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Effect of Knee Orthoses on Hamstring Contracture in Children With Cerebral Palsy: Multiple Single-Subject Study

Laessker-Alkema, Kristina PT; Eek, Meta Nyström PT, MD

doi: 10.1097/PEP.0000000000000267
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Purpose: To examine the effect of knee orthoses on extensibility of the hamstrings in children with spastic cerebral palsy (CP).

Methods: The short-term effects of knee orthoses on passive range of motion (ROM), spasticity, and gross motor function of the hamstrings. Ten children with spastic CP, aged 5 to 14 years, at Gross Motor Function Classification System levels I to V, were followed. The orthoses were worn for a minimum of 30 minutes day, 5 days per week, during the intervention period of 8 weeks.

Results: Visual analysis using the Two Standard Deviation Band Method supported improvements in passive ROM for all 20 hamstring muscles and in 12 of 14 knee extension measurements. Analyses with the Wilcoxon signed rank test confirm the individual results and support a significant increase in hamstring muscles (P = .005) and knee extension (right: P =.028; left: P =.018) compared with baseline.

Conclusions: In children with spastic CP, 8 weeks of treatment with knee orthoses can improve extensibility of the hamstrings.

This study examined the short-term effects of knee orthoses on hamstrings extensibility in children with spastic cerebral palsy.

Habilitation & Health, Habilitation—Child and Youth (Ms Laessker-Alkema), Kungälv, Region Västra Götaland, Sweden; and Department of Pediatrics (Dr Eek), Institute of Clinical Sciences, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.

Correspondence: Kristina Laessker-Alkema, PT, Habiliteringen Kungälv, S‐442 37 Kungälv, Sweden (kristina.alkema@vgregion.se).

Grant Support: This study was supported by grants from the Regional research board at Västra Götaland, Sweden, the Petter Silfverskiöld Memorial Foundation, the Norrbacka-Eugenia Foundation, National Association for Disabled Children and Youths (RBU), and the Folke Bernadotte Foundation.

At the time this article was written Kristina Laessker-Alkema was a student at Sahlgrenska Academy, Institute of Neuroscience and Physiology, University of Gothenburg, Gothenburg, Sweden.

The authors declare no conflicts of interest.

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INTRODUCTION AND PURPOSE

Cerebral palsy (CP) describes a group of permanent disorders of the development of movement and posture, causing activity limitations that are attributed to nonprogressive disturbances that occurred in the developing fetal or infant brain.1 The majority of people with CP have a spastic syndrome. In children with CP, the muscle tone as measured with the Ashworth scale increases up to 4 years of age and then decreases up to 12 years of age. The same tendency is seen in all spastic subtypes.2 Spasticity can interfere with body function, mobility, positioning, and self-care. It often results in impaired longitudinal muscle growth, which can lead to decreased range of motion (ROM), contractures, and progressive musculoskeletal deformities.3 Mechanisms of muscle contracture in children with CP are unclear, and clinical research evaluating the effects of stretching is inconclusive.4 Physical therapy plays a major role in the treatment of children with CP and is aimed at the prevention of consequences to abnormal muscle tone, treatment of muscle and joint deformities, and reduction of cognitive and sensory disorders.5 Stretching programs are an important component of physical therapy intervention within this group of children. It can be performed passively, by another person, or actively; the child initiates and maintains the stretch. Prolonged positioning is used to achieve a longer-duration stretch of a particular muscle or muscle group. Casts, splints, and orthoses are all devices that are designed to keep the body in a certain position to achieve prolonged stretch.6

The decreasing range of joint motion caused by insufficient muscle length is a common problem in children with CP, often worsening with age.7 Hamstrings are a group of muscles involved in hip and knee motion and function and as the hamstrings extend across both the hip and knee joints; contraction of the muscle would apply movement on the 2 joints simultaneously. Decreased ROM in the hamstrings may cause several problems related to body function and structure and is one factor contributing to the deterioration of functional skills, such as walking, standing, and sitting.7

There is a clinical impression among physiotherapists that stretching and the use of orthoses help prevent contracture in children with CP. But although orthotic management in children with CP is widely applied, little is known about the efficacy of this treatment, and there is an ongoing discussion whether stretching is effective. Two reviews support limited evidence that manual stretching can increase ROM, reduce spasticity, or improve walking efficiency in children with spasticity.8,9 Prolonged stretching was preferable to improve ROM. The research in this area is, however, weak because of methodological issues, small sample sizes, and a small number of studies.

