Background
Cerebral Palsy (CP) is classified as a group of postural and motor disorders caused by a non-progressive lesion to the developing brain, aquired before the age of two [
1,
2]. Affecting approximately 2.11 per 1000 live births worldwide and slightly less in western countries (e.g. Sweden with 1.96 per 1000 live births) [
3], CP is a prevalent condition seen in the paediatric healthcare setting [
4]. The impact of CP on functional capacity varies greatly as does the level of disruption to the developing brain [
5]. Due to its non-progressive nature, a focus of rehabilitation by physiotherapists is managing associated primary and secondary complications, such as spasticity and contracture, which are often not present at the time of the initial injury to the brain [
6]. This focus is clinically reasoned to be an initial step towards improved mobility, so that the focus of rehabilitation can progress towards more functional activity and participation goals, which are thought to be more meaningful activities to individuals with CP for their daily living [
7] .
Among the different types of CP, spastic CP is the most common form consisting of approximately 85.8% of diagnoses [
8]. Spasticity of a muscle is defined as a velocity-dependent resistance of a muscle to stretch [
9] impacting the range of motion around a particular joint [
10]. Without appropriate management, spasticity may contribute to the onset of contractures of the muscles, ligaments and tendons [
11,
12], affecting loading biomechanics and causing major functional limitations [
13]. For example, contracture of the gastrocnemius-soleus complex can cause equinus positioning of the foot, which adversely affects standing balance and increases energy expenditure during walking [
14,
15]. Interventions focused on improving posturing of the lower limb would likely enhance gait kinematics and improve walking distance [
14]. Many studies have identified the amplified functional impact that contractures, specifically contractures of the lower limb, have on ambulation and a child’s ability to complete functional everyday tasks [
16,
17]. There is a clear need to identity the most appropriate and effective intervention strategies to minimize negative effects and maximize functional outcomes.
Current clinical management of spasticity and contracture in the lower limb includes conservative approaches such as the use of physiotherapy, orthoses, casting and splinting [
18]. Other commonly used invasive strategies for spasticity and contracture management include neurotoxin injections such as botulinum toxin A (BTX-A) and intrathecal baclofen, as well as surgery such as selective dorsal rhizotomy (SDR) and various corrective orthopaedic operations [
11,
17] including tendon lengthening procedures and single-event multilevel surgeries (SEMLS) [
19,
20]. Previous studies have supported the efficacy of interventions including BTX-A, diazepam and SDR for the management of spasticity [
17,
21‐
23]. However, some previous research findings suggest that surgery for children with spasticity, if performed at a young age, can yield undesirable and sometimes unpredictable outcomes such as recurrent equinus, infection and over-lengthening of muscle tendon units [
22‐
24]. As a result, non-surgical interventions have been suggested clinically as temporising measures until the child is more musculo-skeletally developed [
23].
In the research literature, serial casting is commonly referred to as the application of two or more successive fibreglass or plaster casts to a particular joint with efforts to increase passive range of motion (PROM) around a joint by maintaining prolonged passive stretch in the submaximal or maximal range [
21,
25‐
27] which allows more opportunity for active ROM (AROM). Submaximal refers to the point between initial resistance to passive stretch and the point at which no further stretch is possible and is determined by the clinician as well as patient tolerance [
28,
29].
A recent review of systematic reviews conducted by Novak and colleagues [
17] summarized the evidence of various interventions for children with CP. Evidence was found to support the use of lower limb casting to alter body structures, however, only low-quality evidence was reported to have a positive effect on improving activity limitations as per the International Classification of Functioning, Disability and Health (ICF) model [
30]. In relation to the lower limbs, increased physical activity was the most common recommendation for targeting a child’s ability to complete activities (e.g. walking) [
17].
