OBJECT

The objective of this study was to assess, in patients with degenerative lumbar spondylolisthesis, which factors determine whether the involved disc levels were restabilized or remained unstable at the time of operation using multifactorial analysis.

METHODS

A total of 195 consecutive patients who had received laminectomy with or without fusion at our hospital between 2003 and 2007 for progressed degenerative spondylolisthesis (slip percentage > 10% at lateral flexion position) with spinal canal stenosis participated in this study. Sagittal plane unstable motion was defined according to the criteria that translatory displacement was > 4 mm (translatory hypermobility) or rotatory displacement was > 10 degrees (rotatory hypermobility). There were 52 unstable cases (including 23 translatory and 43 rotatory hypermobility cases) and 143 stable cases. Nine parameters were investigated retrospectively as candidate factors: age, sex, body mass index, disc level, grade of disc degeneration, grade of disc spur formation, facet effusion size, length of facet spur formation, and angle between facets. The differences in the candidate factors between the unstable and stable group, together with the association between translatory or rotatory displacements and factors other than sex and disc level, were investigated. Multivariate logistic regression analysis was also used to determine independent factors for the presence of unstable motion at the time of operation.

RESULTS

The unstable group had significantly greater facet effusion size (p < 0.001) than the stable group. There were no significant differences between the 2 groups in age, sex, body mass index, disc level, grade of disc degeneration, grade of disc spur formation, length of facet spur formation, or angle between facets. Multiple regression analysis for all candidate factors (except for sex and disc level) indicated that translatory displacement significantly correlated with facet effusion size positively (p < 0.001), and that rotatory displacement significantly correlated with facet effusion size positively (p < 0.001) and with age (p = -0.042) and grade of disc degeneration (p = -0.033) negatively. Logistic regression analysis for all candidate factors demonstrated that increased facet effusion size (OR 1.656, 95% CI 1.182-2.321) was the only independent factor for the presence of unstable motion at the time of operation. Facet effusion size had high negative but low positive predictive value in determining unstable motion at the time of operation. One of the reasons for the low positive predictive value was the association between facet spur formation and restabilization of the segments in the patients with greater facet effusion.

CONCLUSIONS

Facet effusion size was associated with the determination of whether the affected disc was stabilized or remained unstable at the time of operation. In particular, a smaller facet effusion size strongly suggested that the affected disc had been restabilized in the patients with lumbar degenerative spondylolisthesis.