When grandma exclaims, ‘Look how much you have grown!’ she probably does not appreciate that she is referring primarily to enchondral bone formation occurring at the endplates of the vertebral bodies and the physes of the tibias and femurs. This, however, is a rather limited view of bone growth. Bones also grow in diameter and cortical thickness through the different process of appositional bone formation, and these aspects of bone growth are the more important determinates of a bone’s ability to resist fracture. But even a broader view of bone growth still leaves one with a limited perspective of growth. For example, a child’s growth is also reflected in increases in cardiac output, pulmonary vital capacity, and renal glomerular filtration rate.
Weight is typically used to supplement height as the means of monitoring a child’s growth. As a measure of growth, weight does reflect increases in bone mass, muscle mass, and the mass of the other organs, but obviously body fat is an additional component. A child’s growth is routinely monitored as a general reflection of the child’s health, the premise being that normal growth is healthy and if diminished then something is wrong that should be identified, and if possible, corrected. The view that some children would be considered healthier if their weight decreased while they grow, emphasizes the limitations of weight as a measure of growth.
Regardless of the complexity or simplicity of one’s view of growth, the greater issue is the importance one attaches to ‘normal’ growth. While it is axiomatic to say that normal children should grow normally, it is unjustifiably simplistic to assert that children who are not normal should also grow normally. This is abundantly clear in children with achondroplasia or Down syndrome, but very uncertain in children with quadriplegic cerebral palsy (CP). The true goal is to optimize the child’s health.
The importance one attaches to growth, and one’s goals for growth, should therefore be based on the strength of the link between growth and the many varied and complex aspects of health. Studies of this critical issue include that of Stevenson et al. who found in children with moderate-to-severe CP that greater growth (as assessed by measures including knee height, skinfolds, and arm muscle area) is associated with better health (as assessed by the number of recent health care visits, days of missed school, care providers missing work, etc.).1 But this association does not tell us whether better growth resulted in better health, or whether the better health resulted in better growth. Further, in their series even the group with the ‘best’ growth still did not have ‘normal’ growth. Whether ‘normal’ growth can or should be obtained in this population remains unknown.
So despite limited measures and uncertain goals we now turn our attention towards interventions to improve growth, and the intervention that is both the most invasive and potentially the most effective is gastrostomy. An American Academy for Cerebral Palsy and Developmental Medicine evidence report on gastrostomy published in 2003 in DMCN identified 10 studies assessing gastrostomy.2 The most widely and consistently reported finding was a gain in weight; none of the study designs were Level III or higher. Since that report there has been additional important work in the area, including but certainly not limited to that of Sullivan et al.3
Arrowsmith et al.4 look at multiple measures of growth including bone mineral content and total body protein in 21 children who had a mean increase in body weight of 50% following gastrostomy placement. As previously reported,2 the greatest change was in body weight, mostly as body fat. Increases in height, bone mineral content, and total body protein were also observed, but these measures relative to age-matched controls (i.e. z-scores) did not increase. It is known that height and bone density z-scores normally decline over time in children, so perhaps the lack of change following gastrostomy does in fact represent a positive treatment effect.
In summary, important steps in this area include first recognizing the complexity of growth; particularly, weight and even height are limited measures. This study by Arrowsmith et al. certainly contributes here. The second step is to establish goals for growth that are based on the link between growth and health. Here we have miles to go before we sleep.