Linked Hip-Knee-Ankle-Foot Orthoses Designed for Reciprocal Gait
James H. Campbell, PhD, CO
Two fundamental mechanical designs of linked hipknee-ankle-foot orthosis (HKAFO) systems have been developed; both use a simple lateral weight shift from one limb to the other as the basis for orthoticassisted reciprocal gait. The hip guidance orthosis (HGO or ParaWalker) was developed at the Orthotic Research and Locomotor Assessment Unit1–4 and the reciprocal gait orthosis (RGO) was developed at Louisiana State University (LSU).5 Both systems were designed for patients with highlevel spinal cord dysfunction (congenital or traumatic) who would not otherwise be candidates for ambulation. The similarities and differences in the design and use of these orthoses have been the focus of intense research in the last decade.
HIP GUIDANCE ORTHOSIS
Whittle and Cochrane6 suggest that the most important design aspect of the HGO or ParaWalker is its rigidity in single limb support, which enhances the patient's ability to clear the contralateral limb as it advances in swing. The work of Jefferson and Whittle7 demonstrates that in an HGO, the lower limbs remain essentially parallel in the coronal plane, providing for better ground clearance of the limb in swing.
The HGO enables patients with paraplegia to walk independently with a reciprocal gait pattern.8 Theoretically, this orthosis also reduces the energy cost of walking because the patient does not have to lift body weight off the ground, as is necessary with a swing-through gait using conventional HKAFOs and crutches. Studies that compared the physiologic cost of walking in the HGO and conventional HKAFOs in children with myelomeningocele demonstrated an 87% increase in gait speed and 10 beats per minute reduction in heart rate when using the HGO.4 Watkins et al.8 report that the HGO works effectively to enable individuals with complete thoracic level spinal cord injury to undertake therapeutic walking, based on approximately 200 fittings of the orthosis. The HGO system has also been successful in adult patients with complete spinal cord lesions ranging from C-8 to T-12 levels, with more than 85% of those fitted with an HGO continuing to use their orthosis on a regular basis at the 20-month follow-up interview.9 Many who learn to use an HGO achieve independent use of the orthosis and low energy ambulation indoors and outdoors and on a variety of floor or ground surfaces.
The HGO was originally developed for children with myelomeningocele. The goal of the HGO is to provide the opportunity for functional independent ambulation. Rose et al.4 define three criteria for independent orthosis-supported ambulation for these children. First, energy cost must be low at a reasonable speed of ambulation (30% to 60% of normal speed for the child's age-matched peers). Second, the child must be able to transfer independently from sitting (chair) to walking and vice versa. Third, the child must be able to don and doff the orthosis independently, within a reasonable amount of time, without unreasonable effort. Researchers at the Orthotic Research and Locomotor Assessment Unit tracked 27 children who had used the HGO for at least 6 months to evaluate the outcomes of its use.4 Their work has identified that stability of the trunk (the ability to sit with the arms raised above the head for a prolonged period without support) is an important predictor of HGO success. The HGO is able to provide, at low energy cost, reciprocal ambulation for children with low thoracic and high-level lumbar lesions. Twenty-five of 27 children had to be upright in another orthosis before using an HGO. Only 2 of 27 (7.6%) children had scoliosis.10 Further work is required to investigate whether this extraordinarily low incidence of scoliosis is related to the use of an HGO or a conventional HKAFO.
