In vivo measurement of lumbar facet joint area in asymptomatic and chronic low back pain subjects

Abstract

Study design: In vivo measurement of lumbar facet joint surface area.

Objective: To investigate lumbar facet joint surface area in relation to age and the presence of chronic low back pain.

Summary of background data: Facet joint surface area is an important parameter for understanding facet joint function and pathology, but information on the lumbar facet joint is limited, especially in relation with age and low back pain symptoms.

Methods: In vivo measurements of the lumbar facet joints (L3/L4-L5/S1) were performed on 90 volunteers (57 asymptomatic subjects and 33 chronic low back pain subjects) using subject-based 3-dimensional facet joint surface computed tomography models.

Results: The facet joint surface area increased significantly at each successive inferior level. In the low back pain subjects aged >40 years, both superior and inferior facet surface areas increased except superior facets at L5/S1 compared with younger subjects. In the asymptomatic subjects aged >40 years, only the superior facets showed an increase in the L3/4 facet surface area compared with younger subjects.

Conclusion: The lumbar facet areas measured in vivo in this study were similar to previous cadaveric studies. The lumbar facet area was significantly greater at the inferior lumbar levels and also increased with age. This age-related increase in the facet joint surface was observed more in the low back pain subjects compared with asymptomatic subjects. The increase in the area of the facet joint surface is probably secondary to increased load-bearing in the lower lumbar segments and facet joint osteoarthritis.

Figure 1

Fifteen equidistant points were generated on the joint surface line traced in each slice. Polygons were created by using 2 adjacent points in one plane (j or j+1) and 1 point in the adjacent plane (j +1 or j). For example, an arbitrarily triangle was consisted by K_th point in plane j, K_th point in plane j+1, and (K+1)_th point in plane j+1. The area of each polygon was computed by calculating the cross product of the 2 vectors, A and B. A normal vector of the polygon, N, was obtained simultaneously by the cross product of the 2 vectors (the normal vector was not analyzed in the current study). Therefore, the entire facet joint surface was modeled with the resulting polygon elements.

Figure 2

The 3D surface model of the facet joint consisting of polygons. Distribution of the normal vectors (green lines) indicates 3D curvature of the facet joint surface. The area of the entire facet joint surface was calculated by summating the area of the polygons throughout the three-dimensionally curved joint surface.

Figure 3

Facet joint surface areas (mm²) (mean±SEM) of superior and inferior facets at left or right side for L3/L4-L5/S1.