Pain Management as a specialty is concerned with the prevention, evaluation, diagnosis and treatment of painful disorders. The diagnosis relies on a thorough history and pain-oriented physical examination, including interpretation of diagnostic tests, and may require specialized diagnostic and therapeutic procedures.
The simple answer is that he was not always as disabled as he is today. Stephen Hawking was diagnosed with motor neurone disease in 1963. The doctors initially gave him two years to live but the disease's onset was not as rapid as they had expected. Two years later, he was still walking, albeit with a stick. Hawking was married to his first wife, Jane Wilde, on the 14th of July 1965.
Books: Stephen Hawking: the man who mistook his wife for a nurse. When Jane Wilde married a young research student named Stephen Hawking in 1965, she already knew he was seriously ill. A schoolfriend broke the news a couple of years before, saying that Stephen was suffering from some terrible, paralysing, incurable disease.