Cerebral palsy (CP) is a clinical description and by definition; a permanent disorder of the development of movement and posture, causing activity limitation, attributed to non-progressive disturbances that occurred in the developing fetal or infant brain. The motor disorder in CP is often accompanied by disturbances of sensation, perception, cognition, communication, and behavior, by epilepsy, and by secondary musculoskeletal problems. This description gives no information about the children's functional ability, and it has been suggested that the diagnosis of CP should be used together with functional classifications. One of these classifications is the Manual Ability Classification System (MACS) that has been widely used in recent years, both in clinical practice and in research. However, further investigation is required to determine whether or not children remain at the same MACS level during development and growth and to establish if the MACS ratings have predictive value.
The MACS consists of five levels and was designed to classify how children with CP aged 4 to 18 years use their hands when handling objects in daily activities. Children at MACS level I handle most objects easily and successfully. At MACS level II, they handle most objects but with somewhat reduced ability and/or speed. Children at MACS levels III to V need assistance to different degrees. At MACS level III, children handle objects with difficulty and require help in preparing and/or modifying activities. Children at MACS level IV can handle a limited selection of easily managed objects in adapted situations. At MACS level V, children cannot handle objects and have severely limited ability to perform even the simplest of actions. Further descriptions of the MACS levels can be found online.
If an instrument such as the MACS shows outcomes that are stable over time, it could be used to predict future manual ability levels. Even though children's hand use may change as a result of increasing experience, development, interventions, or as the result of secondary complications, we expect most children to stay at the same MACS level over several years. This is because we do not expect changes to the extent that could generate a transfer across the fairly broad classification levels. The stability of MACS ratings may be influenced by either a child's possible change in manual ability or by possible inconsistencies within or between raters. In several studies, the inter- and intrarater reliability of the MACS has been found to be good to excellent between therapists as well as between parents and therapists, varying from 0.73 to 0.98 and 0.91 to 0.98 respectively.[2, 4-11] There is also evidence supporting the stability of MACS classifications over a short period. In a previous study, the intraclass correlation coefficient (ICC) was high (0.92) and 67% of the children remained at the same level over a period of 1 year when scored by caregivers.
The primary aim of this study was to evaluate the stability of MACS levels over time for children with CP. The secondary aim was to investigate whether MACS levels were less stable for younger than for older children, or if certain MACS levels showed lower stability than others.
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In total, 1267 children (746 males, 521 females) fulfilled the inclusion criteria. The mean age at the time of their first MACS classification was 6 years 6 months (SD 2y 11mo; Table 1). The number of ratings for each child varied between two and four, with at least 12 months and at most 5 years from first to last rating. In all, 3694 MACS registrations were included in this study. All MACS levels were represented and the distribution of MACS levels and age at first classification is presented in Table 1. Information on sex, diagnosis, and the Gross Motor Function Classification System (GMFCS) level were extracted from the child's latest registration (Table 1). Some children had not yet received a specific sub-diagnosis of CP and were included in the category of unspecified CP.
Table 1. Demographic characteristics of participants in terms of age and MACS level at first classification
| ||Participants n (%)||Sex||MACS level|
|15–17||21 (2)||11||10||9|| ||6|| ||6|
|Spastic unilateral||371 (29)|| || ||155||141||58||17||0|
|Spastic bilateral||419 (33)|| || ||146||76||71||56||70|
|Dyskinetic||145 (11)|| || ||7||8||20||36||74|
|Ataxia||79 (6)|| || ||25||26||13||12||3|
|Unspecified||253 (20)|| || ||81||55||37||35||45|
|Total (%)||1267||746 (59)||521 (41)||414 (32)||306 (24)||199 (16)||156 (12)||192 (16)|
| || || || ||GMFCS level|
|Total (%)|| || || ||562 (44)||202 (16)||116 (9)||185(15)||186 (15)|
Stability of two MACS ratings 1 year apart
An excellent agreement was found with an ICC of 0.97 (95% confidence interval [CI] 0.97–0.97) between two ratings 1 year apart for all 1267 children. Eighty-two percent of the children were classified at the same level in both ratings. The percent agreement and the distribution of deviant ratings are seen in Table 2. In cases where the ratings differed, it was generally only a difference of one level. One hundred and twenty-three children were scored to a higher level (indicating lower ability) on the second rating occasion, and 103 children were scored to a lower level (indicating higher ability), but there was no systematic direction for the differing ratings (McNemar's test for paired proportions p=0.13). There was almost no difference in stability between the younger (4y) and older (≥10y) age groups with an agreement of 80% and 82% respectively.
Table 2. MACS levels for two ratings with 1y between ratings (n=1267)
| ||MACS second rating|
|MACS first rating|
|I|| 364 ||43||3||4||0||414|
|II||36|| 234 ||33||3||0||306|
|III||3||23|| 148 ||23||2||199|
|IV||0||4||12|| 124 ||16||156|
|V||0||0||1||24|| 167 ||192|
Stability of two MACS ratings 3 to 5 years apart
Thirty-five percent of the group (n=445) had been classified with the MACS over a period of 3 to 5 years. The ICC was 0.96 (95% CI 0.95–0.97) and the percent agreement was 78% between the first and last ratings. The distributions of classification for this group are found in Table 3. Disagreement between ratings mostly concerned one level of difference. Fifty children scored at a higher level and 47 children scored at a lower level at the time of the last classification (McNemar's test for paired proportions p=0.84). Age did not influence the scoring and there was similar stability between age groups with a percent agreement of 75% for children 4 years of age and 77% for children 10 years of age or older when first classified. Thus, the MACS levels were equally as stable whether the first classification took place at a younger or older age.
