Cerebral palsy can be classified into four types: spastic, athetoid, ataxic and mixed. Spastic cerebral palsy is the most common form, accounting for between 70 and 80 percent of all cerebral palsy cases. Limb muscles are stiff and remain permanently contracted. This form of cerebral palsy is further subdivided depending on which limbs are affected. Both legs may be affected, turning in and crossing at the knees. This is called spastic diplegia, characterized by the