Several authors from studies cited in two previous systematic reviews [
17,
25] recommended serial casting be used to improve PROM at the ankle to enhance functional outcomes in children with CP. However, because serial casting is commonly used in combination with BTX-A injections [
21,
31] and other therapies [
19], the isolated effects of serial casting on the lower limb and in particular short-leg walking casts have not yet been clearly identified in the research literature [
32], despite it being a common therapeutic intervention in the management of children with CP [
21]. In 2007, Blackmore and colleagues published a systematic review reporting on limited evidence, suggesting that serial casting is more effective in the management of secondary complications of CP than no serial casting [
21]. This previously published evidence regarding the effects of serial casting alone to influence lower limb function warrants further investigation with recent additions to the empirical literature. Additionally, Blackmore et al. acknowledge that many studies included in their review had insufficient sample sizes, lacked randomization and lacked blinding, making it difficult to identify the true effects of the interventions [
21]. For this reason, it is important to ensure that conclusions regarding the effect of serial casting on the lower limb are based on studies with sound methodological quality. More recently two systematic reviews [
32,
33] explored the empirical literature to determine the efficacy of using adjunct therapies to improve outcomes after BTX-A injections in children with CP. Whilst both systematic reviews are valuable contributions to the research literature, the aims and findings of these reviews are impacted by the contribution of BTX-A and do not set out to explore the effects of serial casting independent of pharmacological interventions such as BTX-A.
Despite the conclusions of previously published systematic reviews, it is still unclear as to whether serial casting is effective for improving lower limb function (including the body function and structure and activity level functions such as gait and gross motor proficiency) in children with CP. This uncertainty is attributed to a wide range of study designs, casting protocols, and combinations of additional therapies documented in the current literature, making it difficult to isolate and determine the efficacy of serial casting as an intervention [
17,
25] independent of pharmacological therapies. Considering recent contributions to the empirical literature regarding the potentially damaging effects of BTX-A to gait in children with CP [
34], the findings from this systematic review are warranted to assist clinicians, parents and clients in shared decision-making processes. As such, the purpose of this systematic review was to critically appraise and synthesize the empirical literature regarding the effects of serial casting, compared to serial casting with pharmacological intervention, on the different variables influencing function of the lower limbs, in children with CP. In synthesizing the findings from moderate to high quality studies, the authors of this review aimed to:
1.
Determine the effects of serial casting as a therapeutic intervention in isolation or in combination with other therapies (which may include pharmacological intervention) on lower limb dysfunction in children with CP.
2.
Determine the effects of serial casting at different points in time post cast removal.
3.
Determine if the addition of pharmacological intervention enhanced the effects of serial casting on lower limb function.
By expanding on previous reviews as well as including findings of recently published studies, this review may assist clinicians and families with clinical decision-making regarding the selection of serial casting as a possible intervention modality. For this review, passive range of motion (PROM) of the ankle is considered the critical outcome of interest, however, other important outcomes impacting lower limb function will be investigated, as will adverse events relating to serial casting protocols.
Discussion
The overall objective of this systematic review was to identify the efficacy of serial casting as an intervention in the management of lower limb dysfunction in children with Cerebral Palsy. Other systematic reviews have addressed the utility of serial casting as an adjunct to pharmacological intervention [
32,
33] or are now considered to be out of date [
17,
21,
25]. No recent publications have summarized findings solely according to higher methodological quality studies to determine the effect of serial casting on lower limb function, nor have recent publications provided a meta-analysis of findings relevant to the study aims to allow more robust conclusions. The results of this systematic review with meta-analyses suggest that serial casting (independent of BTX-A) can have significant desirable effects on i) increasing ankle DF PROM in the immediate (IP) to mid-term (MT); ii) reducing hypertonicity in the short-term (ST) and; iii) improving functional gait in the mid-term (MT). Furthermore, the findings of this review indicate that the effects of serial casting on ankle DF PROM are further and significantly enhanced by the combination of BTX-A, however the clinical significance of the magnitude of this effect remains unclear. These findings support the use of serial casting in clinical practice to manage impairments at the body function and structure level to improve lower limb activities such as gait.
