What is wrong with Clifford Chatterley?

Clifford Chatterley is an invalid. Constance Chatterley, at age 23, had married Clifford Chatterley, age 29, in 1917 during the war, when he was on leave from the war. He had returned to the war after their marriage. But he was shipped back "in bits," paralyzed from the hips down, and spent two years in the care of a doctor.