Spastic cerebral palsy is the most common form of cerebral palsy, accounting for between seventy and eighty percent of all cerebral palsy cases. People with this condition have stiff muscles that remain in a state of prolonged contraction. Such muscle stiffness and contraction makes normal movement difficult, and can lead to permanent muscle and joint damage over time.

While the muscles of the arms and legs are most severely affected in spastic cerebral palsy, the extent to which they are involved may vary. One type of spastic cerebral palsy is spastic diplegia. In this form, muscles in both legs are affected, resulting in the legs turning in and crossing at the knees. When a person with spastic diplegia tries to walk, the legs are stiff and cross at the knees, causing the characteristic scissors gait. In another type of spastic cerebral palsy called spastic hemiplegia, the limbs on one half of the body are affected. This type of cerebral palsy may be detected when a doctor tests an infant for hand preference. Before the age of one year, babies do not usually show hand preference. However, in spastic hemiplegia, an infant favors the hand that is on the unaffected side of the body.

The movement defects in spastic cerebral palsy are managed by combining physical therapy and surgery. Muscles and joints are exercised to prevent them from falling into disuse. A combination of disuse and abnormal posture may cause some muscles to permanently shorten, thereby worsening a patient's range of movement and flexibility. Often, a substance that relaxes muscles, such as botulinum toxin or Botox, may be injected into a particular group of muscles in preparation for physical therapy or surgery. The spinal cord and nerves may also be operated upon to reduce the transmission of nerve impulses to certain muscles and thereby relax them. Orthopedic devices can help maintain limbs in their correct positions and improve movement.