Spondylolysis is a unilateral or bilateral stress fracture of the pars inter-articularis, affecting one or more lumbar vertebrae. Repeated flexion, extension, rotation, and torsion, particularly in combination, are thought to be associated with the highest prevalence of spondylolysis.
Lumbar spondylolysis occurs in 6-8% of the general population, and is usually asymptomatic.4 The condition is two to three times more common in males than it is in females, and arises most frequently in late childhood or adolescence. 5 It is rare for spondylolysis to arise after the age of 20.1
Spondylolisthesis refers to the anterior slippage of one vertebra on the adjacent caudal vertebra. The majority of spondylolistheses are exclusively attributable to an abnormality of the pars inter-articularis, such as spondylolysis.4 15% of those with spondylolysis progress to spondylolisthesis.5 Spondylolisthesis is also produced by pathology such as facet joint incompetence.4
Spondylolysis and spondylolisthesis are radiological diagnoses, and both are common in the asymptomatic population. The prevalence of back pain is no higher among adults with spondylolysis and low grade spondylolisthesis,4 implying that an observation of either defect does not allow any inference to be drawn as to the source of a patients back pain. The first part of this article addresses spondylolysis, and the second addresses spondylolisthesis.