Cerebral palsy may lead to a number of bone, joint and muscle problems that effect walking (gait) and mobility. Spasticity or contractures of muscles can cause the knees to flex at the hip knee and ankle which can cause difficulty or increased energy requirement of walking. Internal rotation of the thigh bone, external rotation of the lower legs, and severe flat feet combine to limit the "push-off" ability to move forward, making walking slow. When the muscles are too strong on one side and too weak on the other side, the muscle imbalance can result in gait abnormalities or dysfunction