In out-patient clinic, it seems to be common that most back pain arise from muscular origins rather than from skeletal origins. Most physicians have wished to diagnose lower back pain from the radiologic findings only. From clinical experiences and anatomical studies, I have gotten a different opinion from common sense about backaches. If I met a patient who had lower back pain around the posterior superior iliac crest(P.S.I.C.) area, I would had to search a trigger point in the erector spinae muscles at the level of thoraco-lumber junction rather than at the level of the painful site. It is why that sensory innervation over the posterior superior iliac crest area is the posterior primary branch of T12 spinal nerve running down through the erector spinae muscles. Pain on the iliac crest area is supposedly due to hyperirritability of the sensory nerve distributing to this area. Hyperirritability of the posterior primary branch of $T_{12}$ spinal nerve may be due to the spasm of the longissimus thoracis muscle in the erector spinae muscles at the level of the thoraco-lumbar junction. So finally, I would like to insist that spasmolytic treatment on the muscle at the level of the thoraco-lumbar junction would be better for pain relief around P.S.I.C. than treatment at the painful site only.