Imagine building a tower, and stacking one block on top of another, with a layer of mortar between each block. If you were building the human spine, the blocks would be the vertebral bones, and the intervertebral discs would serve as the mortar between the spinal bones. Though the architecture of the human spine is a little more complicated than this, this description illustrates the main components of the spine, and the importance of each structural component, relative to the other. For the spinal bones (vertebrae) and other structures of the spine, such as the joints and soft tissues, to remain healthy and supported, all of its elements must remain in proper alignment, relative to one another. In the condition of Isthmic Spondylolisthesis, one of the vertebral bones slips forward or backwards relative to the one below it. This skidding of the spinal bone occurs because of a degenerative condition that occurs at the back of the spine, which normally connects links one vertebra to the one above or below it. Due to osteoarthritis or weakening of the bone, a fracture occurs where the two spinal segments normally connect to each other, and the resulting instability breaks this previous connection. The resulting instability causes the vertebral bone to slip forwards or backwards.
The section of the bone that fractures the most often to move the vertebra out of alignment is the pars interarticularis. The pars interarticularis may become prone to fracture due to conditions such as osteoporosis or repetitive stress. The repetitive stress fracture at this portion of the bone often occurs early in life, though it is not until much later that people experience continued symptoms related to this condition. Typically, this fracture occurs when someone is between the ages of 5-7. The person may experience acute pain related to this condition shortly after the fracture. The person may experience another short wave of symptoms during adolescence. The person may then experience chronic pain related to this condition in adulthood. Symptoms of Isthmic Spondylolisthesis include:
- A deep ache in the lower back (lower back pain)
- Referred pain, or pain that spreads from the lower back and into the buttocks and back of the thighs
- The radicular pain may spread beyond the back of the thigh and possibly to the lower leg and foot
- The patient may experience tingling, numbness, or a tired sensation in one or both legs. These symptoms may be present at rest, but is more likely to increase after walking or activity.
- These pain and other neurologic symptoms (e.g. numbness, fatigue, tingling) may be exacerbated by extending the back, or bending backwards.
- Pain that becomes worse when walking and standing
Spondylolisthesis Causes. There are many structures that allow for movement of the various segments of the spine, while also maintaining the stability and structural cohesion of the spine. Any weakness of the muscles that support the spine, or degeneration to the soft tissues that hold it in its proper condition, could contribute to this condition. Degenerative changes to one section of the spine could make other portions vulnerable, such as the pars interarticularis. In other cases, the spine is generally healthy, but a fracture occurs on the pars interarticularis due to violent bends of the spine, as could occur in athletic activities such as football or gymnastics. Hyperextensions of the back, which occurs during violent collisions in sports or activities that require extreme back bends, are likely to cause this condition. The condition of Isthmic Spondylolisthesis is a two step orthopedic problem, because it involves both the fracture as well as the resulting slip of one vertebral segment over the other. When the fracture occurs without the resulting slip of the vertebra, the condition is known as spondylolysis. The condition gets its name from the fact that the pars interarticularis is also known as the isthmus.