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Spondylolysis and Spondylolisthesis
The bones of your spine are arranged to give your spinal column stability. Damage or defects within the supporting structures of your lumbar spine (low back) can be a source of back pain. A crack in the bony ring of your spinal column is called spondylolysis. If the crack occurs on both sides of the bony ring, your spine is free to slip forward, which is a condition called spondylolisthesis. About five to six percent of the population is affected by these two conditions.
Spondylolysis describes a defect in the bony ring of a vertebra in your spine. It mainly affects the lowest lumbar vertebra. The bony ring, formed by the pedicle and lamina bones, protects your spinal cord and spinal nerves. The bone is weakest between the pedicle and lamina, an area called the pars interarticularis or “pars” for short. A pars defect is believed to be a stress fracture. A stress fracture happens from repeated strain on a bone. At first your body is able to heal the damage. If the repeated strains happen faster than your body can respond, the bone eventually fractures. People are not born with spondylolysis. It commonly first appears in childhood. Football linemen and gymnasts are affected the most.
Spondylolisthesis describes a vertebra that has slipped forward on the vertebra below. This usually occurs when a vertebra has a bony defect (spondylosis) on both sides of the bony ring. A crack on both sides of the bony ring separates the facet joints from the back of your spinal column. The facet joints can no longer steady the vertebra. The vertebra on top starts to slide forward, slowly stretching the disc below the damaged vertebra. In adults, there is usually no danger that the vertebra will slide off the vertebra below. But teenagers sometimes have a unique type of spondylolisthesis in which one vertebra slips forward and slides completely off the vertebra below.
Spondylolysis and spondylolisthesis can both be a source of low back pain. Yet having one of these conditions does not mean you are certain to have back problems. It does put you at higher risk compared to people who don’t have them. These conditions can cause mechanical pain–the kind or pain that comes from within the moving parts of your spine. They can also cause compressive pain, which is from pressure on the nerves in your low back.
Pinched or irritated nerves produce compressive symptoms. This occurs in spondylolysis when a lump of tissue forms around the crack. This is your body’s way of trying to heal the stress fracture. The lump can cause pressure on the spinal nerves where they leave your spinal canal. A pinched nerve, called radiculopathy, can also happen in spondylolisthesis when the vertebra slides forward and squeezes the nerve. The forward slip of the vertebra also makes your spinal canal smaller, leaving less room for your nerve roots.
Pressure on the nerve can produce pain that radiates all the way down to your foot. It can also cause numbness in your foot and weakness in the muscles supplied by the nerve.