Prolonged stretch can be applied by the use of orthoses or by serial casting. Most published studies focus on the ankle joint. In periods when ankle-foot orthoses are used, passive ROM increases compared with periods during which the orthoses are not used,10 or stays unchanged during intervention compared with a decrease after nonintervention periods.11 Casting used alone, or in addition to injections of botulinum neurotoxin A,12 supports that casting improves passive and dynamic ankle dorsiflexion in the short term. Only a few studies have been published that have attempted to examine the effect of stretching on the knee and hip in children with CP. These studies had few participants and used various methods, making it difficult to draw any definite conclusions. Static weight-bearing in a standing frame can increase length of the hamstrings in nonambulant children with CP,13 and serial casting can improve passive ROM around the hip and knees in children with CP.14 Two studies evaluated the effectiveness of inflatable splints and reported significant improvements in the hip and knee.15,16

Knee orthoses for stretching is an easy and relatively inexpensive method compared with casts or positioning in standing frames. The purpose of the present study was to examine the efficacy of knee orthoses on extensibility of the hamstrings in children with spastic CP.

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METHODS

Participants

Children, aged between 1 and 16 years, with bilateral spastic CP in 1 county rehabilitation center were included in the study. Inclusion criteria were increased muscle tone in the lower extremities associated with restricted ROM in the hamstring muscles, based on critical values for passive joint ROM from the national surveillance program for cerebral palsy, CPUP.17 Children were excluded if they had had botulinum neurotoxin A injections, orthopedic surgery in the lower extremity musculature, or a treatment period with knee orthoses during the past 6 months. Possible participants were contacted through the child's regular physiotherapist.

The Regional Ethics Review Board at the University of Gothenburg approved the study. Written informed consent was obtained from each child's parents.

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Procedures and Measures

A multiple, single-subject study design was used.18 The baseline period lasted 2 weeks and the intervention period 8 weeks. In single-subject design, each participant serves as her or his own control, which involves multiple, repeated observations. Each child was evaluated 7 times during the baseline period, once a week during the intervention and directly after the period by the research physiotherapist. The following outcomes were evaluated to determine whether there were significant changes after the intervention: passive ROM in the hamstrings and knee extension, muscle tone, and gross motor function.

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Range of Motion

Passive ROM was measured with a hand-held plastic goniometer with the child in the supine position, with the head in midline and the arms by the side of the body. ROM was measured with a scale divided at intervals of 1°. Extensibility of the hamstrings was measured with the tested hip passively flexed until the thigh was vertical; the opposite leg was held in the fully extended position. The foot of the leg being tested was kept relaxed, whereas the knee was actively straightened until the point when the thigh begins to move from the vertical position. The angle between the thigh and shank at this point was recorded, where a straight leg was considered as 180°. The measurement of knee extension was made with the hip in the neutral position and the knee maximally extended, a straight knee noted as 0°, and an extension defect in negative figures (−). The research physiotherapist made all measurements. Goniometric measurement is a valid and reliable method of measuring ROM19 and can be measured in a reproducible manner in children with multiple disabilities.20 Data on passive ROM were graded according to the “traffic light signals” in the national surveillance program,17 where the green zone indicates sufficient ROM, the yellow zone means slightly impaired ROM, and the red zone is impaired ROM.

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Muscle Tone

Muscle tone in the hamstring muscles was assessed using the Modified Ashworth Rating Scale (MAS)21 with the child in a supine position and the hip flexed to 90°, while a quick stretch to the hamstrings was applied. The MAS is tested for validity and reliability.22

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Gross Motor Function

Gross motor function was assessed with the Gross Motor Function Measure (GMFM).23 This is a clinical tool designed to evaluate change in gross motor function in children with CP. The GMFM-88 version was used, including all 5 dimensions.

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Diary

A diary was used in which the child, parent, school staff, or a personal assistant reported for how long the knee orthoses were used each day. The diary was also used for comments on the intervention.

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Intervention

All children had knee orthoses made for both legs, fabricated by the child's regular certified orthotist (Figure 1). The orthoses were made from polypropylene and secured by straps and were made to the maximum allowed range of knee extension. The intervention lasted 8 weeks. Participants were required to use the orthoses at least 30 minutes for a minimum of 5 days a week.

Fig. 1

Fig. 1

The child's position was sitting, well supported, with the hips up to 90° of flexion, the knees extended, and the legs slightly in abduction.

The research physiotherapist applied the knee orthoses for the first time to determine a position for the intervention that could be maintained for at least 30 minutes. A photograph was taken of the child in that position so that the intervention position could be repeated. The parent, school staff, a personal assistant, or the child herself or himself performed the intervention.

All children continued with their usual physical therapy, with no changes during the intervention period.

