Schreumann's disease is traction epiphysitis of vertebral bodies, which make up the spine. The patient presents with a rounded back with pain and rigidity. It happens in susceptible boys mainly and is a self-limiting problem, till the growth is complete.
The object is to prevent an increase in kyphotic deformity (round back) which is usually responsive to proper exercises, and using a brace (orthosis) if that alone is not working. Surgery is required in a very small percentage of cases. Your grandson should be religiously following the advice of his paediatrician. Repeat the exercises.