Impact on the Spine
SMA can weaken the muscles that support the spine and without this support, the spine can be pulled by gravity and curve. It is estimated that as they grow, 60-90% of non-sitters and sitters develop a spinal curvature, as do 50% of walkers.
When the spine curves sideways into a “C” or “S” shape it is called a scoliosis. When the spine bends forward it is called a kyphosis. At the same time as the spine curves, there are changes to the chest wall and rib cage which reduce the space available for the lungs to grow and for breathing. Therefore, it is important to monitor everyone who has childhood onset SMA for the possibility of scoliosis. Spinal curvature is best monitored by an x-ray of the individual’s whole spine so the curve can be measured. The measurement used is called the Cobb angle. For those who can sit or walk, the X-ray is taken in the most upright sitting or standing position they can manage. Those who are non-sitters should have their x-ray while they are lying flat. Non-sitters and sitters with a Cobb angle greater than 20o should be rechecked every six months until their bones are no longer growing, which is when they reach what is known as skeletal maturity. After that they should be checked every year, as spinal curvature can still progress into adulthood.