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Statistical Analysis

To analyze ROM from baseline to the intervention phase for each leg, a visual analysis was used with the Two Standard Deviation Band Method (2SD method).24 The 2SD method is based on the computation of the standard deviation (SD) for the baseline data. Once the SD is computed, bands are drawn on the graphs that contain scores within 2 SD from the mean. If at least 2 consecutive data points in the intervention phase fall outside the 2SD band, the change is considered as statistically significant. This procedure has the advantage of being sensitive to changes in variability across the phases of a single-subject design.

The data were also tested on a group level. As the sample size was small and the data were not normally distributed, this was performed with a nonparametric paired analysis using the Wilcoxon signed rank test with the software SPSS for Windows (version 22). The mean of measurement from baseline data was compared with the mean of the last 4 measurements in the intervention phase. Testing was made on the right and left legs separately. A P value of less than .05 was considered as statistically significant.

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RESULTS

Thirteen children were asked to participate in the study and 10 agreed. All completed the study. The recruited children were aged 5.7 to 14.6 years. The mean age was 10.8 years (SD = 2.97). There were 4 girls and 6 boys included in the study; 4 were ambulators without aids (Gross Motor Function Classification System [GMFCS] levels I and II), and 4 were ambulators with devices (GMFCS levels III and IV). Two were nonambulators, classified as GMFCS level V. Four children had bilateral CP, 4 had a dyskinetic type of CP, and 2 had an unspecified type. The characteristics of the sample are summarized in Table 1. In total, 20 legs were treated.

TABLE 1

TABLE 1

The goal for the intervention was set to a minimum of 30 minutes per day, 5 days per week during the intervention period of 8 weeks, in total 40 sessions of 20 hours. Participants compliance with the orthoses was high; they completed on average 40.9 sessions (range, 30-51) (Table 2). Some of the children used the knee orthoses for more than 30 minutes each time, and some of them 6 or 7 days a week instead of 5.

TABLE 2

TABLE 2

There were no changes in their usual physiotherapy program during the intervention period.

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Range of Motion

During baseline measurements, the passive ROM measurements for the hamstrings and knee extension for both right and left legs were stable (Table 2). Visual inspection showed that all children had an increase in passive ROM in the hamstring muscles after 8 weeks.

According to the national surveillance program, 10 legs were within the yellow and red zones and 10 in the green zone (of which 7 were very close to critical values) before the intervention. After the intervention, there were only 2 legs still in the yellow zone and 18 legs were in the green zone.

The data from each leg were analyzed with the 2SD method. At least 2 consecutive data points in the intervention phase fell outside the “2SD band” in all hamstring muscles (Figure 2). All comparisons between baseline and intervention within subject are significant in all 20 hamstring muscles. In knee extension, 12 of 14 results were significant using the 2SD method. In 6 legs, there were no knee extension contractures at baseline.

Fig. 2

Fig. 2

We observed that major parts of the increase were seen after 4 weeks of intervention (Figure 3), and changes in passive ROM were greater in children with less severe involvement at GMFCS levels I and II. The child who used the orthoses most frequently had the best results in passive ROM in the hamstrings; however, there were too few participants for statistical analysis.

Fig. 3

Fig. 3

An analysis with the Wilcoxon signed rank test confirmed the individual results. There were significant increases in ROM in the hamstring muscles compared with baseline (P = .005 in both right and left sides), as well as in knee extension (right: P = .03; left: P = .02).

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Muscle Tone

All children had increased muscle tone in the hamstring muscles in both legs at baseline. After the intervention, 4 children had decreased spasticity in 5 legs. The difference was statistically significant for both right and left sides (P = .005).

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Gross Motor Function

Two children did not participate in the GMFM test at baseline and could not be evaluated: in one due to lack of ability to follow instructions, and in one due to illness at planned time for test. Two children had small improvements in items for crawling and jumping on 1 leg, but the changes were not statistically significant.

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Diaries

Diaries were controlled for comments. During the first week of the intervention, 1 child reported a swollen knee and 1 child had “cramp” at 1 occasion. No other complications or negative comments were recorded. Parents and staff at school reported differences in activities of daily life, for example, “easier to position in the wheelchair” and “that it was easier to sit on the floor with the other children.” One child described that she was more relaxed with the orthoses and chose to use them almost 7 days a week. Five parents planned that their child would continue with the orthoses after the intervention.

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DISCUSSION

Although orthoses are frequently used to maintain length of the hamstrings and are believed to contribute to improvement in passive ROM, few studies examined the effect of knee orthoses.

