Lamina horizontalization and facet tropism as the risk factors for adjacent segment degeneration after PLIF.

Study Design. A retrospective case-control study. Objective. To clarify associations between both lamina horizontalization and facet tropism and adjacent segment degeneration (ASD). of Background Data. We have previously reported coexistence of lamina horizontalization and facet tropism adjacent to the cranial fusion segment as risk factors for ASD. Methods. Subjects comprised 20 patients who underwent additional surgery for ASD after L4/5 posterior lumbar interbody fusion (PLIF) for L4 degenerative spondylolisthesis. Patients who underwent additional surgery for ASD (ASD group) were divided into 2 groups according to the duration until additional surgery: early group (n = 13), additional surgery ≤3 years after primary surgery; and late group (n = 7), additional surgery >3 years after primary surgery. As a control group, 20 age- and sex-matched patients who underwent L4/5 PLIF and could be followed for ≥5 years without ASD were selected. Lamina inclination angle at L3 and facet tropism at L3/4 in each group were measured 3 times by 3 individuals blinded to clinical results. Associations between clinical results and these risk factors and influences of these factors for periods up to the occurrence of ASD were investigated. Results. All ASD was observed in the cranial adjacent segment and the most common condition at additional surgery was spondylolisthesis (n = 15, 75%). Lamina inclination angle was significantly higher in the ASD group than in the control group. ASD was observed in 86% of patients with lamina inclination >130°. In addition, facet tropism was more significant in the early group than in the late and control groups. ASD was observed ≤3 years after primary surgery in all patients with both lamina inclination >130° and facet tropism >10°. Conclusion. Preexisting lamina horizontalization at the cranial fusion segment seems to affect ASD, and coexistence of lamina horizontalization and facet tropism seems to accelerate ASD after PLIF.