The coccygeus and levator ani are technically muscles of the pelvic floor, however, they are also muscles whose contraction forces cross the sacroiliac joint and therefore often tighten when a sacroiliac joint condition exists. The coccygeus attaches from the sacrum and coccyx to the ischial spine of the pelvic bone.
Bones of the Lumbar Spine and Pelvis
The low back is defined by the lumbar spine, composed of 5 vertebrae, named L1-L5. The pelvis is defined by the bones of the pelvic girdle.