The Effects of Orientation of Lumbar Facet Joints on the Facet Joint Contact Forces: An In Vitro Biomechanical Study

Abstract

Study design: A biomechanical human cadaveric study.

Objective: The aim of this study was to measure L2-L3 facet joint contact forces in a flexibility test using thin film electroresistive sensors, and facet joint orientation on computed tomographic (CT) scan images, to examine the effects of orientation of lumbar facet joint on the facet joint contact forces.

Summary of background data: Biomechanically, the bilateral facet joints play a critical role in maintaining stability of the lumbar spine. The effect of orientation of lumbar facet joints on the contact forces remains unknown.

Methods: Eight human cadaveric lumbar spine specimens (L2-L3) were tested by applying a pure moment of ±7.5 Nm in three directions of loading (flexion-extension, lateral bending, and axial rotation) with and without a follower preload of 300 N. The orientation of the lumbar facet joints at the L2-L3 was measured on axial CT scans. Bilateral facet contact forces were measured during flexibility tests using thin film electroresistive sensors (Tekscan 6900).

Results: The average total peak facet loads was 66 N in axial rotation, 27 N in extension, and 20 N in lateral bending under a pure moment. Under a pure moment with a follower preload of 300 N, the average total peak facet loads was 53 N in axial rotation, 43 N in extension, and 24 N in lateral bending. The facet joint forces were correlated positively and significantly with the orientation in all directions with and without a compressive follower preload (P < 0.05). In addition, the facet joint contact forces at neutral position with a follower preload were correlated positively with the orientation (rs = 0.759, P = 0.001).

Conclusion: This study identified that the greater coronal orientation of lumbar facet joints is, the higher the facet joint contact forces are.

Level of evidence: 3.