The lumbar spine is made up for five vertebrae (L1-L5) separated by five discs. The discs are much like shock absorbers, in that they absorb the load coming down from all the weight above. They allow the bones to permit movement such as bending twisting, lifting and rotation because they act as a pivot point. When you jump off of something, it’s your discs and the spines curvature that absorb the shock like a strut in a car absorbs bumps in the road.
Another important thing to understand about a normal disc is that it is like a hydraulic system. Think of a car tire, the center is filled with air, whereas your discs are filled with fluid. If you slice a tire, air is going to leak out and deflate the tire. If the disc is punctured, fluid is going to leak out and cause pain. Imagine you punctured a tire but not all the way through and while driving along you hit a bump causing the tire to blow. A similar thing happens with your discs. The physical or chemical stress of everyday life can weaken the outer layer of the disc rendering it unstable. This is why when most people have their back “go out” they really weren’t doing much; typically bending forward to pick up a pen off the floor is enough to cause the disc to bulge in some cases.
You may have heard the term “slipped disc” used to describe a low back injury. Discs do not actually “slip”. Rather, they may herniate or bulge out from between the bones. A herniation is a displaced fragment of the center part or nucleus of the disc that is pushed through a tear in the outer layer or annulus of the disc. Pain results when irritating substances are released from this tear and also if the fragment touches or compresses a nearby nerve. Disc herniation has some similarities to degenerative disc disease and discs that herniate are often in an early stage of degeneration. Herniated discs are common in the low back or lumbar spine.