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Spondylolisthesis is the anterior or posterior displacement of a vertebra or the vertebral column in relation to the vertebrae below. The variant "listhesis," resulting from misdivision of this compound word, is sometimes applied in conjunction with scoliosis.[1] These "slips" (aka "step-offs") occur most commonly between the fourth and fifth vertebrae of the lumbar spine. Researchers believe the vertebral slipping occurs when abnormal stress is applied when the lumbosacral joint is in a straight and stable position. The compressive stress and/ or degeneration of the vertebrae cause the top vertebrae to slide forward over the lower vertebrae, resulting in the vertebral slip. A hangman's fracture is a specific type of spondylolisthesis where the C2 vertebra is displaced anteriorly relative to the C3 vertebra due to fractures of the C2 vertebra's pedicles.







Epidemiology
Spondylolisthesis occurs roughly in 5% of children and 7% of the adult population. Researchers have found that the condition occurs four times more often in females and three times more often in blacks than in whites. According to the Agency for Healthcare Research and Quality, 13,627 people were diagnosed with spondylolisthesis in 2011. This population ranged from ages 1-85+ with 49.05% in the 45-64 age group and 62.82% female patients. The average length of stay was 3.4 days and average costs were $24,090. In 2010 approximately 15,628 people were diagnosed with Spondylolisthesis. Diagnosed patients varied in ages from 1-85+. The majority of the patients fell in the 45-64 age range (45.34%) and 61.48% were female. The average length of stay was 3.6 days and average costs were $28,583. Based on these results from 2010 to 2011, the incidence of spondylolisthesis seems to be decreasing. The average total number of patients, average length of stay in the hospital, and average costs decrease slightly from 2010 to 2011.

Risk Factors
Factors that increase the risk of acquiring spondylolisthesis include a presence of spondylolysis, spina bifida, young age, vertebral wedging, female gender, and hyperlordosis. Patients with spondylolysis, degeneration of the intervertebral discs, are at a 5-70% greater risk of developing spondylolisthesis depending on their risk factors. Spondylolysis (a defect or fracture of the pars interarticularis of the vertebral arch) is the most common cause of spondylolisthesis. This is not to be confused with a slipped disc, where one of the spinal discs in between the vertebrae has ruptured. Avoiding contact sports and high-intensity activities can also reduce the risk of spondylolisthesis.