The Hidden Angles: Predictive Indices of Degenerative Spondylolisthesis at L4-5.

Objective: To examine the relationship between facet joint orientation, alignment, degeneration, and degenerative spondylolisthesis (DS) at lumbar vertebra L4-5.

Methods: A retrospective study of 114 DS patients and 114 non-DS patients admitted to our hospital from May 2019 to April 2024. We compared facet joint angle (FJA), FJA difference, FJA asymmetry, L4 inclination angle (L4IA), Weishaupt classification, paraspinal muscle cross-sectional area (CSA), pedicle-facet angle (P-F angle), and P-F angle asymmetry between the two groups. We also analyzed FJA and slippage index changes across Weishaupt grades and their correlation using Pearson correlation. The predictive value of facet joint direction indices for DS at L4-5 was assessed using ROC curves.

Results: The DS group showed reduced FJA and FJA difference, increased left asymmetry, higher L4IA levels, and a greater proportion of grade II and III in Weishaupt classification compared to the non-DS group (P<0.05). FJA decreased while the slippage index increased with more degeneration (P<0.05). Weishaupt classification was negatively correlated with FJA (r=-0.823, P<0.001), but positively with the slippage index (r=0.756, P<0.001). The P-F angle was significantly higher in the DS group (P<0.05). Cut-off values for FJA, L4IA, and P-F angle were 42.57, 9.63, and 122.17, with AUC values of 0.893, 0.766, and 0.858, respectively, indicating predictive value for DS at L4-5.

Conclusion: The DS group had smaller FJA, larger L4IA and P-F angle, and more severe facet joint degeneration at L4-5, suggesting a strong link between DS at L4-5 and facet joint sagittalization, levelization, and degeneration.