RECIPROCAL GAIT ORTHOSES
Douglas et al.5 describe the LSU RGO as a lightweight bracing system that gives structural stance phase support to the lower trunk and lower limbs of the patient with lower extremity paralysis; it uses a cable-coupling system to provide hip joint motion for swing phase. In the RGO, via its cable system, flexion of one hip (in swing) results in extension of the other hip (concurrently in stance). The hip joints of the orthosis are coupled together using two Bowden cables to transmit the necessary forces (although the original design used a single cable, functional problems and subsequent revisions evolved into the use of a second cable). This reciprocal coupling has the added benefit of eliminating simultaneous hip flexion and reducing the risk of "jackknifing" during ambulation. Studies using the RGO for patients with a variety of neuromuscular disorders)5,11 and report that long-term bracing with RGO, and the early ambulation this makes possible, decreases the potential for development of secondary deformity. In a group of 100 adults with paraplegia fitted with an RGO, seven were able to ambulate 100 feet with no more than two 30-second rest periods. For many patients, up to 45 hours of training were necessary to achieve functional gait with an RGO. Although the RGO has clearly been shown to be an effective intervention for reciprocal gait in adults and children with paraplegia, some extravagant claims about its success have resulted in uncertainty about prescription criteria.12
The RGO was initially designed to afford an upright posture and reciprocal gait pattern for children with myelomeningocele and has been used routinely for such patients during the past 20 years.13 Little has been published, however, to substantiate its effectiveness for this group, and it is reasonable to suggest that considerably more attention has been given to its suitability for the adult paraplegic population than to the group for whom it was designed. Yngve et al.14 analyzed the effectiveness of the RGO in children with myelomeningocele who had absence or weakness of the hip extensor mechanism. Patients ranged in age from 18 months to 15 years. The function and potential benefit of three configurations of the reciprocating mechanism were evaluated. In the first configuration, ambulation was tested with the reciprocating mechanism engaged to allow hip flexion with contralateral hip extension. The first configuration represents the normal settings for the RGO. In the second configuration, the reciprocating mechanism was released to provide free flexion and extension at the hips, representing a conventional HKAFO with unlocked hip joints. In the third configuration, the hip joints were locked to eliminate hip motion, representing a conventional HKAFO with restricted hip motion.
Each child ambulated at his or her maximum velocity for 15 to 31 m in each of the three configurations. The distance the child walked was determined by individual strength and ability. The number of steps taken and the time to complete the distance were recorded, and velocity and step length were calculated. Although 17 children were included in the study sample, gait characteristics of only 8 children were analyzed. In five of these eight children, gait speed was significantly faster in the RGO than in the other configurations. It is important to note that 75% of the children in the sample had motor function at the L-3 level and that only 18% had complete paralysis of hip musculature. The authors also did not provide information about how and why data from a subsample were used in analysis. Given these concerns, it is not possible to draw any meaningful conclusions about function and neurosegmental level while a patient is wearing an RGO.
McCall et al.15 fit a group of 29 children with neurologic deficiencies (age range, 1 to 16 years) with the RGO at Shriners Hospital, Shreveport Unit, in 1981 and 1982. They report that the RGO offered improved standing and ambulatory potential in these neurologically deficient children while preventing development of deformity and increasing patient independence. Mazur et al.16 further investigated differences in functional characteristics of reciprocal gait and swingthrough gait, using the technology of a gait laboratory. In a sample of three children with thoracic level myelomeningocele, reciprocal gait with an RGO was modestly more efficient than a conventional HKAFO.
Guidera et al.,17 in a retrospective review, evaluated the long-term usage pattern of patients fitted with reciprocating gait orthoses at the Shriners Hospital for Crippled Children in Tampa, Florida. Twenty-one children (13 boys, 8 girls; mean age, 8.75 years) were reevaluated 2 years after receiving their RGO. Nine of the children had thoracic level lesions with no active hip flexion; 12 children had lumbar level lesions. All of the children had required surgical correction of lower limb or spinal deformities before or during the bracing period, and 17 exhibited residual contracture. Eleven patients required additional orthotic support of the spine. When questioned about their use of the RGO, all patients reported problems with donning and doffing, wear and tear on clothing, heat, having multiple repairs, and down time. Almost half of the children were still using the RGO, but only four were community ambulators. The RGO was typically used at school rather than at home. The authors examined energy efficiency of three patients who used the RGO consistently. All were more energy efficient, and two were faster with a swing-through gait pattern as compared with the reciprocating pattern. Despite this, patient preference was to reciprocate.
Guidera et al.17 then evaluated various factors that may contribute to the long-term success or failure of the RGO. Discontinuance occurred more often in children with a thoracic level lesion, in the presence of obesity, when there was a lack of patient or family support, and if the patient had spinal deformity, mental retardation, knee flexion contracture of more than 30 degrees, or hip flexion contracture of more than 45 degrees. Other negative factors included spasticity, trunk and upper extremity weakness, asymmetric hip dislocation or motor function, and lack of prior standing or walking in a parapodium or other type of orthosis. These factors, especially in combination, have an adverse impact on long-term use and effective ambulation in an RGO.
