You raise an interesting question that has been studied worldwide. Since doctors must decide when someone is disabled, they want to be as accurate as possible. However, when back pain is present, humans tend to have an emotional response to that pain.
Sorting out what is psychological and what is biological isn’t always easy. Doctors do have some tools to use. One is a series of five movements called Waddell’s Nonorganic Signs. Patients who test positive for this test show changes in their behavior that aren’t present when symptoms are caused by tissue injury.
Another test is the McGill Pain Survey. In this test, patients choose various words listed to describe their pain. Certain words, such as “torturing,” “killing,” or “dreadful” are linked with strong emotion. Other words such as “sore,” “aching,” or “heavy” are used to describe muscular pain.
Other similar tests can be used with patients depending on the location of their injury. Formal, psychologic testing is also possible.