Of or pertaining to the loins and sacrum; such as, the lumbosacral nerve, a branch of one of the lumber nerves which passes over the sacrum (the triangular-shaped bone lying between the 5th lumbar vertebra and the coccyx, or tailbone).

Relating to the lower back area including the broad pelvic bone structure and associated nerves: The neurosurgeon explained to Stephen that the sacrolumbar operation for his back should make it possible for him to feel better.