unattainable for some patients and of lesser importance for others. As discussed earlier, the effectiveness of an AFO can only be optimized when the patient's individual needs and treatment priorities are assessed fully. Areas of function outside of the normalization of gait that may benefit from the provision of appropriately designed AFOs include the “optimization” of gait, reaching activities, transfers, and supplementing seating systems.
For many patients, the goal of “normalizing” ambulation is a reasonable one. However, in many other cases, weakness, joint contracture, and pathology preclude the realization of this objective. In such cases, attempts to normalize ambulation may only serve to further disrupt it and reduce activity levels. This is particularly concerning when attempts at “normalization” result in balance compromise and increased fall risk. Such misplaced expectations will often result in noncompliance with the orthosis.
Importantly, these patients can and do find compensatory mechanisms that, while not “normal,” permit the functional performance of daily encountered activities. In such cases, treatment can be tailored toward the “optimization” of these compensatory mechanisms to enhance the available function. Two examples will illustrate these principles.
Duchenne muscular dystrophy is characterized by progressive muscle weakness and joint contracture along with distinctive compensatory strategies to maintain balance and functional ambulation. These strategies include posterior trunk lean, knee hyperextension, and toe walking.25 The normalization of gait would suggest that attempts should be made to restrict the atypical plantarflexion seen in this population. However, in the context of this pathologic presentation, the excessive plantarflexion represents a necessary compensation for severe weakness of the dystrophic knee extensors. The provision of a “normalizing” AFO would render the patient's compensatory strategies ineffective, further disrupt balance and likely eliminate functional gait. In such cases, the patient is better served by a treatment strategy intended to “optimize” balance and alignment within the limitations of the pathologic presentation. This can be done by foregoing day time AFOs and permitting active plantarflexion in standing and gait while using AFO night splints to discourage the further progression of plantarflexion contracture.
In the presence of prolonged knee extensor weakness, such as might be seen in postpolio and multiple sclerosis, patients will often compensate for their weakness through relative hyperextension of the knee. A normalizing AFO would be designed to limit available plantarflexion and by association, knee hyperextension. However, within the confines of the described presentation, the suggested treatment plan is likely to place unreasonable demands on compromised knee extensors, resulting in sagittal instabilities and either disuse of the AFO or the self-imposed activity restriction. A second treatment approach would be to appreciate the value of the knee hyperextension to the balance and stability of the patient and seek to “optimize” these compensatory kinematics rather than “normalize” them. Thus, an AFO that restricts end range hyperextension while permitting sufficient motion to retain sagittal knee stability might be recommended.
Although the “normalization” of gait is a reasonable goal for many patients treated with AFOs, others will be better served through a careful consideration of their current compensatory mechanisms and a treatment plan designed to “optimize” rather than “normalize” their performance.
Reaching activities represent a host of commonly encountered ADLs. Because of the dynamic effects of such activities on the location of the COM, their performance requires that the patient be able to adapt their posture to accommodate changes in COM location. In many instances, these adaptations occur through the so-called ankle strategy, which may or may not be compromised by the presence of an AFO and the relative restrictions it places on movements in the sagittal. Particularly, in cases where balance compromise and general weakness are a concern, consideration should be given to the effect of the AFO design on the patient's ability to perform reaching tasks. Just as observational analysis is used to validate the effects of an AFO and gait, clinicians may choose to administer a Functional Reach Test with and without the intervention to ensure that this important ADL category is not precluded in the presence of the AFO.
Transfers are another important consideration in the performance of many ADLs in both independent and fully dependent patients. These include the transitions from sitting to standing, standing to sitting, and the exchange of sitting surfaces. As with reaching activities, balance during transfers is facilitated by the patient's ability to manipulate the location of their COP in response to movement of the COM during these activities. For many patients with profound motor control compromise or weakness, transferring activities and associated mobility may be a more relevant concern than ambulation. In such cases, consideration should be given to the design elements of the AFO that might facilitate these transfer events for patients and assisting caregivers alike.
SUPPLEMENTING SEATING SYSTEMS
Individuals with neuromuscular presentations that require the use of a seating system often have difficulty with sitting balance and the associated variables of upper limb control and dexterity. Attention to the position of the head and trunk relative to the pelvis can help to reestablish better balance. However, the benefit of proper foot/ankle alignment is often overlooked. Although the mechanisms are not fully understood, experience suggests that when the foot/ankle is properly positioned in the AFO and the AFO is properly positioned on the footplates of the seating system, sitting balance can be improved. This can result in decreased posturing of the upper limbs to maintain balance and improvements in task specific reaching activities.
Realistically, most patients will identify multiple relevant ADLs and functional tasks that are important to their individual situations. The challenge for the practitioner is to determine how best to prioritize and address those various needs by optimizing the design characteristics of the AFO. In cases where the AFO will only address certain needs it is important that this be conveyed to the patient, so that realistic expectations are established. The ability of a properly designed pair of AFOs to enhance ADL performance outside of normalized walking is illustrated later.
This patient is a 22-year-old woman with a diagnosis of spastic diplegic cerebral palsy. Because of gastrocnemius contracture, she is only able to achieve full knee extension when the ankles are plantarflexed 5°. Without orthotic management, the patient ambulates with a crouch gait pattern, hyperpronation across the foot and ankle, and bilateral toe out. She requires a rolling walker to assist with ambulation whether using her AFOs or not. The patient was fit with and is currently wearing bilateral solid AFOs set in accommodative plantarflexion with external heel wedges to address the area of contact deficiency and incline the SVA to improve standing and walking balance. With the AFOs, the patient's crouch gait pattern is reduced during standing and walking (Figure 5).
