Yes, it is. The pelvis and base of the spine are composed of a number of bones that, like in the skull, are fused together. The base of the spine (sacro-iliac joint) can be vulnerable to both forms of arthritis, osteo and rheumatoid.
I meant to add that hip deterioration is often mistaken for pelvic pain because the hip joint angles in toward the groin/pelvis at the top of the thigh bone. If you're having pain in the "leg crease" between your thigh and pelvis, that's your hip joint.
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