Progression of spondylolysis to isthmic spondylolisthesis in an adult without accompanying disc degeneration: a case report.

Progression of spondylolysis to spondylolisthesis in adults is very rare. It is always accompanied by disc degeneration at the slip level, or at a lower level. The intervertebral disc is indeed the main structure that opposes the anteriorly directed shear forces. Of course, the disc degeneration might also be a consequence, rather than a cause of the slip. The authors describe an unusual case of progression of spondylolysis to spondylolisthesis in an adult, without any disc degeneration. They are not aware of a similar case in the literature. In 1999, an aircraft engineer with known asymptomatic spondylolysis was involved in a low impact motorcycle accident, after which a Grade I spondylolisthesis L4 was diagnosed. There was no predisposing disc space narrowing at any vertebral level. There may have been a certain degree of microscopic disc degeneration L4L5, a possibility which was confirmed by the development of a disc hernia L4L5, seven years after trauma. This case illustrates the potential for progression of spondylolysis to spondylolisthesis in an adult, without radiographical signs of disc degeneration at any level. The minimal trauma might have played a role. The authors recommend that patients with known spondylolysis who sustain acute exacerbation of their back pain should have standing radiographs.