The patient was asked to complete the 16-item Activities-specific Balance Confidence Scale26 to determine her confidence in here abilities to maintain her balance during common ADLs with and without the AFOs. The level of confidence is rated from 0% (no confidence) to 100% (full confidence) for each activity with higher scores indicating a greater balance confidence.
The patient's Activities-specific Balance Confidence score without her AFOs is reported at 26%. With the AFOs, her reported confidence improves to 60%. Improvements in balance confidence were particularly striking for several items. Confidence in the ability to walk up and down a ramp without loosing her balance or falling improved from 10% to 90%. Similarly, confidence in her ability to maintain her balance if she was bumped by people in a crowded mall environment improved from 10% to 80% with the use of her AFOs. Finally, the patient's reported confidence in her ability to walk outside of her house to a car parked in the driveway improved from 30% to 90% with the use of her AFOs.
In addition to improvements in balance confidence, the patient also reported that with the AFOs, she was able to walk for longer distances and did not fatigue as quickly as she did without the AFOs. She also indicated that the ankle angle alignment of previous AFOs was typically set at 90° and made it difficult to achieve a more erect posture during ambulation. Overall, the patient feels that the AFOs have made a dramatic improvement in her balance, function, and stamina.
The use and effectiveness of an AFO to address imbalance and associated functional deficits remains a complex issue and is dependent on many factors. These range from the design and alignment of the AFO to the severity of the underlying deficit. Decision making about treatment for balance should include factors related to COM, fatigue, area of contact, proprioception, activities outside normalized ambulation, and patient expectations. Each requires thoughtful consideration to optimize and tailor treatment to meet the balance needs of patients and ultimately improve the quality of life.
1. Whiteside S, Allen M, Barringer W, et al. Practice Analysis of Certified Practitioners in the Disciplines of Orthotics and Prosthetics
. Alexandria, VA: American Board for Certification in Orthotics and Prosthetics Inc.; 2007:1–33.
2. Bleck EE. Orthopedic Management in Cerebral Palsy. Clinics in Developmental Medicine No 99/100.
London: Mac Keith Press with Blackwell Scientific Publications Ltd; 1987:98–285.
3. Gage JR. Principles of treatment in cerebral palsy. In: Gait Analysis in Cerebral Palsy.
Oxford, UK: Blackwell Scientific Publications Ltd; 1991:118–119.
4. Dedding C, Cardol M, Eyssen IC, et al. Validity of the Canadian Occupational Performance Measure: a client-centred outcome measurement. Clin Rehabil
5. Malec JF. Goal Attainment Scaling in rehabilitation. Neuropsychol Rehabil
6. Winter DA. Human balance
and posture control during standing and walking. Gait Posture
7. Adamczyk PG, Kuo AD. Redirection of center-of-mass velocity during the step-to-step transition of human walking. J Exp Biol
8. Chastan N, Westby GWM, Montcel STD, et al. Influence of sensory inputs and motor demands on the control of the centre of mass velocity during gait initiation in humans. Neurosci Lett
9. Winter DA, Patla AE, Prince F, et al. Stiffness control of balance
in quiet standing. J Neurophysiol
10. Winter DA, Patla AE, Frank JS. Assessment of balance
control in humans. Med Progress Tech
11. Owens E. “Shank Angle to Floor Measurers” and Tuning of “Ankle-Foot Orthosis Footwear Combinations” for Children With Cerebral Palsy, Spina Bifida and Other Conditions
[MSc thesis]. Glasgow: University of Strathclyde; 2004.
12. Meadows CB. The Influence of Polypropylene Ankle-Foot Orthoses on the Gait of Cerebral Palsied Children
[PhD thesis]. Glasgow: University of Strathclyde; 1984.
13. Owen E. A clinical algorithm for the design and tuning of ankle-foot orthosis footwear combinations (AFOFCs) based on shank kinematics. Gait Posture
14. Owen E. Proposed clinical algorithm for deciding the sagittal angle of the ankle in an ankle-foot orthosis footwear combination. Gait Posture
15. Bigland-Ritchie B. Muscle fatigue
and the influence of changing neural drive. Clin Chest Med
16. Vollestad NK. Measurement of human muscle fatigue
. J Neurosci Methods
17. Ratel S, Duché P, Williams CA. Muscle fatigue
during high-intensity exercise in children. Sports Med
18. De Luca CJ. The use of surface electromyography in biomechanics. J Appl Biomech
19. Gandevia SC. Neural control in human muscle fatigue
: changes in muscle afferents, motoneurons and motor cortical drive. Acta Physiol Scand
20. Parijat P, Lockhart TE. Effects of quadriceps fatigue
on the biomechanics of gait and slip propensity. Gait Posture
21. Geboers JF, Wetzelaer WL, Seelen HA, et al. Ankle-foot orthosis has limited effect on walking test parameters among patients with peripheral ankle dorsiflexor paresis. J Rehab Med
22. Kosak M, Smith T. Comparison of the 2, 6, and 12-minute walk tests in patients with stroke. J Rehabil Res Dev
23. King MB, Judge JO, Wolfson L. Functional base of support decreases with age. J Gerontol
24. Lanska DJ. The Romberg sign and early instruments for measuring postural sway. Semin Neurol
25. Segal IM. Management of musculoskeletal complications in neuromuscular disease: enhancing mobility and the role of bracing and surgery. Phys Med Rehabil
26. Miller WC, Deathe AB, Speechley M. Pyschometric properties of the Activities-specific Balance
Confidence Scale among individuals with a lower-limb amputation. Arch Phys Med Rehabil
Keywords:© 2010 American Academy of Orthotists & Prosthetists
balance; function; AFO; fatigue; center of mass; proprioception