Knee-ankle-foot orthoses (KAFOs) may serve many purposes for the pediatric patient. As with adults, KAFOs can provide support for weakness or mal-alignment of the lower extremity. Unlike adult applications, however, KAFOs have been shown to be effective in correcting deformity in the young, rapidly developing extremity such as in the treatment of tibia vara (Blount's disease). Although the use of KAFOs to reduce or even correct deformities is a benefit somewhat unique to pediatric practice, this article focuses on KAFOs prescribed for ambulation. The purpose is to critically review the existing literature on the use of KAFOs for the specific purpose of providing ambulatory potential in the pediatric or adolescent population who would otherwise remain non-ambulatory without this level of orthotic support.
KAFOs IN DUCHENNE MUSCULAR DYSTROPHY
Although KAFOs may be used for any number of pathologies affecting the motor control and stability of the lower extremities in children, the use of these orthoses in those with Duchenne muscular dystrophy has been studied more extensively than any other. Affecting only boys, Duchenne's is a muscle disease causing progressive weakness, especially in proximal muscle groups. Orthoses are typically considered in an effort to prolong ambulation once the child demonstrates the need for external assistance, such as when touching a wall or furniture is needed to maintain balance while walking. The age at which walking ceases in the absence of treatment is variable, ranging from 6 years 5 months to 13 years 7 months.1 Both ankle-foot orthoses (AFOs) and KAFOs can be indicated, based on the strength and resultant ambulatory ability of the patient. Orthoses may also be used in an attempt to control progressive contractures or to aid in diminishing muscle cramps.2 KAFOs are often used in conjunction with muscle releases to correct sagittal plane deformities, most commonly at the ankle such as Achilles tendon release or tenotomy.3 Release of the iliotibial band at the hip, as well as a posterior tibial-tendon transfer to correct varus of the foot and ankle, is also indicated for some patients.4 A program of postoperative physiotherapy and daily passive stretching were common in many of the studies that evaluated use of KAFOs in this patient population. Those that question the validity of pursuing this line of treatment that is aimed at prolonging ambulation have expressed doubts as to whether this ambulation is actually functional.5,6 Opponents suggest it is more responsible and beneficial to the patient and family to allow full time wheelchair use when functional ambulation is no longer possible, favoring the more practical wheeled-mobility and focusing on activities other than walking to facilitate other successes in life. That said, there is evidence in the literature that use of KAFOs in those with Duchene muscular dystrophy can prolong ambulation typically by at least 2 years as compared with those who utilize a wheelchair exclusively once independent ambulation without aids is no longer possible. Death by the age of 18 to 19 years of age is common, often due to pulmonary insufficiency, pneumonia, or cardiomyopathy.4
Bakker et al.3 performed a systematic review of the available literature on the use of KAFOs in those with Duchene muscular dystrophy. Their aim was to determine the level of evidence that exists to justify the use of KAFOs for ambulation in this population. The investigators reviewed the literature published in Dutch, English, French, or German for years 1966 to 1997. In their report published in 2000, 30 articles describing 35 studies met the criteria for inclusion. No randomized controlled trials were found, and 40 articles were excluded typically due to lacking sufficient data or outcome measures. Study designs were categorized as being either observational or case studies (n = 8), uncontrolled group studies (n = 23), or controlled group studies (n = 4). Identifying a total of 485 subjects treated with KAFOs, the age at which KAFO use began ranged from 6 to 17 years. There was significant variability with reported outcome measures. Most studies reported on “ambulation,” but there was frequently little description on how ambulation was defined. One of the better descriptions offered for the varying forms of ambulation in this population described KAFOs being used, chronologically, for independent walking (child is able to stand without support and able to walk without assistance), assisted walking (child is unable to maintain balance while standing and walking but can walk with somebody to steady him), attended walking (unable to stand without support or to progress when walking without much assistance), and standing with support in standing table for at least 2 hours).7 The diversity of outcome measures made it difficult to compare results across all studies. By using studies with sufficient data for review (n = 7), a percentage of success was calculated for those using KAFOs as the percentage of patients not completely wheelchair dependent after periods of 1 to 3 years. Wheelchair dependence was thought to be a reliably definable point in time, being the last point in which ambulation of any kind was reported. With this definition of success, those using KAFOs after 1 year of use had a median success value of 75.1% (range, 58.6%–92.8%), after 2 years of 47.9% (range, 22.7%–85.7%), and after 3 years of 24.3% (range, 4.5%– 29%). The median of the means for independent walking was found to be 24 months (range, 19.2–32.6 months); for assisted walking, 36.2 months (range, 0–90 months); and for standing ability, 50.5 months (range, 31.5–58.6 months). Use of KAFOs in this population was also cited as having a positive effect on controlling contractures, greater patient independence in both school and home without calling for assistance or needing a wheelchair, and other activities of daily living such as being able to play games, going to the blackboard, changing classes, and walking to places not as accessible by a wheelchair.4 One study8 demonstrated that boys who walked beyond the age of 13 were significantly less likely to develop a rapidly progressive scoliosis during the adolescent growth spurt as compared with boys who stopped walking at a younger age.