Relevant to the first aim, the strongest findings were in the immediate (IP) and short-term (ST) periods post casting, when the knee position was unspecified (KPU) for DF PROM measurement, which made it difficult to differentiate the most implicated muscles involved in the overall effect. However, serial casting appeared to have the strongest effect on the soleus muscles of the triceps-surae three to six months after serial casting. This may be the result of the gastrocnemius muscles shortening quicker than the soleus muscles after earlier gains from serial casting. However, in order to truly understand what components of casting are causing the most effective outcomes, it is recommended that future studies include more detailed reporting of their casting protocols (i.e. casting duration and position, subject positioning, weight bearing status, casting material, as well as adjunct therapy before, during and after serial casting) and measurement protocols, to enable better identification of possible contributors for the effects of serial casting. For example, if a below-knee cast is applied, with the intent to lengthen the gastrocnemius, one may clinically reason that the footplate of the cast needs to end distal to the first toe, with the footplate of the cast having a flat sole, without the addition of an inserted rocker, and that a regular exercise program utilising full knee extension in standing and walking activities should be prescribed. If the details of the casting protocol were consistently described, it may be possible for future reviews to identify which components are having the most effect on the studied outcomes.
When used in clinical practice, the main aim of serial casting is to increase PROM around the ankle to eventually achieve adequate AROM at the ankle to reach heel strike at first foot contact, to consequently improve functional gait parameters and other age-specific functional outcomes. Data synthesis (see Tables
3 and
4), identified that serial casting overall did not have a significant effect on walking velocity or stride length. However, it is important to note that for walking velocity, only two studies reported significant effects, one of which [
52] claimed that that serial casting had a significant undesirable effect on walking velocity and stride length immediately post-cast removal (one week after final cast removal). However, statistical results were not reported for stride length and this study used serial casting after BTX-A injections. This undesirable effect is most likely attributed to the weakening impact of BTX-A and the negative implications that prolonged immobilization has on muscular strength, and this hypothesis is supported by the increased adverse effects for children when serial casting and BTX-A were combined. This negative effect has been described previously in the empirical literature [
61], where ankle plantar-flexion torque, fatigue resistance and functional recovery following casting for ankle fracture were examined. Reduced ability to generate plantar-flexor muscle force has direct implications during the late stages of stance phase, which can ultimately influence stride length and gait velocity [
62]. This undesirable effect indicates a need for intermittent serial casting with lower limb strengthening incorporated in-between cast applications, as opposed to continuous casts over prolonged periods. The recommendations by Novak and colleagues in 2013 [
17], regarding lower limb strength training and electrical muscle stimulation, appear critical for enhancing a child’s strength and therefore function, post- and perhaps during serial casting episodes, especially when using prolonged serial casting protocols. Most studies with intermittent casting protocols were excluded from this systematic review as they failed to meet our pre-determined definition of serial casting. Results pertaining to muscle strength post-casting were not reported in this review as there were not sufficient studies investigating this outcome in the included literature. Further investigation into the effects of combining serial casting with brief (e.g. 1–2 days) non-casting periods of age-appropriate strengthening activities is therefore warranted.
Another desirable effect of serial casting identified in this review was the reduced influence of hypertonicity on muscles around the ankle joint, in the short-term (ST) post-cast removal. The authors of this review feel that these benefits may have translated into the improvement in functional gait described in some studies [
22,
53], with improved ankle DF PROM allowing for improved clearance of the foot in the mid-swing phase of a limb implicated with hypertonicity. Important to addressing the aims of this study, functional gait improvements (using objective standardised measures) were observed in studies that used serial casting without pharmacological intervention (see Table
4) although meta-analyses did not demonstrate a carry-over effect with gross motor skills as significant changes in gross motor function measure scores were not observed. An improved ability to reach heel strike may have accounted for improved balance, which is reflected in the improved functional gait outcomes reported in this review. The decrease in hypertonicity in the lower limb post-casting reported in studies assessing hypertonicity using the MAS [
11,
22,
31,
48,
52,
58] may also have positively impacted functional gait for similar reasons. Whilst the MAS is a commonly used measure in clinical practice, future research could use more objective measures (e.g. electromyography) to quantify the responses of serial casting on hypertonicity levels, which may allow for more definite assessments of the relationship between decreased levels of hypertonicity and improved gait and / or gross motor outcomes.
