■he term spondylolysis means breakage within the vertebrae. Spondylolysis refers to a unilateral or bilateral fatigue fracture that occurs in the pars interarticularis (the osseous bridge between the superior and inferior articular facets). About 6% of adults age 18 and older may have bilateral spondylolysis. The condition occurs most frequently at L5, with decreased incidence in L4 and even lower incidence at other sites. It is more common in males and appears in the first or second decades of life, mostly during adolescence. Spondylolysis is thought to occur due to repeated stress that leads to a "fatigue fracture" of the pars interarticularis. This region corresponds with the neck of the "Scot-tie dog" on oblique films of the lumbar spine (Figure 5-1).

Spondylolysis usually develops in an adolescent engaged in sport activities that involve repetitious lumbar flexion and extension, such as

Transverse Process

Spinous Process

Spinous Process

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