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Does the use of a kneeblock influence hip deformity, sitting ability and pain in children with bilateral cerebral palsy? 

Aim and background of project

Kneeblocks are used by some clinicians and some services across the UK and not at all by others. Opinions on the potential benefits or risks are strongly divided. However, there is little scientific evidence currently available to inform this ongoing debate.

A randomised controlled trial was, therefore, proposed. The objective of the study was to determine whether using a kneeblock and sacral pad as part of seating system influenced outcomes in children with bilateral cerebral palsy who cannot walk. The outcomes of specific interest were hip migration taken from radiographs, pain, hip range and sitting ability.

Cerebral palsy is a disorder of posture and movement, which is persistent and caused by a non-progressive brain lesion, arising before or around birth, during the time of rapid brain development. Although the underlying lesion is static, the resultant disability and postural deformity can deteriorate significantly and rapidly. Spastic quadriplegia now accounts for approximately one third of all children with cerebral palsy. The proportion of children with cerebral palsy in Oxfordshire who were still not walking by the age of five years increased from 28.4% in 1984 to 45.7% in 1992. It is this non-ambulant spastic quadriplegic group that seem to be particularly at risk from the development of contractures, windswept deformity and hip dislocation.

When specifically looking for windswept hip deformity, the prevalence was reported to be as high as 52% or 59%. In a benchmark study in 1997 Scrutton & Baird (1997) found that the prevalence of hip subluxation/dislocation in children with bilateral cerebral palsy was 31% of hips in 40% of children. They also reported that the prevalence increased to 58% when looking specifically at children not walking by 5 years of age.

About one third to one half of the children with dislocated hips have pain and the severity of pain is thought to be related to the degree of subluxation, with dislocation producing the most pain. It has been reported all hips subluxed greater than 80º are painful and that in a study of 34 people with cerebral palsy, 18 who underwent hip surgery did so primarily for the purpose of relieving pain. Unilateral or bilateral hip dislocation in children and adults with cerebral palsy is likely to cause difficulty in achieving sitting balance and maintaining a good sitting position. Carrying tasks such as manipulation, visual tracking, feeding and social interaction are also likely to be more difficult as a result of the postural instability.

Pountney (2002) carried out a retrospective analysis of 60 children with bilateral CP. She compared hip migration for three groups of children who had undergone different amounts of postural management. The results suggested that hip migration reduced when using several types of postural management, including appropriate wheelchair seating and night lying equipment (“24 hour postural management”). Although the outcome from this study was helpful, it was not clear which parts of the overall package of postural management were effective. Kneeblocks were used as part of the overall approach to postural management, however it was not possible to say from this research whether the use of kneeblocks specifically had any effect.

The knee block is thought to reduce the chance of subluxation and dislocation of one or both hips and thus, to improve comfort. The kneeblock is also thought to help to achieve stability of the pelvis with the aim of improving trunk balance and upper limb function. However, there is little scientific evidence currently available to support, or question, the use of kneeblocks to achieve the above outcomes.

MacDonald suggested that the pelvis was less posteriorly tilted in the sagittal plane when a force was applied through a kneeblock on a seating system. Apart from this study, there is very little scientific evidence available relating to the use of kneeblocks. Opinion and practice among clinicians is very much divided, with strong views existing on both sides. Some believe that if the kneeblock is used appropriately it can offer significant benefits, where as others believe it presents the user with risks. This was debated fiercely at The Annual Scientific Conference of the Posture and Mobility Group For England and Wales (Nottingham, 2004). There was, and still is, an urgent need for evidence to inform this debate and for decision- making.

Methodology

The study was designed as a randomised controlled trial. The plan was to conduct it over a five-year period.

Participants were young people with bilateral cerebral palsy who were between 2 and 13 years of age, level IV or V on the Gross Motor Function Classification System for cerebral palsy and with sufficient range of movement at the hips to allow the use of a kneeblock. The participants were randomly assigned to a modular seat either: (a) with a kneeblock and sacral pad; or (b) without a kneeblock and sacral pad. Measurements were to be made annually for each participant over three years. A sample size calculation identified that 100 participants would be required to reliably answer the primary research question. Recruitment took place initially in Oxfordshire and various districts of Yorkshire. Services in other areas were subsequently approached. R&D approval for each of the new areas was sought and recruitment started in some of these areas.

