By Dr Ananya Mandal, MD
Normal development of bones in a child is a complex process that needs the help of normal muscle tone and structure. Due to changes and abnormalities in muscle tone present in patients of cerebral palsy there may be significant problems in bones of children with this condition.
Physical deformities of bones
Due to increased muscle tone, as seen in spastic cerebral palsy, the shafts of the bones are often thin. The long bones also grow in a twisted or spiral form. Despite thinning of the shafts of the bone (also known as the diaphysis), the metaphyses often appear quite enlarged. There is ballooning of the metaphysis. In addition, some bones may be longer than others. For example, a leg may be longer than the other due to growth disparities.
Due to motor difficulties and lack of movement, there is lack of use of the muscles and joints. Due to this there may be atrophy or thinning and drying up of articular cartilage. This leads to narrower joint spaces. Depending on the severity of spasticity there may be various forms of joint deformities. This could be angular or curved in form.
The vertebral bodies of the spine develop with the help of gravitational forces and loading that is applied vertically as a child bears his or her weight upright. If there is lack of movement of the spine in upright form there may be proper and/or full bone and skeletal development due to spasticity and an abnormal gait. This shortens the height of patients with cerebral palsy as the vertebral bodies do not get the chance to grow to their full extent.
Changes in bone mineral density
In children with cerebral palsy there may be low bone density. It is known that children with cerebral palsy may be prone to bony fractures due to mild or no trauma (atraumatic pathological fractures) due to reduced bone mineral density.
The bone mineral density varies among the four different groups of cerebral palsy patients – those who are mobile with an abnormal gait, mobile with assistance, non-mobile but weight bearing, non-mobile or weight bearing.
Causes of low bone mineral density among children with cerebral palsy may be due to various causes including:
low intake of minerals like calcium
low nutrient intakes due to difficulty in feeding or chewing, dysphagia (difficulty in swallowing), vomiting, and constipation
abnormal vitamin D metabolism in those treated with anticonvulsants for associated epilepsy - in addition, most children with cerebral palsy are housebound and have reduced sunlight exposure, and consequently, reduced serum vitamin D concentrations
Children with severe motor disability in addition have a higher risk of osteoporosis. Since weight bearing and movement is reduced there is hinderance in normal growth and development of bones.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)