Lumbosacral spondylolysis (lumbar spondylolysis) is a unilateral or bilateral defect of the pars interarticularis that affects one or more of the lumbar vertebrae. See the images below.
Radiograph of L4 defect in the pars interarticularis.
Computed tomography scan demonstrating defects in the left and right pars interarticularis.
The term spondylolysis is derived from the Greek words spondylos, meaning vertebra, and lysis, meaning break or defect. Numerous hypotheses have been proposed on the etiology of lumbosacral spondylolysis (lumbar spondylolysis), as follows:
Separate ossification centers
Fracture during postnatal life
Increased lumbar lordosis
Impingement of the articular process on the pars articularis
Weakness of supporting structures
Pathologic changes in the pars articularis
Dysplasia of the pars interarticularis
However, mechanical factors are widely believed to be the cause or at least the trigger of the development of lumbosacral spondylolysis (lumbar spondylolysis), especially when congenital abnormalities are present.
Moreover, lumbosacral spondylolysis (lumbar spondylolysis) is argued to be related to the human erect posture and lumbar curve.
Ambulation may have a role in the genesis of lumbosacral spondylolysis (lumbar spondylolysis) because no known cases exist in nonambulatory patients.
As an acquired condition, no reports exist of its occurrence in stillborn fetuses or in the newborn.
Heredity is also implicated.
When the defect in the pars interarticularis is not associated with a forward displacement, the term spondylolysis applies.
The term spondylolisthesis is derived from spondylos and listhesis, meaning movement or slipping, and refers to the slipping forward of one vertebra on the next caudal vertebra (see the image below).
Lateral radiograph of the lumbar spine shows spondylolysis at L5 with spondylolisthesis at L5 through S1. On this single view, it is not possible to determine if these pars defects are unilateral or bilateral. Oblique views may help resolve this issue.
Lumbosacral spondylolysis (lumbar spondylolysis) is most common at L5, accounting for 85% of all cases,
and may be observed as high as L2.
Therefore, a slip is most common at the level of L5 slipping forward on S1. Lumbosacral spondylolysis (lumbar spondylolysis) is the cause of the most common type of spondylolisthesis.
Moreover, Ariyoshi et al reported a case of lumbosacral spondylolysis (lumbar spondylolysis) that occurred at 3 sites in L5 that involved the bilateral pars interarticularis and the center of the right lamina.