Inclusion criteria

  • Age 2 to 13 years at the start of the trial
  • Bilateral cerebral palsy
  • Group 4 or 5 on the Gross Motor Function Classification system for cerebral palsy (Palisano et al 1997)
  • Sufficient range of motion at hips to allow the kneeblock to be fitted without causing additional rotation of the pelvis
  • Need for supportive seating accepted by family and clinicians
  • Expected to use seat for at least two hours per day.

 Sample Size Calculation

 For this specific study population, the mean hip migration percentage at three years of age was estimated at 18% and the rate of deterioration as 6% per annum, based on work published by Scrutton et al (2001). The standard deviation was estimated as 12% using data from a recent study by Pountney (2002). If a 50% mean difference in migration percentage was to be detected between the intervention and control group, for a power of 90% and significance level of 5%, a total sample size of 76 was required (i.e. 38 in each of the intervention and control groups). However because of the potential dropout rate in this study, a target of 100 participants was set.

Recruitment process

Medical consultants, community physiotherapists, community occupational therapists and wheelchair service staff in the study regions were asked to identify suitable children, based on the inclusion and exclusion criteria detailed.

An invitation letter and information sheet was then provided by the identifying healthcare worker. Families were asked to reply to the researchers, indicating if they were, or were not, interested in taking part in the study. Reply slips, along with a stamped, addressed envelope and contact telephone details for the researchers, were provided.

The researchers made contact with the families who had expressed an interest in participating in the study and an appointment with the child and parents was arranged. At this appointment the research study was discussed, any questions answered, and when appropriate, informed written consent obtained. Where potential applicants were identified whose first language was not English, the NHS translation and interpretation services were used. Initially, recruitment was focused on users of health services in Oxfordshire and various health districts of Yorkshire. Later in the study, the geographical area of recruitment was significantly expanded.

Intervention

Both groups used adjustable modular wheelchair seating. The orthogonal modular seating included: ramped seat base, backrest, lateral pelvic and thoracic supports, pelvic belt and foot supports. A head-rest, chest harness and tray were optional.

The intervention group used an appropriately adjusted kneeblock and sacral pad, whereas the control group used the seating without a kneeblock and sacral pad.

Participants and their families were free to choose between these two seating systems: (a) the Active Design CAPS 2 seat; and (b) the RMS Gill 3 seat. It was considered important to offer potential recruits a choice of seats. The two seats were different aesthetically but were similar in terms of the biomechanical application of forces to the body (in particular when considering the kneeblock and sacral pad).

The detailed specification of the required seat was determined by the researcher, who then liaised with the local wheelchair service to request they provided an appropriate wheeled base. When appropriate, the local social or education services were also approached and asked if they would provide a space-saving castor base for use at home or school, respectively. Care was taken to ensure that the seat dimensions, configuration, options and accessories were specified accurately and appropriately. The seating was then delivered to the participant and carefully adjusted to ensure biomechanical forces were applied appropriately. Family and staff at school were shown how to use the seating and how to check that the seat was still adjusted appropriately. The participants’ families were contacted at least monthly to check that all was well. The participants were also visited regularly to check and adjust the seat and resolve any issues as they arose. Replacement components and whole seats were ordered, as necessary. The use of the seating was monitored over the three-year period over which each participant was taking part in the study.

Outcome measures

1. Hip migration

Hip migration percentage was identified as the best measure of hip integrity (Scrutton et al 2001). It is based on an antero-posterior radiograph of the head of femur and acetabulum, and records the percentage of the femoral head, which lies beyond the lateral border or the acetabulum.

