dancing, martial arts, or weight lifting. Genetics also play a role in this condition. It is infrequently seen in people of African descent whereas in northern Inuit people spondylolysis occurs in about 50% of individuals. Spondylolytic spondylolisthesis (vertebral slip) usually occurs at the L5-S1 region and much less frequently at L4-L5. Not all the factors leading to the development of a slip in young adults with bilateral pars defects have been fully elucidated. Forward slippage tends to occur more frequently in young females with a trapezoid-shaped L5 vertebral body and dome-shaped sacrum, and in patients with vertebral slip angle of greater than 50%. The pars defects decrease the ability of the motion segment to withstand anteriorly directed shear forces and thus lead to an increased mechanical stress at the vertebral growth plate. Hence, most of the slip progression occurs while the spine is immature and still growing and not after the spine has matured.
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