The potential for bias was considerable in many of the studies. Publication bias is a possibility with none of the studies being a randomized controlled study design. With just four studies being non-randomized controlled studies and most others being case reviews, there is a greater potential for published reports to reflect only the best results from varying forms of treatment. Patient selection bias was also possible in many reviews, in that frequently those patients reported on were those who were likely the most motivated to accept the necessary logistics to be fitted with KAFOs, not to mention commonly performed surgeries and physiotherapy. Last, the principle investigator in most reviews was also the treating physician or physiotherapist providing care to the enrolled subjects, which has the potential of introducing some forms of measurement bias. The potential for these biases in reporting simply suggest some conclusions should be read with caution.
In reviewing literature that spans over three decades, such as in Bakker's report, it is also important to take into account possible changes in technology. Only three studies in this review described use of what could be considered lightweight orthoses8–10 for the subjects reviewed. Thorough descriptions of orthotic design that could influence ambulatory performance, such as the alignments and/or immobilization of joints, were often lacking. For instance, only one report9 noted the angular position of the ankle (90 degrees) and the trimming of the plastic no more distal than the metatarsal heads. This is important because any residual static equinus or a rigid plastic extension beyond the patients' toes could slow forward progression of walking during the ipsilateral mid- and late-stance phases of gait. This, in turn, could cause a less energy-efficient gait pattern, which could ultimately have a negative influence on prolonging ambulation in a given subject.
Another point worth making with regard to orthotic design is the fact that all KAFOs were statically locked in extension, requiring the user to compensate with hiking of the pelvis or circumducting the leg on the ipsilateral side.11 Ambulating with both knees locked in extension has been shown to require significantly more energy than allowing knee flexion during gait in healthy subjects.12 Although this statically locked position is indicated in the absence of motor control for the various subjects reviewed with Duchene muscular dystrophy, some of the newer stance control knee joint designs available today may offer orthotic alternatives not possible in prior reviews.
The literature published to date for this population suggests that use of KAFOs can prolong assisted walking and standing, but the functionality of the walking that is prolonged is still uncertain. It also appears that the boys most likely to benefit are those with a relatively low rate of deterioration due to the disease process, are capable of enduring an operation, are well motivated, and have supportive caregivers.
USE OF KAFOs IN MYELODYSPLASIA OR OTHER FORMS OF PARAPARESIS
A relatively impressive amount of research has been conducted on the use of orthoses in children with myelodysplasia, including cases of paraplegia secondary to some form of spinal cord insult. Children with myelomeningocele (a form of myelodysplasia, which is also a form of what is known as spina bifida) are a very heterogeneous group of patients to study, due only in part to their functional levels of lesion that, in studies on ambulation, vary from thoracic level down to sacral lesions of the spine. There can be associated anomalies of the cerebellum and brain stem, such as Chiari malformations, hydrocephalus, and a wide range of spinal deformities. Most publications on the use of orthoses in this population are focused on those requiring more significant orthotic support. Several studies have been published on the use of reciprocating gait orthoses13–33 or hip guidance orthoses,34–40 commonly comparing each with other forms of hip-knee-ankle-foot orthoses (HKAFOs). Due to the nature of motor power that is affected in spinal cord lesions secondary to myelomeningocele, the use of KAFOs is much less common than other lower extremity orthoses. This is largely due to the spinal level in which quadriceps power becomes functional. For example, those patients with lesions in the thoracic or upper lumbar segments of the spine will lack strength in their hip flexors, extensors, adductors and abductors, as well as knee flexors, extensors, and motors across the ankle. This clinical picture requires orthoses above the hip to adequately control the lower extremities in relation to the torso for potentially functional ambulation. Moving caudally, a lesion of the mid-lumbar spine that is low enough to have more normal hip flexor power will also begin to have quadriceps power that becomes functional. Those with functional quadriceps power will typically also have both hip abductor and medial hamstring power, albeit often compromised, from which to recruit for potential ambulation. This small difference in lesion level is a significant leap in potential functionality due in large part to the functional strength of the quadriceps. Quadricep strength has been shown to be the single most important prognostic factor in achieving and maintaining ambulation in this population.41–44 As a result of these functional lesion levels, patients who have enough motor power to avoid the need for orthoses that cross the anatomical hip joint will frequently have the ability to ambulate with just AFOs, often with the use of upper extremity aids such as a walker or forearm crutches rather than KAFOs.
