1. A concept of the natural history of motor development in children with spastic paraplegia and diplegia has been presented, based on a study of motor development tests.
2. The severity index, the months of motor development at the chronological age of three years, can be used to prognosticate the child's potential to walk. The prediction is reasonably accurate at the age of three years. The severity of involvement in the lower extremities is the most important determinant of eventual skill in walking.
3. Additional parameters have been examined and correlated with the prognosis for walking. Hip dislocation or seizures are significant deterrents to walking. Prognostication of ambulatory potential on the basis of upper-extremity motor involvement, intelligence, or birth weight is less reliable.
4. The effect of surgery on the prognosis for walking has been determined by comparing surgical procedures performed on patients with comparable motor involvement.
5. The maximum anticipated level of walking skill can be predicted by the severity index. A program of management has been formulated to achieve these ambulatory goals.