"L" TO PAY
'(<a href="http://www.j-archive.com/media/2007-10-19_J_16.jpg" target="_blank">Sarah puts her back into this clue</a>) Most back pain is in the area commonly called the lower back; medically, it's made up of the 5 vertebrae classified as <a href="http://www.j-archive.com/media/2007-10-19_J_16a.jpg" target="_blank">these</a>'
lumbar vertebrae