I commonly encounter patients with lower back pain who have been told their pain is the result of sacro-iliac joint dysfunction (SIJ dysfunction).
A diagnosis of SIJ dysfunction is based taking a verbal history and a number of movement and palpation tests that have been well documented within manual therapy textbooks.
Unfortunately, these tests demonstrate poor diagnostic accuracy and a lack of reliability.
For those interested in a thought provoking and scientific appraisal of SIJ dysfunction and SIJ pain, I suggested having a look at the link provided below.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2582421/