Background Lumbar facet joints (LFJs) are usually related to the pathogenesis of the spine. The purpose of this paper is to study the effects of lifting load on the motion of lower lumbar facet joints in vivo. Methods Ten healthy volunteers aged 25 ≤ 39 years, 5 males and 5 females, were recruited. Using a dual fluoroscopy imaging system (DFIS) combined with CT, firstly, the L3-S1 segment image scanned by CT was converted into a three-dimensional model. Then, the lumbar motion images of L3-S1 vertebrae taken by the DFIS under different loads (0 kg, 5 kg, 10 kg) and different body postures (maximum flexion and extension, maximum left and right bending, and maximum left and right torsion) were captured. Finally, in the Rhino software, the instantaneous motion state of the lumbar spine is reproduced by translation and rotation according to the anatomical structure of the lumbar spine and the previous images. With the help of computer software, a Cartesian coordinate system was placed in the center of each articular surface to measure the kinematics of the articular process and to obtain 6DOF data under different loads (0 kg, 5 kg, 10 kg) in the lumbar facet joints.  Results In the flexion and extension of the trunk, weight bearing reduced the translational range in the mid-lateral direction. In the L3/4 segment, the lateral translational range of the left and right facet joints gradually decreased with increasing load, and the translational range at 0 kg was significantly greater than that at 10 kg (left side: 0 kg, 0.86° ± 0.57°, 10 kg, 0.24° ± 0.26°, p = 0.01; right side: 0 kg, 0.86° ± 0.59°, 10 kg, 0.26° ± 0.27°, p = 0.01). In the L5/S1 segment, the translation range of the LFJ at 0 kg was significantly greater than that at 10 kg (p = 0.02). Other bending and rotation movements were not found to cause differential changes in the 6DOF of the LFJ. In bending, the rotation range was the largest in the L3/4 segment (p < 0.05) and gradually decreased from top to bottom. At the same level, there were significant differences in the translation range of the left and right facets in the anterior posterior and craniocaudal directions (p < 0.05). Conclusion Increasing the load has a significant impact on the coupled translational movement of lumbar facet joints. The asymmetric translational movement of the left and right facet joints may be a factor that accelerates the degeneration of facet joints.

Background Quantitative data on in vivo vertebral disc deformations are critical for enhancing our understanding of spinal pathology and improving the design of surgical materials. This study investigated in vivo lumbar intervertebral disc deformations during axial rotations under different load-bearing conditions. Methods Twelve healthy subjects (7 males and 5 females) between the ages of 25 and 39 were recruited. Using a combination of a dual fluoroscopic imaging system (DFIS) and CT, the images of L3–5 segments scanned by CT were transformed into three-dimensional models, which matched the instantaneous images of the lumbar spine taken by a double fluorescent X-ray system during axial rotations to reproduce motions. Then, the kinematic data of the compression and shear deformations of the lumbar disc and the coupled bending of the vertebral body were obtained. Results Relative to the supine position, the average compression deformation caused by rotation is between + 10% and − 40%, and the shear deformation is between 17 and 50%. Under physiological weightbearing loads, different levels of lumbar discs exhibit similar deformation patterns, and the deformation patterns of left and right rotations are approximately symmetrical. The deformation patterns change significantly under a 10 kg load, with the exception of the L3–4 disc during the right rotation. Conclusion The deformation of the lumbar disc was direction-specific and level-specific during axial rotations and was affected by extra weight. These data can provide new insights into the biomechanics of the lumbar spine and optimize the parameters of artificial lumbar spine devices.

Background: Orientation of the lumbar facet joints (FJs) in the transverse plane is associated with degenerative lumbar spine disease. However, there is a lack of measurements of the sagittal and coronal facet angles, and the effect of 3D facet angles on joint motion in the sitting position is unknown. The present study was to investigate the 3D orientation and in vivo motion characteristics of the FJ in the sitting position.Methods: Dual fluoroscopic imaging system and computed tomography (CT) were used to determine the 3D orientation and kinematic characteristics of FJs. L3-S1 segments were studied in 10 asymptomatic participants (5 male and 5 female, age: 25-35 years, body mass index: 22.4±1.8). Angles of the facet in the sagittal, coronal, and axial planes, and the range of motion of the FJs in seated flexion and extension movements were measured. Results:The difference in sagittal facet angles between the 2 sides of the L3-S1 facet joints was not significant. The superior coronal facet angle on the left side of L5 was significantly smaller than that on the right side by 6.4° (P=0.01). The inferior transverse facet angle on the left side of L5 was greater than that on the right side by 7.1; the results were not statistically significantly different. In the sitting position, the range of motion of the left and right sides of L5-S1 differed significantly, with the right side being 5.5° (P=0.004) and 11.7° (P=0.026) greater than the left side in the sagittal and coronal planes, respectively. There was a correlation between mobility and the 3D orientation angle of the FJs in each segment.Conclusions: Quantification of the 3D orientation of the lumbar spine FJs provides new perspectives to study the kinematics of the lumbar spine and the etiology of lumbar degenerative diseases. In sitting flexion and extension movements, there is a significant difference in the left-right lateral mobility of the FJs of the L5-S1 segments. With the exception of the transverse facet angle of the lumbar spine FJs, the sagittal and coronal facet angles also have an effect on lumbar spine mobility.

Background Lumbar Intervertebral Disc Degeneration (LDD) is one of the largest health worldwide problems, based on lost working time and associated costs. Inappropriate mechanical loading is considered to be an important factor in the development of LDD. L3-4 and L4-L5 were the commonly affected levels. Recent studies have measured geometric deformation of lumbar intervertebral discs during an in vivo functional weightbearing of the lumbar. The purpose of the present study was to determine the lumbar disc deformation in living human subjects during lateral bending motion under different load-bearing conditions. Methods 11 healthy subjects, 6 males and 5 females, aged 21 ≤ 39 years, with an average age of 30 ± 5 years, were recruited for the present study. Using the combination of dual fluoroscopic imaging system(DFIS)and CT, the sagittal images of L3-5 segments scanned by CT were transformed into three-dimensional reconstruction models and then matched to the instantaneous images of lumbar spine motion taken by a double fluorescent X-ray system under different loads. Motions were reproduced with the use of the combined imaging technique during left and right bending movements. Then, the kinematics data of the height, tension and compression deformation, and shear deformation of the lumbar intervertebral disc were obtained by using computer-related software. Result The data indicated that the tendency of tensile deformation during left and right bending was approximately symmetric. During the functional bending of the body, there was a greater compression deformation behind the same side of the movement and a higher tension deformation in front of the contralateral movement. The magnitude changed along the diagonal towards the posterolateral direction. During left bending, the upper vertebrae had a larger deformation range and tension deformation than the lower vertebrae. Meanwhile, it was not found that the small load had a significant effect on the tensile deformation of the intervertebral disc. Conclusion Lumbar disc deformation showed direction-specific and level-specific changes during lateral bending motion. These results could help understand the physiological motion characters of the lumbar spine and provide data support for other biomechanical studies.