The use of KAFOs is typically reserved for those patients with lower lumbar lesion levels who demonstrate significant angular and torsional forces across the anatomical knee joint that are significant enough to cause concern for the overall health of the knee.45–47 To further illustrate the infrequency of KAFO use in this population as compared with various above hip (HKAFO, reciprocating gait orthosis [RGO], hip guidance orthosis [HGO]) or AFO orthoses, in their systematic review of the evidence in the literature on the efficacy of orthotic management of the lower extremities in children with myelomeningocele, Mazur and Kyle48 categorized patients treated for literature review into three groups: thoracic and upper-lumbar level, described as those requiring a parapodium, ParaWalker (HGO) RGO or HKAFO; low lumbar level, described as those requiring AFOs due to lack of strength in hip extensors, ankle plantarflexors, and ankle dorsiflexors; and sacral level, where typically a foot orthosis is all that is required due to weak intrinsic foot muscles. In this comprehensive literature review, not a single manuscript was found on the use of KAFOs in this patient population.
Despite there being little mention of KAFO use in this population in the literature, and no publications found that report on the efficacy of this modality of orthotic management, some important points can be made in the context of this review. Research on the impact of AFOs on gait patterns in those with a lower lumbar or lumbosacral lesion level46,47,49–52 raise some interesting and important points to consider with regard to a potential rationale to brace above the knee but staying distal to the hip. Williams et al.53 conducted a retrospective review of 72 adult patients with myelomeningocele who were community ambulators and reported 17 (24%) had what was described as significant knee symptoms. The authors cited that in those with low lumbar lesions, even though their quadriceps strength is often grade 4 or higher, no good solution exists for the lack of hip abductor power these patients often need to overcome. This lack of hip abductor power can cause a patient to have a significant posterior-lateral abductor lurch during the stance phase of gait.52 This gait pattern, in turn, can cause an abnormal valgus stress across the knee joint.46 The medial and anteromedial rotary instability is thought to contribute, especially when combined with the presence of fixed flexion deformities, to eventual degenerative changes of the knee.53
Thomson et al.47 evaluated the effect of AFOs on the ankle and knee in children with myelomeningocele, using three-dimensional gait analysis. The authors reported significant improvements in sagittal plane function with reductions in excessive ankle dorsiflexion, which also translated into reductions of crouch and knee extensor moments in those with low lumbar lesion levels. There was, however, a concerning increase in transverse plane knee motion in stance that actually worsened while ambulating with AFOs compared with barefoot gait. The authors stated that transverse plane motion was a result of the reduction in motion at the ankle in combination with the fixed foot progression in stance with simultaneous lateral trunk shift required during stance to compensate for weak hip abductor musculature. They postulated that this excessive knee transverse plane rotation may contribute to knee instability, more so than any coronal plane abnormalities. It was also pointed out that those patients with sacral level lesions failed to demonstrate any biomechanical benefit of AFO use. On the contrary, these patients demonstrated the increased transverse plane knee rotation coupled with a reduction in power-generating capabilities of the ankle. The latter is especially detrimental to these patients because it diminishes their ability to recruit triceps surae power that is present due to the more caudal lesion level. These studies suggest that more research is needed on not only determining the most effective way to combat the abnormal forces that can act upon the knee—both with and without use of an AFO—but also to identify those patients who might potentially benefit from KAFO use in hopes of preventing debilitating knee pain later in life.
Some authors have suggested that KAFOs can be useful in patients with low lumbar lesion levels secondary to myelomeningocele to prevent recurrent falls and possible knee effusions,45 or in the presence of a knee valgus thrust.47 Although an argument can be made for this prescription rationale in clinical practice, there is no evidence in the literature that demonstrates the efficacy of KAFOs used for these purposes. The forces acting on the knee joint in these patients are typically not a true valgum force in the coronal plane but rather a much more complex series of abnormal forces from multiple planes of motion. These forces are exacerbated by the abductor lurch gait pattern previously described, which may be compounded by the presence of increased pelvic motion in both the coronal and transverse planes.54 There is, therefore, a need to determine whether these abnormal stresses crossing the anatomical knee joint could truly be reduced with a KAFO in these patients. Surgical attempts to strengthen abduction power through muscle transfers were found to not abolish the abductor lurch gait pattern.16,52,55 Improvements in KAFO design to make them more comfortable and acceptable to the patient is another avenue of potential research and development.56 In everyday practice, this is a significant challenge in that even if prognostic factors for degenerative changes of the knee could be established, let alone addressed by orthotic means, those patients who have the ability to function with just AFOs are unlikely to agree to KAFO use when they are pain free as community ambulators at a young age.