Rogowski et al.,18 at Newington Children's Hospital, evaluated the outcomes of fitting with RGOs for children with thoracic and high lumbar level of paralysis. They were especially interested in the criteria or indicators for fitting with an RGO, as well as the use and acceptance of the orthosis, using data from 48 consecutive cases fit between 1982 and 1991. The average time spent in the orthosis for their sample was 6.3 hours a day. Many of the children in the Newington study discontinued brace use between the ages of 7.5 and 11.5 years. In this study of children with paraplegia, the most important determinants of RGO use were age and level of paralysis.
OTHER TYPES OF RECIPROCAL GAIT ORTHOSES
The advanced reciprocating gait orthosis (ARGO) developed by Hugh Steeper Limited of London, is best described as a modified LSU RGO. A single push-pull cable links the mechanical hip joints. The most appreciated improvement reported by investigators who have examined this design is the ease it confers on rising from a sitting position and on sitting down again after standing. This improvement is the result of a cable link between orthotic hip and knee joints and the addition of pneumatic struts to assist knee extension. The arrangement assists patients in standing directly from a sitting position in which the knees are typically flexed, without prior manual straightening and locking of the knees.
The isocentric reciprocating gait orthosis (IRGO) is a further modification of the LSU RGO. In this variant, the two crossed Bowden cables are replaced by a centrally pivoting bar and tie rod arrangement.
COMPARISON OF THE HGO AND THE RGO
The focus of comparative studies has been to compare orthoses in terms of energy expenditure with orthosis-assist ambulation. Varying designs of orthoses are capable of affording reciprocal gait patterns to both adult and pediatric paraplegics; the important variable is functional outcome, best evaluated by energy-expenditure studies.
Relative oxygen cost (mL/kg/M) was compared in five paraplegic subjects,19 four children and one adult, while wearing an RGO and HGO while ambulating. An oxylog was used to record oxygen consumption while the subjects ambulated during steady-state. Although all of the subjects trained and used the orthoses for varying amounts of time, the trend from these data shows that the HGO provides a more energy-efficient gait. On average, the oxygen cost while using the HGO was 27% less than that of the LSU RGO. The reductions in oxygen ranged from 12% to 42%. Following this trend of great efficiency, the subjects ambulated, on average, 33% faster with the HGO than with the LSU RGO. These preliminary results indicate that the HGO appears to be a more efficient orthosis for level ambulation in the paraplegic population.
In 1989, the Department of Health and Social Security in the United Kingdom commissioned an extensive comparative trial of both orthoses.6,20 The trial took almost 2 years and was completed at the Nuffield Orthopaedic Centre, Oxford, England. Eighteen male and four female paraplegic subjects used each orthosis for 4 months in a crossover study. Clinical, ergonomic, biomechanical, psychological, and economic assessments were performed at appropriate stages on each patient who completed the trial. Fifteen subjects were able to use both orthoses, five were unable to use either, and two succeeded with the HGO and not the LSU RGO. At the end of the trial, 12 subjects chose to keep the LSU RGO, four the HGO, and six neither.
Those choosing the LSU RGO preferred its appearance; those choosing the HGO preferred its speed of donning and doffing. Jefferson and Whittle7 commented that intersubject differences were much greater than interorthosis differences, but the biomechanical assessments demonstrated that the patterns of movement were not identical in the two orthoses. No children were used in this study, despite the fact that both systems were designed for the pediatric paraplegic patient. It is not therefore possible to draw conclusions relative to either system in the pediatric patient population.
COMPARING HGO, LSU RGO, AND ARGO
Biomechanical analyses were done on three orthoses in terms of general parameters and movement of the lower limbs and pelvis.7 This single case study was of an adult paraplegic who was a proficient user of all three systems. The subject for this study was a 33-year-old man with a traumatic T5 complete lesion. Comparison was made among the HGO, the LSU RGO, and the ARGO.
