Introduction: Facet joints possess a critical role in resisting anterior shear forces. A more sagittal facet joint was proposed to be associated with lumbar degenerative spondylolisthesis (DS) in many researches. However, whether the sagittal positioning of facet joints works as a preexisting morphological factor or result from remodeling after spondylolisthesis occurs remains controversial. Our study aimed to evaluate the causal relationship between spondylolisthesis and facet angles of L2-S1 facet joints in patients with double-level degenerative spondylolisthesis (double-DS).
Methods: Forty-two patients with L3-L5 double-DS and one hundred and seven patients with single-level L4/5 DS (single-DS) who had undergone surgical intervention from September 2016 to September 2021were included. Besides, 100 age- and sex- matched healthy participants were involved as control. Facet joint angles at each level from L2-S1 were measured on preoperative CT images. The slippage parameters and spino-pelvic parameters of DS groups were also measured on lateral full-spine X-ray image.
Results: Double-DS group had an average age of 64.42 ± 6.20 years, and single-DS group had an average age of 63.59 ± 6.08 years. Both the right and left facet angles of L2-S1segments in spondylolisthesis patients were larger than healthy control group (all P < 0.05). In spondylolisthesis patients, double-DS facet angles of L2/L3 level (no spondylolisthesis in double-DS or single-DS group) and L3/L4 levels (no spondylolisthesis in single-DS but spondylolisthesis in double-DS) were significantly sagittalized (P < 0.05) compared with single-DS, while those of L4/L5 level (spondylolisthesis levels in both double-DS and single-DS groups) and L5/S1 level (no spondylolisthesis in either group) showed no differences (P > 0.05). As for X-ray parameters. PI, TK, L4/5 slippage distance and L4/5 slippage percentage showed no difference between double-DS and single-DS groups. The PT, SVA, L3 slope and L4 slope of double-DS were greater (P < 0.05) while the SS, LL, L3-L4 disc height, L4-L5 disc height, L4-L5 slippage angle and L3-S1 height were smaller compared with single-DS groups. Of note, facet tropism (>8°) was more frequently seen in spondylolisthesis segments than non-spondylolisthesis segments (P < 0.05).
Discussion: In addition to abnormalities of the intervertebral discs, the changes in the facet joint angles have long been regarded in literature as the risk factors of DS. In our research, significantly sagittalized facet joints in all levels of DS groups compared with healthy control group indicated that before spondylolisthesis happened, facet joint angulation difference already existed. Also, more sagittalized facet joints of double-DS L2/L3 level compared with single-DS support this conclusion. Yet in L3/L4 level, double-DS groups with spondylolisthesis segments had larger facet joints angles than non-spondylolisthesis segments of single-DS. On this basis, it appears to further evidence that facet joints are remodeled with the development of spondylolisthesis. Taking together, we draw the conclusion that facet joint angulation exists before spondylolisthesis, and spondylolisthesis aggravates its progression.