The present study supports that it is possible to affect length of the hamstrings and knee contractures using prolonged stretching. This supports the findings of Gibson et al,13 who found that 1 hour of standing in a standing frame, 5 days a week, led to a significant improvement in length of the hamstrings and that length of the hamstrings decreased again during periods without daily use of the standing frame. The group in our study was heterogeneous regarding the severity of motor function and represented all 5 GMFCS levels. The 2 children with the most severe involvement (GMFCS level V), who had the smallest increase in passive ROM, were also the children with the most severe knee contractures at baseline. The large difference in length of the hamstrings from baseline to intervention suggests that the intervention method was successful.

Statistically significance may not always mean that the difference is clinically significant. However, all of the participants were considered to have contractures, raising an alert in the traffic light system in the national surveillance program,17 values that indicate a risk of affecting motor function and sitting position. After the intervention, only 2 legs were still in the yellow zone, implying that the intervention was clinically meaningful.

Frequency and duration of the intervention need further examination, but our sample size was too small for statistical analysis. The child who used the orthoses most frequently had the best results in the passive ROM in the hamstrings, and the 3 children who used the orthoses in the fewest sessions achieved the poorest results. Most of the children, however, used the orthoses at least 30 minutes per day, 5 days a week, which suggests that this was a sufficient time to achieve results. The major increases were reached within 4 weeks of intervention, suggesting that the intervention period could have been shorter than 8 weeks. It would also be interesting to know whether a lower frequency of use of the orthoses would have been sufficient to maintain the results.

We found no effect on gross motor function. This may have several explanations including that the sample was small; there were only 8 children who fulfilled the GMFM tests, which led to lower statistical power. There is little published evidence regarding the relation between joint mobility and motor function, and no strong relationship has yet been demonstrated.25 However, in our clinical experience, sufficient extensibility of the hamstrings is necessary for a good posture when sitting for a longer period. Short hamstring muscles may pull the pelvis into a backward tilt, forcing the head and shoulders to compensate with protraction, which is not an optimal position for fine motor activities. This affects daily life activities, such as dressing and school activities. Sitting time increases from school age onward. The GMFM outcome measure may not be sensitive enough to assess the sitting function, where items on sitting include the ability to move in and out of different sitting positions and hold a position for a maximum of 10 seconds. There is a lack of instruments that evaluate how a sitting position affects arm and hand functions.

The authors found a small but significant decrease in spasticity. This improvement may have contributed to the experience of more relaxed sitting, which was commented upon in the diaries.

Compliance in the study was good. The regimen with daily use of orthoses and making daily notes in the diary might have made it easier to follow the intervention. The fact that the physiotherapist came weekly to perform the measurements and to read and discuss the notes in the diary might have been a motivational factor contributing to the high compliance.

The study has limitations. It is a small study with only 10 children, and we have only explored the short-term use of orthoses. The long-term effects of this intervention are not yet known.

Children with CP are a heterogeneous group and often receive a variety of interventions, which makes it difficult to compare effects of interventions. In this study, the regular therapy for each child did not change during the period. Hamstring stretch with knee orthoses was added and thus changes can be attributed to this intervention.

The Ashworth scale is a widely used clinical measure of spasticity, but there is discussion of its validity and precision. In the present study, the same physiotherapist made all measurements, which removes the measurement error that can occur between testers but not the fact that the physiotherapist was not blinded. Despite the best intentions to be impartial, it is possible that this may have biased the results. While it would have been preferable to have a blinded assessor carry out the measurements, this would have involved using an extra physiotherapist, which was beyond the study resources. Blinding participants was impossible, as is frequently the case in studies evaluating therapeutic interventions.

There is a need for more research on the use of orthoses, particularly the use of orthoses at rest, to guide both parents and therapists. This study is a pilot study of a method that can be implemented in a daily routine. Future studies should include more participants and a comparison group to be able to generalize results. As contractures develop over years, there is a need for a longer follow-up period. There is also a need of more knowledge about how these interventions affect important aspects of children's and families' activities and daily lives. The lack of evidence from well-controlled trials is a problem in clinical practice, but it should not deprive children of therapeutic options such as orthoses. Evidence-based practice includes integrating both individual clinical expertise and research.

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CONCLUSION

This study supported that 8-week use of orthoses for 30 minutes, 5 days per week, significantly improved passive ROM in the hamstring muscles in 10 children with spastic CP. However, as the number of children was small, further studies are needed to confirm the results.

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Keywords:

cerebral palsy; cerebral palsy/rehabilitation; muscle spasticity/rehabilitation; orthoses; physical therapy techniques/method

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