S33: Dislocation, sprain and strain of joints and ligaments of lumbar spine and pelvis

S33.6: Sprain and strain of sacroiliac joint

There is a joint between the sacrum and the pelvis. This joint is so firmly connected by ligaments that it can hardly move. In your case, this joint has been strained or your ligaments have been overstretched.

As a result you may have some back pain or be unable to move properly.