What are the differences between spastic and flaccid paralysis?

Muscle tone. Spastic means tight muscles, flaccid is loose and relaxed muscle. Different causes for each.
Amount of tone. The difference between the two is the tone in the limbs. In spastic paralysis the tone is increased, the upper limb is flexed the fingers contracted. The lower limb is somewhat stiff and may support ambulation. In flaccid paralysis tone is markedly reduced. The arm when held up drops, as does the leg; no resistance against gravity. The leg will not support ambulation even with an assistive device.