You might want to try to use Treatment Based Classification system as developed by Anthony Delitto and others at the University of Pittsburgh. Here's an article you could look up which may be helpful to you:

Subgrouping patients with low back pain: evolution of a classification approach to physical therapy
J Orthop Sports Phys Ther. 2007 Jun;37(6):290-302

Based on the info you provided, I cna't see that you performed adequate testing to either rule in or rule out the lumbar spine. Until you do that, I don't think you can impliate the Wikipedia reference-linkSIJ. When/if the lumbar spine is clear, I'd focus on pain provocation tests for the SIJ rather than any palpatory/alignment tests.