USE OF KAFOs IN OSTEOGENESIS IMPERFECTA
Osteogenesis imperfecta (OI) is a rare genetic disorder associated with a broad spectrum of musculoskeletal manifestations. Frequently referred to as “brittle bone disease,” it is associated with bowing and fractures of the long bones of the extremities, muscle weakness, ligamentous laxity, and varying degrees of spinal deformity.57 The most referenced classification system for OI was developed by Sillence,58 describing four types: patients with Type I are described as having the greatest potential for normal function; Type II patients are the most severe, rarely surviving their first year of life; Types III and IV, from a functional standpoint, are the most similar but their level of function is highly variable. Those patients with Types III and IV OI are more likely to require orthoses. Not all patients with Type III or IV OI will ambulate. One report found that independent sitting by 10 months of age was a predictor for functional ambulation.59 Seventy-six percent of 51 patients surveyed walked as their primary means of mobility, whereas less than 1 in 5 of those who did not meet this milestone reported ambulation as their primary means of mobility.
Use of orthoses is common in ambulatory patients with OI. Most of these patients require orthotic protection of the long bone structures and support crossing all joints of the lower extremity for ambulation; i.e., HKAFO.60–64 For those who do achieve ambulation, the advantages offered by thermoplastic materials in orthotic design for more total contact, compressive control of the long bone segments, such as used in fracture bracing,65 are consistently noted in publications on the orthotic management of OI. Orthoses are frequently used in conjunction with intramedullary rodding of the tibiae and femurs in children and was described by one author as “the single most important determinant in extending the time period between procedures.”60 Although proper external support of the lower extremities was identified as being, “of equal or greater importance than the surgery itself,” no real data were provided in this report to support these claims. The need for frequent surgical revisions of intramedullary rodding secondary to the patient outgrowing the fixed-length fixation of the long bone was significantly reduced through the introduction of an extensible rod, as described by Bailey and Dubow.66 This development allows longer-term use of orthoses between potential surgical revisions in the growing child.
The most comprehensive study found, albeit a small sample size, in this review was a prospective, randomized crossover trial on the effects of withdrawing use of orthoses in matched pairs of children with OI.67 In a collaborative effort among the US National Institutes of Health, the Children's Hospital National Medical Center and an orthotist experienced in the molding and fitting of orthoses for those with OI, 10 patients, each having either Type III or Type IV OI, were paired for age and clinical severity. Motor strength, the frequency of fractures, and independence in daily activity were assessed every 4 months over a 32-month period. Instrumented gait analysis was also performed during braced and unbraced periods. The study aimed to better determine the benefits and risks of maintaining or discontinuing use of orthoses in those who demonstrated the ability to ambulate with HKAFOs. The 10 patients were selected from a population of 75. Each was at least partially ambulatory, had been braced for at least 2 years, and was fracture free for at least 3 months before enrollment into the study. The ages of those who met the criteria for inclusion ranged from 3 to 8 years. One member of each patient pair wore orthoses for 16 months, whereas the other did not. The braced and unbraced groups were then crossed over for a second 16-month period. Relevant data were prospectively collected every 4 months throughout the study. A 5-point scale was developed to rank clinical status, stamina and functional independence, and each child was assessed by the same physical therapist. The same orthotist fitted each subject with custom orthoses, lightweight thermoplastic designs with bivalved, total contact thigh sections, medial and lateral knee joints, and articulated ankle joints offering free sagittal plane motion. Drop locks at the hip or knee were used for increased stability when indicated.
Many trends were reported, but no clinical findings were found to be statistically significant, thought to be due largely to the small sample size. The authors reported that in this small sample size of patients, the children were less sedentary, participated in more upright activities, and were more functionally independent when braced. There were 17 lower extremity fractures during the unbraced period, compared with 8 during the braced period (p = 0.06). Only one child had no fracture during the study period. One child fractured during the braced period but not the unbraced period, whereas three children fractured during the unbraced but not the braced period. With regard to gait analysis findings, the largest and most consistent finding among the subjects was increased hip flexion in late swing phase, which also equated to a larger stride length while walking in the HKAFOs compared with being unbraced. Finally, the authors reported that many parents and children “felt more secure” with the orthoses on, which in turn, provided more psychological confidence in a willingness to allow the child to participate in more fully upright activities.
The use of KAFOs in pediatric patients is more often applicable to individual patient circumstances rather than patient populations, based on pathology. The need for orthoses to be adjustable for growth and other changing anatomical alignments is a factor skilled orthotists must consider while treating children and adolescents. As efforts to quantify the potential benefits of KAFOs in these patients are made, it is also important to understand that children are not little adults. Healthy children walk more slowly, with shorter stride lengths, higher cadence, and with less energy efficiency than adults.68 Further, the existing data on “normals” for children and teens to serve as potential controls in future studies are still developing, and categories of age ranges are frequently broad. Future studies aimed at creating a body of evidence on the usefulness of KAFOs in this population will need to consider at least some, if not all, of these factors to advance clinical practice in both clinically relevant and scientifically valid ways.
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