Spondylolisthesis describes the anterior displacement of a vertebra or the vertebral column in relation to the vertebrae below. It was first described in 1782 by Belgian obstetrician, Dr. Herbinaux. He reported a bony prominence anterior to the sacrum that obstructed the vagina of a small number of patients. The term “spondylolisthesis” was coined in 1854, from the Greek “spondyl” for vertebrae and “olisthesis” for slip. The variant "listhesis" is sometimes applied in conjunction with scoliosis. These "slips" occur most commonly in the lumbar spine.
A ''hangman's fracture'' is a specific type of spondylolisthesis where the C1 vertebra is displaced anteriorly relative to the C2 vertebra due to fractures of the C2 vertebra's pedicles.
In the late 1890s, several cadaver studies demonstrated the characteristic pars defect of isthmic spondylolisthesis, leading to many different theories concerning the etiology of the defect. The first theory proposed a failure of ossification during embryonic development, leading to a pars defect at birth, which then progressed to an isthmic slip after the infant began ambulating. Following the development of the Roentgenogram in 1895, population X-ray studies showed that isthmic spondylolisthesis is, in fact, quite common. A population study by Fredrickson, et al. demonstrated that the pars defect began to appear around age six and became progressively more common until age 16. After age 16, the incidence fell and rarely developed after adolescence. This study confirmed that the pars defect is the result of a defect in the cartilaginous anlage of a vertebra but not apparent at birth. It is currently thought that the defect develops from small stress fractures that fail to heal and form a chronic nonunion. There have been reports that the defect is more common among athletes who participate in sports with repeated hyperextension, such as gymnastics, ballet, and American football.
Spondylolysis also runs in families and is more prevalent in some populations, suggesting a hereditary component, such as a tendency toward thin vertebral bone. Spondylolysis is the most common cause of spondylolisthesis. The hereditary factor (mentioned above) is quite notable, since the frequency of spondylolisthesis among Inuit is 30–50%. (This statistic is controversial, however, because further anthropological studies have shown that the occurrence of spondylolysis in Inuit people living in civilized communities is within the normal variancy at 7%. These people are hereditarily linked to the study group showing ~40%. It is theorized that the nomadic Inuit have a higher incidence of spondylolysis due to trauma acquired as infants by being carried in an amauti. While in an amauti, the baby is put into compressive extenstion with each step taken by the mother. Also, all other studies have shown a normal variance of spondylolysis within cultures of 6-10%, further suggesting that spondylolysis is an environmental abnormality and that a hereditary tie is very unlikely).
Further Reading
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