In terms of general gait parameters, the differences among the orthoses are small; this conclusion was reached using measurements taken from videotape and VICON data. Relative to pattern of movement, this study reported stride length in orthoses to be similar, a smaller range of pelvic motion in the HGO, and a more fluent gait in the HGO. Analyses of hip joint motion in the sagittal plane indicated that the major difference in hip joint motion is the smaller degree of hip extension in the HGO.
Analyses in the coronal plane and the observation that hip abduction in the HGO is greater than that in the RGO is important. In the HGO, the lower extremities remain essentially parallel, making it easier to clear the ground. The pattern of gait was best with the HGO, that with the LSU RGO being slightly better than the ARGO. The main advantage of the ARGO was the greatly improved ease of standing up and sitting down.
This study concentrated on objective measurement in a single case study. It is one of few attempts to establish a theoretic base on which to base orthotic prescription for this patient group; the conclusions reached are therefore important.
COMPARING LSU RGO AND IRGO
A study21 examined the energy cost of walking in four subjects using the LSU RGO and the IRGO. In this study, the physiological cost index (PCI) was significantly lower during ambulation trials with the IRGO compared to the LSU RGO. This was the only measurement that detected a significant difference between the two designs. Other variables, such as gait velocity, cadence, and step length, were similar in both braces. The methods, testing procedures, and data analysis used for this study suggest that PCI can be used as a sensitive indicator of gait efficiency in spinal cord injury subjects. It is not possible to make definitive conclusions that are based on such a small sample size regarding the relative benefit of one design over another. For example, it is not clear whether the reported advantages related directly to replacing the cables or whether the increased rigidity of the IRGO contributed directly to the reduction in the PCI.
For children and adults with paraplegia resulting from more significant neuromuscular system impairment, evidence suggests that the HGO/parawalker provides better ground clearance and a smooth gait pattern than a conventional HKAFO. These benefits are possible because of the mechanical rigidity of the orthosis; however, they are achieved only with significant cosmetic deficit. In many instances, the improved cosmesis of the RGO is much preferred by patients. The mechanical reliability of the RGO, however, has been questioned in the literature. In more recent developments, an advanced reciprocating gait orthosis design enhances the patient's ability to stand up and to sit down without having to lock or unlock orthotic knee joints. The isocentric reciprocating gait orthosis attempts to combine the mechanical advantages of the HGO with the cosmetic and therapeutic advantages of other RGOs. Perhaps the most important finding across the studies comparing RGOs and HGOs is that in terms of general gait parameters, the differences among all the contemporary orthotic options are small.
Despite the considerable activity and associated expense within this subject area, research and clinical experience indicate that most individuals with paraplegia opt for wheelchair mobility after discharge to the community because this provides a faster, safer, and more practical means of mobility with considerably less energy expenditure.
The ability to walk remains an important objective for many children who are paraplegic, as well as for their parents. The ability to reach the goal of functional ambulation depends on many factors, including the cause of the paraplegia, the level of the neuromuscular lesion, the presence of hydrocephalus, the strength of the upper limbs, the availability and effectiveness of parental support, and the child's own coordination and motivation. The ability to ambulate is also dependent on the prescription and fitting of an appropriate orthosis. The literature indicates that contemporary forms of orthotic management, specifically the HGO and the RGO, improve function for many children with paraplegia. This claim is consistent with this author's research and clinical experience.13
What remains unclear, however, is the influence of these accepted designs on the development of joint contracture and the progression of deformity. The problem of progressive deformity in children with paraplegia is significant. Often a spinal deformity appears within the first decade and progresses to skeletal maturity; the most common deformity is an increased lumbar lordosis. For children with a neurologic level of lesion at T-12 or higher, the incidence of spinal deformity is almost 100%. The impact of fitting of an HKAFO, especially of the HGO and RGO, on the prevention of spinal deformity requires much more scholarly attention and study.
Correspondence:James H. Campbell, PhD, CO, Becker Orthopedic, 635 Executive Drive, Troy, MI 48083; e-mail: Beckerjimc@aol.com .
JAMES H. CAMPBELL, PhD, CO, is affiliated with Becker Orthopedic, Troy, Michigan.
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