The lumbar spine in the sagittal plane should maintain an alignment in which each vertebral body is aligned with the vertebral body above and below. In other words, the anterior inferior endplate of the vertebral body above should be aligned with the anterior superior endplate of the vertebral body below. Spondylolisthesis occurs when there is an anterior translation or “slippage” of one vertebral body relative to its caudal vertebral body. In most cases, symptoms associated with spondylolisthesis are chronic. The primary symptom of chronic spondylolisthesis is back pain, with or without leg pain. When spondylolisthesis occurs acutely in the setting of traumatic or metastatic tumors, patients can present with neurological examination deficits including a loss of bowel and bladder function. The classification system utilized to categorize the degree of subluxation of the vertebral bodies is the Meyerding Classification, which quantifies the percentage of subluxation of the vertebral body above on the vertebral body below. Classification of Spondylolisthesis is based on the degree of slippage in the lumbar spine. Grade 1 is less than 25%, Grade 2 is 25% to 50%, Grade 3 is 50% to 75%, Grade 4 is 75% to 100%, and Spondyloptosis is > 100% .
There are many causes of spondylolisthesis including congenital, degenerative, traumatic, pathologic, iatrogenic, and isthmic. Isthmic spondylolisthesis, which will be the topic of this discussion, refers to a defect in the pars interarticularis that then results in anterior subluxation over time, most commonly at L5-S1 followed by L4-5. The resulting anterior subluxation can produce back pain, central canal stenosis, and lateral recess or foraminal stenosis.