Current guidelines for hip surveillance for the population included in this study recommend radiographic assessments are carried out at least. Therefore, the children taking part in the study were not being asked to undergo more radiographs (and therefore, more exposure to radiation) than they would, or should be normally. If an annual review radiograph had been taken with three months of the initial time that it was needed for the baseline measurement in the study, then the existing radiograph was used. If not, a radiograph was requested. Subsequent review radiographs were requested annually after the baseline radiograph. Guidelines on standardised positioning for the radiographs, in order to optimise the accuracy of the hip migration percentage measure, were provided to radiography departments and to the families to take along to radiography appointments. All hip migration percentages were carried out by a trained therapist who was blinded to whether the participant was allocated to the intervention or control group. Anonymised radiographs were posted (or sent electronically) to this therapist, who was based away from both research sites.

2. Secondary outcomes

The range of ab/adduction, internal/external rotation and flexion/extension was measured with the subject in supine, using simple mechanical goniometers and standard clinic procedures. Sitting ability was assessed using the Chailey scale. This is a standardised and validated test designed specifically for the population with neuromotor deficits involved in the study.

The paediatric pain profile was used. This is a 20 item behaviour-rating scale to assess pain in children with severe neurological impairment. QUEST 2.0 was also used. This is a 12-item questionnaire-based outcome measurement tool to assess user satisfaction with assistive technology interventions. Although not intended to be used in the formal comparison between intervention and control group, it was thought that the Quest 2.0 would provide a useful source of more qualitative information that would shed light on the experience of the participant and their family when using this type of equipment. All the above outcome measures were carried out at the baseline assessment and subsequent annual reviews.

Ethical approval

The study was reviewed and approved by both the School of Health & Social Studies (Oxford Brookes University), Research Ethics Committee and also the Leeds (East) Research Ethics Committee of the NHS National Research Ethics Service [ref 05/Q1206/8]. Multi-centre NHS ethical approval was given, although it was also necessary to seek approval from local R&D Departments of all NHS care organisations.

Discussion and further work

Recruitment took place initially in Oxfordshire and various districts of Yorkshire. Services in other areas were subsequently approached. R&D approval for each of the new areas was sought and recruitment started in some of these areas. However, after 20 months only 25 participants had been recruited to the study. In July 2008 it became clear that it would not be possible to recruit the required number of participants within the constraints of the resources/time allocated for the study. Therefore, a decision was reluctantly made to end the study early.

The relevance of this study, had it been completed, was that it would have contributed to the development of a more evidence-based approach to the use of kneeblocks, thus allowing children, families and healthcare professionals to make more informed decisions about their use. The research team have learned valuable lessons about planning and staffing a large multi-centre trial in the rehabilitation field from the experience of attempting this study. In retrospect, it can be seen that the study should have been designed from the outset with participants being recruited from more services, over a larger geographical area. This, in turn, would have had implications in terms of the way the study was staffed and managed.

The biggest surprise, however, was the attitude of some therapists and other healthcare professionals to this type of research. There seemed to be no disagreement with the justification for the study, i.e. the fact that evidence was scarce or non-existent and that research was desperately needed to inform practice and decision-making. Despite the lack of evidence, there was reluctance among some (but not all) to allow their clients to be randomised one way or the other. Some thought that randomisation was actually unethical. However, the research team agreed with the ethics committee, arguing that continuing the situation where decisions are made about using kneeblocks or not, without evidence is more of an ethical concern.

Because this study focused on a particularly controversial topic, where very strong views and opinions exist, it seemed to make the anxiety about randomisation more pronounced. However, the fact it was a controversial topic and very different views and practices exist, surely makes research on this question even more important. It is suspected that randomisation would be less controversial in other fields of healthcare where there is generally more of an acceptance of the role of research. Work clearly needs to be done to challenge the views of some therapists and other healthcare professionals in this particular field, on research in general and specifically, the acceptability and feasibility of carrying out randomised controlled trials.

In conclusion, the research question that this study was based upon still needs answering. A study to address this research question needs to be completed and the sooner this is done, the better. Based on the experience from the study described in this report, it is suggested that rather than relying on a small number of centrally- based researchers, an alternative approach would be to train and support large networks of therapists working from within their own local services.

This information is not meant to replace the advice of any physician or qualified health professional. The information provided by Cerebra is for information purposes only and is not a substitute for medical advice or treatment for any medical condition. You should promptly seek professional medical assistance if you have concerns regarding any health issue.

Page last updated: 21/12/2011 15:56 
 
 
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