The relationships between the degree of facet joint osteoarthritis at lower lumbar spine and ligamentum flavum thickness as well as the sacral inclination

English Keywords:Lumbar spine  Facet joint  Osteoarthritis  Ligamentum Flavum  Sacral inclination angle  CT

English Abstract:

  【Abstract】 Objectives：To investigate the relationships between the degree of facet joint osteoarthritis(FJOA) at lower lumbar spine and ligamentum flavum(LF) thickness as well as the sacral inclination. Methods: The grade of bilateral FJOA from 90 patients aged 60-80 years and suffering from low back pain and sciatica was evaluated at L3/4, L4/5 and L5/S1 levels on axial CT scan, and all cases were divided into two groups as grade Ⅰ-Ⅱ(group 1) and grade Ⅲ-Ⅳ(group 2). The thicknesss of LF in two groups were measured at their median part and compared statistically. By reviewing the image data of symmetric or asymmetric FJOA at the same level, the thickness of LF on one side was compared statistically with the contralateral side at each level. Sacral inclination angle was measured on sagittal two-dimensional CT images and divided into two groups. The thicknesss of LF and component percentage of FJOA Ⅲ-Ⅳ were compared between two groups at different sacral inclination respectively. Results: At L3/4, L4/5and L5/S1 levels, the FJOA Ⅰ-Ⅱ accounted for 60.5%, 56.1% and 68.9% respectively, while the FJOA Ⅲ-Ⅳ accounted for 39.5%, 43.9% and 31.1% respectively. In group 1, the mean thickness of LF was 3.52mm, 3.77mm, and 3.22mm for L3/4, L4/5 and L5/S1 respectively; while in group 2, the mean thickness of LF was 3.72mm, 4.01mm and 3.89mm for L3/4, L4/5 and L5/S1 respectively, which showed significant difference between the two groups at each level(P<0.05). In patients with symmetric FJOA on both sides, there was no significant side-related difference as for the LF thickness at each level(P>0.05). In patients with asymmetric FJOA on both sides, the side of FJOA Ⅲ-Ⅳ showed greater LF thickness compared with the other side of FJOA Ⅰ-Ⅱ at all three levels(P<0.05). The mean sacral inclination angle was 33.2°. The group with sacral inclination angle <33.2° had significantly thicker LF than group with sacral inclination angle ≥33.2° at L4/5 and L5/S1(P<0.05), but had no significant difference compared with L3/4 level(P>0.05). The rate of FJOA Ⅲ-Ⅳ in group with sacral inclination angle <33.2° at each level showed no difference with sacral inclination angle ≥33.2°(P>0.05). Conclusions: Asymmetric FJOA on both sides is present in lower lumbar spine. The severity of FJOA at lower lumbar spine is associated with LF thickening rather than decrease of sacral inclination angle.