A L5-S1 diffuse posterior disk bulge occurs when a spinal disc between vertebra L5 and S1 compresses a nerve adjacent to it, explains the Laser Spine Institute. Due to pressure on the central core, the disc expands to the outer rim, causing the disc to bulge.
This is a very common type of back problem and typically creates little pain in younger patients, says the Laser Spine Institute. Over the years, the outer walls of the intervertebral discs weaken. When the bulging disc reaches a nerve, it causes pain. Most pain from the L5-S1 occurs in the lower back, hips, buttock, legs and feet. When a bulging disc hits one or more of the six spinal nerves, sciatic pain occurs.