It is important for the baby to pass through all developmental stages of a normal development. The normal development of the infant includes the backwards motion of the shoulder blade at the thorax. After birth, the shoulder blades lie relatively far to the side of the thorax and later move backwards. This makes breathing easier. Many shoulder muscles affected by the upper plexus lesion are necessary for this new positioning of the shoulder blade.
Because the shoulder muscles are paralysed, the infant does not learn to stabilise the body using the arms when in the prone position. Furthermore, normal muscles of the shoulder girdle are functionally disintegrated by the failure to learn the movement patterns. Learning to crawl, as a further step in development, and the further stabilisation of the shoulder girdle that it involves, for example, is essential for the normal development of the shoulder blade and of the other bones of the shoulder girdle and also of the thorax. Due to these developmental disorders, growth and the learning of movement sequences can be impaired, and areas of stiffness can develop in the different joint systems. Continual physiotherapy with specialised therapists therefore seems important, in order for movement patterns to be learnt correctly and age-appropriately.
Frequently, for example, an imbalance arises between flexing and stretching and between inward and outward-turning muscle systems. This results in corresponding impairments of the movement patterns, which in turn have effects upon the skeleton. We can, however, detect such imbalances in good time, in the framework of regular checks. The functions of the arm and hand can be further optimised by physiotherapy, electrical stimulation or secondary regulative operations.