Background Advancements in medicine and the popularity of lumbar fusion surgery have made lumbar adjacent segment disease (ASDz) increasingly common, but there is no mature plan for guiding its surgical treatment. Therefore, in this study, four different finite element (FE) ASDz models were designed and their biomechanical characteristics were analysed to provide a theoretical basis for clinical workers to choose the most appropriate revision scheme for ASDz. Methods According to whether internal fixation was retained, different FE models were created to simulate ASDz revision surgery, and flexion, extension, axial rotation and lateral bending were simulated by loading. The biomechanical characteristics of the adjacent segments of the intervertebral disc and the internal fixation system and the range of motion (ROM) of the lumbar vertebrae were analysed. Results The difference in the ROM of the fixed segment between FE models that did or did not retain the original internal fixation was less than 0.1°, and the difference was not significant. However, the stress of the screw–rod system when the original internal fixation was retained and prolonged fixation was performed with dual-trajectory screws was less than that when the original internal fixation was removed and prolonged fixation was performed with a long bar. Especially in axial rotation, the difference between models A and B is the largest, and the difference in peak stress reached 30 MPa. However, for the ASDz revision surgery segment, the endplate stress between the two models was the lowest, and the intradiscal pressure (IDP) of the adjacent segment was not significantly different between different models. Conclusion Although ASDz revision surgery by retaining the original internal fixation and prolonging fixation with dual-trajectory screws led to an increase in stress in the fusion segment endplate, it provides stability similar to ASDz revision surgery by removing the original internal fixation and prolonging fixation with a long bar and does not lead to a significant change in the IDP of the adjacent segment while avoiding a greater risk of rod fracture.

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.

Objective To investigate and evaluate the biomechanical behaviour of tension-band-reconstruction (TBR) and ordinary titanium plates in open-door laminoplasty by finite element (FE) analysis. Methods TBR titanium plate and ordinary titanium plate were implanted into a validated finite element model of healthy adult cervical vertebrae. Among them, 5 ordinary titanium plate were used in model A, 2 TBR titanium plates and 3 ordinary titanium plates were used in model B, and 5 TBR titanium plates were used in model C. The same loading conditions was applied identically to all models. Range of motion (ROM) of the vertebral body, stress distribution of the titanium plate and intradiscal pressure (IDP) were compared in flexion, extension, lateral bending and rotation. Results The ROM of model B and C was similar in flexion and extension, and both were smaller than that of model A. The highest von Mises stress in the titanium plate appears is in model C. The IDP in C2/3 was significantly higher than that in other segments in flexion. There was no significant difference in IDP among three models in left lateral bending and left axial rotation. Conclusion Application of TBR titanium plate in open-door laminoplasty can reduced ROM in flexion, extension and axial rotation of the cervical vertebrae. But the increase of stress in TBR titanium plate could lead to higher risk of adverse events such as titanium plate deformation. Moreover, compared with complete TBR titanium plate, the combination of TBR titanium plate for C3 and C7 with ordinary titanium plate for the other vertebrae largely reduce the stress of the titanium plates by ensuring stability. The proposed FE model (C2-T1) exhibits a great potential in evaluating biomechanical behaviour of TBR titanium plate for open-door laminoplasty.

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.