In addressing the second aim of this review; the effects of serial casting longitudinally, the authors identified that there were no fair or good quality studies investigating the long-term effects of serial casting (i.e. greater than six months) independent of pharmacological intervention, on lower limb function for ankle DF PROM, hypertonicity (MAS), spasticity (MTS), gait (OGS) or gross motor function (GMFM). It is therefore recommended that future longitudinal studies are conducted to determine the efficacy and sustainability of serial casting as an intervention for long-term management of lower limb dysfunction in children with CP. The findings from future longitudinal studies, particularly if compared to long-term effects of additional pharmacological interventions, would further assist parents/carers in their decision-making regarding preferred methods of intervention. These options should then be discussed with children and their carers using shared decision-making models for treatment planning [
63].
The findings related to the third aim of this review suggest that the addition of pharmacological intervention to serial casting results in slightly yet significantly better ankle DF PROM; however, these findings should be interpreted with caution. An additional two-to-three degrees of ankle DF PROM may translate to be functionally beneficial if the ankle DF range of an individual is within a few (two to three) degrees of achieving neutral ankle DF. However, this may not be functionally beneficial if the individual has either i) already achieved neutral ankle DF, or, ii) is substantially greater than three degrees away from achieving neutral ankle DF from an originally plantarflexed position. During human gait, critical foot clearance is influenced by slight movements at the ankle joint. A study undertaken by Moosabhoy and colleagues in 2006 [
64], suggested that the point of critical toe clearance occurs when the ankle is slightly dorsiflexed (at approximately one degree past neutral). Therefore, if the addition of two-to-three degrees ankle DF from the pharmacological intervention (i.e. BTX-A) achieves range through the point of critical toe clearance, then it is likely to be of clinical value above and beyond serial casting alone. Importantly, our sensitivity analysis showed that the difference in DF PROM between serial casting and serial casting with pharmacological intervention (which in all cases was BTX-A) became non-significant when one study [
28] that used alternative measurement options was removed from the meta-analysis. This suggests that the findings rest on limited data and further high quality randomized controlled trials exploring the differences between serial casting and serial casting with BTX-A or other pharmacological interventions are needed. Further, only one of the three studies clearly identified the knee position as being extended during measurement of ankle PROM and whilst the other two studies implied that the knee was extended, implicating the effect in the gastrocnemius muscles, there was a lack of clarity from authors of the included studies for reporting the measurement protocols. In view of our findings, it is important for clinicians to take into consideration that certain pharmacological interventions such as BTX-A are neurotoxins and whilst medically controlled they are considered safe for use with children, however, are generally more invasive with potentially higher risks [
65]. Consequently, it is imperative that clinical reasoning and specific goal-setting related to lower limb function is incorporated in the family-centered decision-making process prior to recommending the addition of BTX-A to serial casting, on the basis that it is likely to result in only slightly better ankle DF PROM (see Fig.
7) with potentially more adverse effects.
In undertaking this systematic review, the authors identified several limitations in the published empirical literature. Many of the articles included had poor methodological quality, which was commonly attributed to a lack of detailed reporting of either the methods and/or results of the study. For example, many studies failed to report actual probability values, did not use appropriate statistics, or did not report statistical tools used. Several studies used the ANOVA statistical method of analysis without reporting a post-hoc analysis, preventing the identification of the point of significant difference from baseline to each post-treatment measure. This lack of detailed reporting also limited the ability to include such studies in the meta-analyses for this systematic review. Consequently, the authors of the present review needed to use estimation calculations or to exclude data from meta-analyses, which limited the ability to draw firm conclusions regarding the aims of this review and may have contributed to the substantial heterogeneity observed in many of the meta-analyses. In future research, it is recommended that authors report all statistics thoroughly, particularly mean values with standard deviations for transparency of findings and or publish their complete set of de-identified data. This will enable more sound analyses to be made in future systematic reviews and consequently firmer conclusions can be made.
