Design and reliability
This is, as far as we know, the first reported series of children with CP of a specified subtype, longitudinally followed with anthropometrics. The study was part of the prospective follow-up during five years of a consecutive, complete series of children with CP spastic diplegia with gross motor function classified at all levels (GMFCS I-V), who were operated with SDR during the first ten years at Lund University Hospital. When introducing SDR in 1993 we chose this practice-based evidence approach to evaluate the outcome [27, 28]. The aim was to collect feed-back data to improve our ability to choose the right intervention for each child at the right time .
This series may be of value for comparison with other series in the future, even though some of the children were undernourished and/or had other health problems. The presented pre-operative growth data are representative of the CP spastic diplegia subtype at the different GMFCS levels in a developed society and a health care setting with at least fairly good nutritional support, including gastrostomy and available specialists in paediatric gastrointestinal disorders and dieticians. Although the spasticity reduction through SDR may have influenced growth, the postoperative measurements indicate existing growth potential in CP spastic diplegia.
The anthropometric data included in our follow-up were the clinically used standard measurements of height/recumbent length and weight, the most precise anthropometric measures in typically developing children . The reliability of weight measurements is high, also in children with CP. In contrast, direct height/length measurements were regarded as impossible to use in the North American Growth in Cerebral Palsy Project (AGCPP). Knee height was chosen as a proxy at functional levels GMFCS III-V . The children in our study were without any significant scoliosis or severe joint contractures . The measuring was performed by two PTs used to children with CP. The children were well acquainted with the PTs and felt secure in the measuring and training sessions. The PTs could keep the children fully stretched, still and control that ankle, knee, hips and back were in the right position in addition to right position of the heel and head. Therefore we regard the measurements of stature as at least moderately reliable; at the best functional levels GMFCS I-II highly reliable, similar to the reference population.
As GMFCS and subtype-specific reference growth data were unavailable, we chose the growth charts of typically developing healthy children of the same age and gender in our country as a reference, when describing the growth of the study group. The reference population was > 3500 children born at term in 1973-75, i.e. before the "obesity epidemic". They were followed by longitudinal measurements from birth to late adolescence (> 14 times per child) [21, 22].
The computer-generated growth chart provided automatic calculations of child age, z-score for every measure and plotting without the common plotting errors of manually completed growth charts . The growth curves were examined by a paediatrician (LW) for each child to identify any errors in the measurements.
Twice as many boys as girls were selected for SDR, mainly reflecting gender distribution of CP spastic diplegia in our area (prevalence 1.3/1000 boys and 0.7/1000 girls) . Gender did not exhibit a significant effect on the BMI change during the follow-up (p = 0.75).
Consequences of weight deviations in CP
Childhood obesity is an increasing problem all over the world. It is associated with a higher chance of premature death and disability in adulthood mainly due to cardiovascular disease, diabetes, cancer and osteoarthritis . Increased obesity prevalence is reported in ambulatory children with CP: from 7.7% in 1994-1997 to 16.5% in 2002-2004 , similar to that seen in the general paediatric population .
Besides the above-mentioned association with severe long-term health consequences, overweight may cause activity limitations in CP. Simulated weight gain through a heavy belt was shown to have an immediate negative impact on energy costs of walking in children with CP . On the other hand, the NAGCPP study showed that weight < -1 SD was associated with poor health and low societal participation [3, 36].
Several previous studies have shown that children with CP are shorter and thinner than healthy children with typical development of the same age [e.g. [2, 16]]. The relative falling off in stature with age in children with severe functional limitations (GMFCS levels IV-V) in this study is consistent with previous reports [1, 3, 7, 16]. The slight catch-up of median height z-scores during the five years of follow-up in children with standing and walking ability (GMFCS levels I-III) in our study has not been described previously (Table 1). This could be a chance finding. When displayed as mean height z-scores at different ages, no such increase is seen with age (Figures 4-5). The growth potential in childhood CP is unknown, as all studies up to now include children with malnutrition and other health problems.
Overweight and obesity are defined as abnormal or excessive fat accumulation that may impair health. BMI provides the most useful population-level measure of overweight and obesity. At the individual level, however, BMI should be considered only as a rough guide, because it may not correspond to the same degree of fatness in different individuals . In children, the proportions of muscle mass and fat mass may vary with age, and it is conceivable that especially great variations may be seen in children with CP, by age and functional level.
Overweight, obesity and SDR
Children in this series were SDR-operated early in life. Their median weight and BMI z-scores increased with age, and the prevalence of obesity increased from 4% at median age 4.3 years to 15% five years later. If the spasticity reduction after SDR promoted weight gain through less energy requirement, it could be counteracted by increased physical activity, hypothetically the case in the GMFCS III children in this study, who reduced their median BMI. According to Figures 2 and 8 the mean weight and BMI z-scores increased again at six to seven years of age in GMFCS III. At this age all children in Sweden start school.
The accelerating mean weight z-scores at six-seven years of age shown in this study for all GMFCS levels are probably due to more physical inactivity in the school setting than during the pre-school years, with much more focus on activities in locomotion and mobility.
It is questionable whether the increased prevalence of obesity should be viewed as a complication of the SDR operation, as we do not know the "natural course" in non SDR-operated children with spastic diplegia. Available data are scarce, and include other CP subtypes. BMI > +2 SD was present in 6/106 children in Swedish children with bilateral spastic CP (spastic tetraplegia and diplegia) at mean age 7.1 years . The prevalence of obesity, defined as BMI over the 95th percentile, in ambulatory children (mainly spastic hemiplegia and diplegia) with CP was 14-16.5% according to anthropometric measures in a US gait laboratory during 1998-2004 . It is conceivable that the prevalence of obesity accelerates after 5-6 years of age in children with CP as in other children .