Anatomy & Physiology
The spine is made up of a series of connected bones called “vertebrae.” In about 5 percent of the adult population, there is a developmental crack in one of the vertebrae, usually at the point at which the lower (lumbar) part of the spine joins the tailbone (sacrum). It may develop as a stress fracture. Due to the constant forces the low back experiences, this fracture does not usually heal as normal bone. This type of fracture (called a spondylolysis) is simply a crack in part of the vertebra (Figure 1) and may cause no problem at all. However, sometimes the cracked vertebra does slip forward over the vertebra below it. This is known as adult isthmic spondylolisthesis.
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