The inconsistency of the data from the variety of assessment methods and outcome measures used, made it difficult to synthesize and quantify the magnitude of the reported serial casting effects. Additionally, the method of cast application was varied and on many occasions was not reported at all, making it challenging to analyze and quantify the potential impact of different serial casting protocols on lower limb function. Factors such as the duration of serial casting, the goal of serial casting, materials utilized, and different combinations of adjunct therapy varied immensely across the included studies and were also likely contributors to the large degree of heterogeneity, commonly prohibiting pooled effect estimates being calculated. The authors of this review recommend that future research relevant to this topic consider using casting protocols that are already prevalent in the literature or report their methodology in a detailed manner which would permit replication of methods, to allow the effects of serial casting to be thoroughly explored in future systematic reviews. The authors of this review acknowledge that to do this, journal publishers need to allow for extended word counts in presenting the methods of studies undertaken. Furthermore, this review revealed large degrees of heterogeneity for a number of analyses, and this was mostly related to the inconsistency of casting protocols, age populations and GMFCS classifications. Blackmore and colleagues in 2007 [
21], reported a similar issue, stating that studies in their review had small sample sizes and lacked randomization and blinding, making it challenging to identify the true effects of serial casting as an intervention. To reduce the impact of these limitations, future studies should report detailed assessment and intervention protocols and procedures. Additionally, randomized controlled trials contrasting the effects of serial casting versus serial casting with BTX-A or other pharmacological interventions would also be useful for therapists to assist with clinical decision-making.
A number of limitations exist in this systematic review. The first limitation was the authors’ inability to collect all full text and/or English versions of relevant studies. Some studies were inaccessible in English language and some abstracts were not yet published in full text form. As a result, there may have been relevant studies that were not included in this review. Another potential limitation of this review was the author’s decision to exclude studies if they included participants outside of childhood age range (0 to 18 years). This resulted in data on children within the accepted age range being excluded as it could not be dissected from adult populations. Although attempts were made to extract raw data pertaining to participants aged 0 to 18 years, if relevant data could not be isolated in the publication, the study was excluded altogether. Further, inclusion of studies with participants ranging from 0 to 18 years may limit the translation of findings to specific more refined age populations within this range. Publication of de-identified data sets (as is now being requested by many journals) may have been useful for addressing this limitation. The authors decision to record the effects of serial casting across multiple timeframes and introduce these into the meta-analyses was undertaken to enhance the effect size and opportunity for a conclusive result, however this created significant heterogenous samples for some analyses, suggesting a large degree of dissimilarity in the individual study results. To account for the significant heterogeneity, a random effects model was used when appropriate to assess both intra-study sampling errors and between-study variation, resulting in wider confidence intervals and more conservative findings. A different methodological approach to data synthesis and analysis may have led to even stronger findings when examining the effects of serial casting on each of the outcome measures.
Despite the above-mentioned limitations, there are also many strengths to the present review. The methodology conducted was thorough and comprehensive with two to three reviewers involved at every stage, ensuring the reliability of the results from this study. Additionally, this systematic review provided a meta-analytic approach to addressing the study aims whenever possible, which was not done in previously published systematic reviews or overviews investigating the same or similar topics. Another strength of this review was the authors’ decision to ensure quality of the results being synthesised by only including fair to good quality studies for meta-synthesis, and only analyzing outcomes if there was a minimum of five investigations for the meta-synthesis and a minimum of two investigations for meta-analysis. Although a consequence of these methods meant that some data relevant to the effects of serial casting were omitted from analysis and thus from the overall findings of the review, it ensured that the results presented, and conclusions drawn were from accumulated trustworthy sources. The major strength of this review was that it drew conclusions from a detailed meta-synthesis and further quantified findings of previous reviews by including a meta-analysis using data from the stronger methodological quality studies only, when it was possible. No previous systematic review exploring the effects of serial casting on lower limb function in children with CP has previously undertaken a meta-analysis to form conclusions, except for Kelly and colleagues who published a Cochrane protocol in 2008 [
25], however this systematic review was withdrawn from publication in 2017 due to being out of date. Since the beginning of 2008, there have been six additional relevant papers added to the empirical literature that were included in our review. More recently Novak and colleagues in 2013 [
17], published a broad systematic review supporting the use of serial casting to improve joint range in the lower limbs, however no findings were published in this review regarding the effects of serial casting on functional gait. Therefore, we feel that the present review provides new insights into the functional benefits of serial casting independent of BTX-A.
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