ABSTRACT
Objective To analyze the biomechanical characteristics of lumbar fusion by 3 internal fixation methods using three-dimensional (3D) finite element (FE) method. Methods The FE fixation models of physiological L4-5, unfixed fusion L4-5, translaminar facet screw (TLFS), lumbar pedical screw+translaminar facet screw (LPS+TLFS), bilateral pedical screw (BPS) with complete osteotomy or partial osteotomy of facet joint were established, respectively. The biomechanical characteristics of L4 centrum and implants under six motion states (spinal flexion, extension, lateral bending and axial rotation) in L4-5 fusion model and three fixation models were compared by FE analysis. Results The average maximal displacements of L4 centrum in L4-5 unfixed fusion model, TLFS model, TLFS+LPS model, BPS model were 1.410 8, 0.629 8, 0.336 9, 0.252 8 mm (complete osteotomy of facet joint) and 1.296 7, 0.844 9, 0.340 9, 0.273 8 mm (partial osteotomy of facet joint); the average maximal displacements of cage were 0.479 9, 0.319 5, 0.167 6, 0.126 4 mm (complete osteotomy of facet joint) and 0.378 7, 0.348 4, 0.183 5, 0.137 2 mm (partial osteotomy of facet joint)；the average maximum stresses of screws and rods during 6 motions in TLFS model, TLFS+LPS model, BPS model were 178.34, 79.55, 56.33 MPa (complete osteotomy of facet joint) and 142.29, 103.02, 59.69 MPa (partial osteotomy of facet joint). Conclusions In percutaneous transforaminal lumbar interbody fusion, the fixation effect of BPS model was similar to that of LPS+TLFS model. BPS model could achieve the best spinal stability, and LPS+TLFS model was also a good fixation method. The stability of TLFS model alone was relatively poor, but it was still better than that of cage bone graft without internal fixation. In the absence of internal fixation, preservation of the articular process significantly increased stability of the spine.
ABSTRACT
BACKGROUND: Bone cement coated by different materials has various characteristics and causes varying therapeutic effects. OBJECTIVE: By comparing characteristics of CPC, CPC/D, and CPC/M/D3 to investigate the preparation of doxorubicin microspheres-coated bone cement. METHODS: Doxorubicin microspheres were prepared with multiple emulsion solvent volatilixation method. Doxorubicin microspheres were mixed with CPC as the ratio of 3:7 to prepare doxorubicin microspheres-coated bone cement. The samples were randomly divided into three groups: CPC group, containing bone cement alone; CPC/D group, containing doxorubicin;CPC/M/D group, containing doxorubicin microspheres. Scanning electron microscope at varying magnification was used to observe structural characteristics and measure the diameter of microspheres. X-ray diffraction was used to estimate the extent of CPC and CPC/M/D samples. The initial and final setting time of cement samples in the three different groups was measured at 25 ℃ and 37℃ respectively. The injectability and interval porosity of different samples were tested. The compressive strength of the specimens was measured using a universal material testing machine to record the maximal compressive strength and breaking strength. RESULTS AND CONCLUSION: PLGA microspheres (100-150 μm) were globular and the surface was slick and sly. Micrestructure of bone cement was not obviously changed following mixing with drugs, thus the location and characteristics of drugs in bone cement were not determined. Micrespheres-coated bone cement (100-150 μm) was distributed among CPC powder. All the X-ray diffraction pattern of three different samples was in coincidence with standard X-ray diffraction pattern of hydroxyapatite, i.e., the major peak was located near 32°. Additional drugs and microspheres did not cause new phases. Obvious collapsing was not observed in the three samples following immediately adding in saline, but the collapsing appeared in both CPC/D and CPC/M/D samples after 24 hours. The setting-up time of CPC/M/D was the longest, but that of CPC was the shortest. On the other hand, the setting-up time was the longest at 37℃. The final setting-up time of CPC/M/D group was 45 minutes. The doxorubicin microspheres-coated bone cement showed the best property of injectability among the three kinds of cement. The interval porosity was the highest in the CPC/M/D group but the lowest in the CPC group. Interval porosity of doxorubicin microspheres-coated bone cement was up to 61.67%. The yield stress was the strongest in the CPC group but the weakest in the CPC/M/D group. Additionally, the yield stress of calcium phosphate cement dramatically decreased while doxrorubicin microspheres were coated. However, there was no significant difference between them. The preparation of doxorubicin microspheres-coated bone cement was reliable and the product had good structures and properties.