Background:

The pedicle screw is the most common device used to achieve fixation in fusion of spondylolistheses. Safe and accurate placement with this technique relies on a thorough understanding of the bony anatomy. There is a paucity of literature comparing the surgically relevant osseous anatomy in patients with a degenerative spondylolisthesis (DS) and an isthmic spondylolisthesis (IS). The goal of this study was to determine the differences in the osseous anatomy in patients with a DS and those with an IS.

Methods:

A retrospective comparative cohort study was conducted on patients with a single-level, symptomatic L4-L5 DS or a single-level, symptomatic L5-S1 IS. Magnetic resonance imaging for these patients was reviewed. Morphometries of the pedicle and vertebral body were analyzed by 2 independent observers for the levels from L3 to S1, and radiographic parameters were compared between groups.

Results:

A total of 572 levels in 143 patients were studied, including 103 patients with a DS and 40 with an IS. After accounting for confounders, IS and DS had an independent effect on transverse vertebral body width, pedicle height and width, and sagittal pedicle angle. Patients with an IS had a smaller pedicle height (P < .001) and pedicle width (P = .001) than patients with DS. In addition, the angulation of the pedicles varied on the basis of the diagnosis.

Conclusions:

The osseous anatomy is significantly different in patients with a DS than with an IS. Patients with an IS have smaller pedicles in the lumbar spine. Also, the L4 and L5 pedicles are more caudally angulated and the S1 pedicle is less medialized.

Level of evidence:

3.

Clinical relevance:

Understanding the differences in pedicle anatomy is important for the safe placement of pedicle screws.