Lumbosacral

[Sarah]

Of or pertaining to the loins and sacrum; as, the lumbosacralnerve, a branch of one of the lumber nerves which passes over thesacrum.

[Sarah]

relating to the lower back and sacrum (= the large triangular bone at the bottom of the spine) :

[Sommer]

of or relating to or near the small of the back and the back part of the pelvis between the hips