Kinematic Characteristics and Biomechanical Changes of Lower Lumbar Facet Joints Under Different Loads.

OBJECTIVE To explore the kinematic biomechanical changes and symmetry in the left and right sides of the facet joints of lumbar spine segments under different functional loads. METHODS Participants (n = 10) performing standing flexion and extension movements were scanned using computed tomography (CT) and dual fluoroscopy imagine system. Instantaneous images of the L3 -S1 vertebrae were captured, and by matching a three-dimensional CT model with contours from dual fluoroscopy images, in vivo facet joint movements were reproduced and analyzed. Translations and rotations of lumbar vertebral (L3 and L4 ) facet joints of data were compared for different loads (0, 5, 10 kg). The participants performed flexion and extension movements in different weight-bearing states, the translations and angles changes were calculated respectively. RESULTS From standing to extension, there were no statistical differences in rotation angles for the facet joint processes of different vertebral segment levels under different weight loads (P > 0.05). Mediolateral axis and cranio-caudal translations under different weight loads were not statistically different for vertebral segment levels (P > 0.05). Anteroposterior translations for L3 (1.4 ± 0.1 mm) were greater than those for L4 (1.0 ± 0.1 mm) under the different load conditions (P = 0.04). Bilaterally, mediolateral, anteroposterior, and cranio-caudal translations of the facet joints under different weights (0, 10 kg) for each segment level (L3 and L4 ) were symmetric (P > 0.05). From flexion to standing, there were no statistical differences in rotation angles for different weights (0, 5, 10 kg) for each level (L3 and L4 ) (P > 0.05). There were no statistical differences between mediolateral, anteroposterior, and cranio-caudal translations at each segment level (L3 and L4 ) under different loads (P > 0.05). Under the condition of no weight (0 kg), L3 mediolateral translations on the left side (1.7 ± 1.6 mm) were significantly greater (P = 0.03) than those on the right side (1.6 ± 1.6 mm). Left side (1.0 ± 0.7 mm) L4 mediolateral translations were significantly smaller (P = 0.03) than those on the right side (1.1 ± 0.7 mm). There were no statistical differences between different weights for either anteroposterior and cranio-caudal translations (P > 0.05). There were no statistical differences for mediolateral, anteroposterior, and cranio-caudal translations for 10 kg (P > 0.05). CONCLUSION Lumbar spine facet joint kinematics did not change significantly with increased loads. Anteroposterior translations for L3 were greater than those for L4 of the vertebral segments are related to the coronal facet joint surface. Changes in facet surface symmetry indicates that the biomechanical pattern between facet joints may change.