Accelerated sagittal remodeling of lumbar facet joints following L4-L5 posterior lumbar interbody fusion: a longitudinal MRI study

This study aimed to investigate whether the progression of lumbar facet joint angle (FJA) in adjacent segment degeneration (ASD) occurs more rapidly in the sagittal plane compared to a matched control group.

This retrospective longitudinal study included 35 individuals from three hospitals who underwent L4-L5 posterior lumbar interbody fusion (PLIF) surgery and had preoperative lumbar magnetic resonance imaging (MRI) scans. These patients also underwent follow-up MRI scans approximately four to five years postoperatively. A control group, matched for age and gender, was included for comparative analysis. MRI data were assessed using grading scales for facet joint degeneration (FJD) and lumbar intervertebral disc degeneration (IDD). FJA measurements were derived from T2-weighted axial images.

No significant progression of IDD was found in either group. Within the PLIF group, a more rapid progression of FJD was observed at the bilateral L5-S1 and right L3-L4 segments in comparison to the control group (P < 0.05). In contrast, the control group exhibited consistent lumbar FJA across all segments. Postoperative MRI scans of the PLIF group, however, demonstrated a significant reduction in FJA on both sides of the L3-L4 segment and on the left side of the L5-S1 segment (P < 0.05), with no significant changes observed at the L2-L3 segment and the right side of the L5-S1 segment. A significant negative correlation was found between the change in FJA (ΔFJA) and the change in FJD (ΔFJD) at the left L5–S1 segment in the PLIF group (ρ = −0.335, P = 0.049).

Accelerated sagittal facet remodeling occurs at segments adjacent to L4–L5 PLIF and correlates with facet degeneration. These hypothesis-generating preliminary findings suggest that FJA measurement has the potential to serve as an imaging biomarker for ASD risk, though this interpretation remains to be validated in larger prospective cohorts. The findings underscore the need for long-term postoperative surveillance.