Spondylolisthesis, or displacement of one vertebra on another, often occurs in association with spondylolysis.
Stress fracture of the neural arch of the vertebra (spondylolysis) is observed most frequently in the lumbar spine, especially the fifth lumbar vertebra. The patient may be asymptomatic, although back and radicular pain, tenderness, gait abnormality and neurologic deficits can be observed. In general, 3 7% of vertebral columns reveal at least one area of spondylolysis, but the frequency appears to be greater in athletes and in male subjects. In almost all cases spondylolysis represents a stress fracture. Rarely, a single traumatic episode can result in spondylolysis. Lumbar spondylolysis can be classified into five types (Table 1).
Spondylolysis, Table 1. Classification of spondylolysis.
| Type I: | Dysplastic, with associated congenital abnormality of the upper sacrum and the arch of the lumbar vertebra |
| Type II: | Isthmic, with a defect in the pars interarticularis that may be (1) a fatigue fracture, (2) an elongated but intact pars, or (3) an acute fracture |
| Type III: | Degenerative, resulting from long-standing intersegmental instability |
| Type IV: | Traumatic, caused by fractures in areas of the posterior elements other than the pars interarticularis |
| Type V: | Pathologic, due to generalized or localized bone disease |
Spondylolysis is usually evident on lateral radiographs, but oblique views are particularly helpful (Fig.1). Hypertrophy and reactive sclerosis as well as fracture of the contralateral pedicle and lamina may be detected as a physiologic response to the presence of an unstable neural arch. Scintigraphy may allow the detection of more recently acquired and symptomatic spondylolyses, as such defects will accumulate the bone-seeking radiotracer. CT scanning has also been used to delineate areas of spondylolysis as well as other clefts in the neural arch that are rarer than those in the pars interarticularis. The role of MR imaging in the diagnosis of spondylolysis appears to be limited.
Spondylolysis also occurs in many patients with Marfans syndrome and Ehlers Danlos syndrome. In the latter disease it may be severe.
