Spondylolysis and isthmic spondylolisthesis: impact of vertebral hypoplasia on the use of the Meyerding classification

Abstract

Background: Spondylolysis and isthmic spondylolisthesis are common multifactorial disorders. The extent of slipping of the spondylolytic vertebra is considered a major predicator for prognosis and further follow-up. Vertebral hypoplasia is a common finding associated with spondylolysis. The purpose of this study is to evaluate the incidence of hypoplastic vertebral bodies in patients with spondylolysis and in the general population and to analyse the impact of the findings on the measurement and grading of spondylolisthesis.

Methods: 140 patients with 141 levels of spondylolysis identified by MRI were included in this study. The slippage of the spondylolytic vertebral body and the size in the midline sagittal image were measured and correlated. In addition, a randomised control group was evaluated to test the hypothesis that shortened, hypoplastic vertebral bodies can also be found in the general population.

Results: Shortened, hypoplastic vertebrae were found in 50 patients with spondylolysis and none was found in the control group. These shortened vertebrae mimicked spondylolisthesis and in 19 patients the slippage equalled the shortening, thus mimicking spondylolisthesis, although only spondylolysis was present.

Conclusion: Sagittal shortening of the spondylolytic vertebra is common and may mimic spondylolisthesis. In order to define and measure spondylolisthesis the shortening of the spondylolytic vertebra has to be taken into account.

Figure 1

Measurement of slippage of the spondylolytic vertebra L5 over S1 is shown in a sagittal midline T₂ weighted scan of the lumbar spine. A similar section is shown with and without the measurements. First line, A, is drawn, which connects the dorsal edges of L5 to each other. Then the upper margin of S1 is pointed to the computer, which draws a parallel line to the first line, B. The connecting line, C, is equal to the slip. The value of this line is recorded in millimetres. L, lumbar; S, sacral.

Figure 2

Measurement of the difference in size between the spondylolytic vertebra L5 and S1 is shown in a sagittal midline T₂ weighted scan of the lumbar spine. A similar section is shown with and without the measurements. Two lines from the measurement in Figure 1 are in light grey to show the measured slip of L5 over S1. Line A shows the measurement of the length of L5 at the lower margin. Line B depicts the measurement of the upper margin of S1. Both values are noted in millimetres and the difference in size, showing the shortening of L5, is recorded. L, lumbar; S, sacral.

Figure 3

Measurement of the difference in size between L5 and S1 is shown in a sagittal midline T₂ weighted scan of the lumbar spine of a patient from the control group. A similar section is shown with and without the measurements. Line A shows the measurement of the length of L5 at the lower margin. Line B depicts the measurement of the upper margin of S1. Both values are noted in millimetres and the difference in size is recorded. L, lumbar; S, sacral.