Mobilizations of the asymptomatic cervical spine can reduce signs of shoulder dysfunction in adults.
That is the title of the article in pubmed that looked at people with shoulder pain, but absolutely no neck pain. After the neck was examined and adjusted, the painful abduction arc of the shoulder was reexamined in different people and it was much better in terms of ROM and in a pain scale. It goes to show that the body is one piece as Dan John is fond of saying. Treat the body, not just the pain.
Here is the article from pubmed.