Table 3. MACS levels for children at the first and last ratings out of four ratings performed over a period of 3–5y (n=445)
| ||MACS last rating|
|MACS first rating|
|III||0||14|| 43 ||11||0||68|
|IV||0||2||2|| 35 ||9||48|
|V||0||0||1||7|| 51 ||59|
Stability of four MACS ratings
Agreement between the four ratings was also excellent with an ICC of 0.95 (95% CI 0.94–0.96) for ratings performed about 1 year apart over the course of 3 to 5 years. The percent agreement between the four repeated ratings was 70% and this showed that most children remained in their initial MACS level in all subsequent ratings. When percent agreement was calculated separately for unilateral CP and bilateral CP, the agreements were 72% and 69%, respectively. For children who received different ratings, this commonly involved a change of just one step in the classification. Only 10 children (2.2%) changed two levels in the four-rating model (Table 4). No systematic difference of the scoring at different rating times was shown (Friedman's test p=0.69). When the agreements were analyzed for each MACS level separately, the stability was very good for MACS levels I and V. The stability for levels II to IV was somewhat lower but still considered good as estimated Fleiss' kappa (Table 5).
Table 4. Distribution of the change of MACS levels in children with four repeated ratings over 3–5y (n=445)
|No. of levels changed||N of children||%|
Table 5. Stability for each MACS level across four ratings
|MACS||N of children||Kappa||SE|
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The ICC was, in general, excellent and the agreement was high in the different models. This shows evidence for the high stability of children's MACS levels over time. When comparing results between two ratings, the percent agreements were 82% for ratings performed 1 year apart and 78% for those performed 3 to 5 years apart. Even the four repeated MACS ratings over a period of 3 to 5 years showed an agreement of 70%. Furthermore, there were no differences in stability over time between younger children who were 4 years old and children who were 10 years or older at the time of their first classification.
The stability of the MACS over two classifications with 1 year in between showed a somewhat higher stability in the current study (ICC=0.97) compared with that found by Imms et al. (ICC=0.92). In that study, all children were 11 to 12 years old, but the biggest difference was that the MACS levels were rated by the children's caregivers in a postal survey but in the current study the rating was performed by healthcare professionals in collaboration with the children's parents. The MACS has been used in Sweden since 2005 and professionals might be more familiar with the MACS compared with the Australian caregivers in the study by Imms et al. who were probably scoring the children for the first time. Familiarization with a classification system has previously been suggested to influence the results, and has been mentioned as a possible reason for why the GMFCS showed higher reliability in the second study compared with the first study.[21, 22] The stability of the MACS ratings in the current study is approximately equivalent to that reported for the GMFCS in which 73% of the children remained in the same level when followed over several years.
In cases where the MACS level changed over time, the change was commonly to the next closest level in either direction. Thus, there was no tendency for systematic change over time. When investigating whether certain MACS levels were more prone to change than others, we used the four repeated ratings and their standard deviations as a measure of variance and found that levels I and V were the most stable. The stability was somewhat lower for levels II to IV. This is possibly because change can occur in two directions for these three levels, but for levels I and V changes can occur in only one direction.
It might have been expected that younger children would be more susceptible to change and that their MACS levels would be less stable over time compared with children who were followed from an older age. However, the stability for children 4 years of age and the stability for children of 10 years and older showed similarly high levels. This aligns well with findings of interrater reliability being equally high for different age groups of children. Less stability was seen for the GMFCS in younger ages when comparing children younger and older than 6 years of age, and when comparing children younger than 4 years of age with older children.
The usefulness of a classification system as a predictive instrument depends on its stability over a long period so it was of interest to compare agreement between two MACS ratings with different time periods between ratings. We found that the time between the first and second ratings did not significantly affect the agreement because there was only a very small difference between ratings repeated after 1 year compared with those repeated after a period of 3 to 5 years. This finding also indicates that the MACS may be stable even with different raters, as although it may be likely that the same rater completed the MACS at the end of a 1-year period, over a 3- to 5-year period it is more likely that different raters will have completed the MACS ratings.
This study indicated that children predominantly remain in the same MACS level over time. This is not surprising, for two reasons. Firstly, change between levels is not expected because of the broadness of each of the five categories. These levels are meant to cover the whole range from very mild to very severe functional limitations in the population of CP. Secondly, age-related development is embedded in the MACS, as the handling of objects always refers to objects that are relevant for the child's age. Thus, the expected changes in skill level that are related to age will not make children change their MACS level. The levels instead describe distinct differences between how objects are handled and the amount of assistance needed to handle these objects. In the light of this, it is important to acknowledge that the MACS is a very useful tool for describing functional levels of manual ability for individuals or groups and that this information has a predictive value. However, the MACS is not intended to be an evaluative tool, and MACS levels are not expected to be sensitive to change after interventions and should thus not be used as an outcome measure.
In this study sample there were varying numbers of children at different ages and MACS levels and this reflected the distribution of children included in the CPUP register. The reason for the higher proportion of younger children in this study is the fact that children enter the register at early ages. Since 2005, all regions in Sweden have been included and the register is now based on the entire national population of children born in 2000 or later. Nevertheless, the distribution of MACS levels in this study seems to be comparable with the Victorian Cerebral palsy register study in Australia and a population-based study in Sweden in which more children were found in levels I and II compared with levels III to V. Another limitation of the study is that the child's previous result could have been known to the therapist. However, when completing the CPUP assessments it is recommended that comparison with historical assessments should be done only after completing the annual CPUP evaluation. The stability of MACS has in this study been reported for a time period up to 5 years. Further investigation of the longitudinal stability over periods longer than 5 years is also needed. The CPUP register provides an opportunity for future studies of this issue.
In conclusion, the MACS has previously been shown to demonstrate evidence of validity and reliability. Our study now shows that the MACS is also fairly stable over time and has predictive value.