Objective To evaluate the biomechanical effect of a self-made iliac screw plate on the stability of lumbo-iliac fixation construct before and after fatigue loading. Methods Twelve fresh lumbo-pelvic specimens from donated adult cadavers with formalin embalm were used in the study. According to whether use the iliac screw plate or not, the specimens were randomly assigned into group A (with iliac screw plate, n=6) and group B (without iliac screw plate, n=6). The bone mineral density (BMD) of L1-4 was measured using dual-energy radiograph absorptiometry. The pedicle screw and iliac screw fixation were given at L3-5, and bilateral facetectomy and diskectomy at L5, S1 level were performed to prepare the model of the intervertebral destabilization. The biomechanical testing was conducted on a material testing machine under 0-600 N compression and — 7-7 N · m torsion loading modes for the initial compressive stiffness and torsional stiffness evaluation. And then 20 000 cyclic compressive loading of 40-400 N was given to the specimen, the stiffness evaluation was repeated. Then the maximum pull-out strength of screws at every level was measured and compared. Gross observation and radiological observation were performed during experiment. Results The BMD values of groups A and B were (1.15 ± 0.13) g/cm2 and (1.12 ± 0.11) g/ cm2 respectively, showing no significant difference between 2 groups (t=0.428, P=0.678). All pedicle screws and iliac screws were inserted in good position; no loosening or breaking of screw was observed during loading. After fatigue loading, the incidence of halo ring around the iliac screws of groups A and B was 16.7% (1/6) and 50.0% (3/6), respectively. The compressive stiffness and torsional stiffness after fatigue loading were significantly lower than those in initial state in groups A and B (P lt; 0.05); there was no significant difference in compressive stiffness and torsional stiffness between groups A and B before fatigue loading (P gt; 0.05). However, group A had higher compressive stiffness than group B (t=2.664, P=0.024) after fatigue loading, and there was no significant difference in torsional stiffness between 2 groups (t=0.410, P=0.690). No significant difference was found in screw pull-out strength of pedicle screws at L3, L4, and L5 levels between groups A and B (P gt; 0.05); however, the pull-out strength of the iliac screws in group A was significantly higher than that in group B (t=3.398, P=0.007). In groups A and B, the pull-out strength of L3 screw was significantly lower than that of L4 and L5 screws (P lt; 0.05). In group A, pull-out strength of the iliac screws was significantly higher than that of L3, L4, and L5 screws (P lt; 0.05); in group B, the pull-out strength of iliac screws was significantly lower than that of L4 and L5 screws (P lt; 0.05). Conclusion In the lumbo-iliac reconstruction, the use of iliac screw plate could resist iliac screw loosening, therefore, it has the potential to increase the stability of lumbo-iliac fixation construct.
Objective To observe the systemic and local immune response after repair of nerve defect with acellular nerve xenograft laden with allogenic adipose-derived stem cells (ADSCs) in rhesus monkey so as to evaluate the safety of the proposed material for nerve reconstruction. Methods Bilateral tibial nerves were taken from a healthy adult male landrace (weighing 48 kg) to prepare acellular nerve xenograft by chemical extraction. ADSCs were isolated from a healthy adult male rhesus monkey (weighing 4.5 kg), and were seeded into the acellular nerve grafts. The radial nerve defect models with 25 mm in length were established in 10 healthy adult female rhesus monkeys (weighing 3-5 kg), and they were divided into cell-laden group (n=5) and non-cell-laden group (n=5) randomly. Defect was repaired with acellular nerve xenograft laden with allogenic ADSCs in cell-laden group, with acellular nerve xenograft only in non-cell-laden group. The blood samples were taken from peripheral vein preoperatively and at 14, 60, and 90 days after operation for lymphocyte analysis; at 5 months after operation, the grafts were harvested to perform histological examination for local immune response and nerve regeneration. The nerve autograft in rhesus monkey was used as control. Results In cell-laden group and non-cell-laden group, no significant difference was found in the count of lymphocytes and T lymphocytes, the percentage of T lymphocytes, CD8+ T lymphocytes, as well as the ratio of CD4+ T lymphocytes to CD8+ T lymphocytes between pre- and post-operation (P gt; 0.05); in cell-laden group, the percentage of CD4+ T lymphocytes at 14 days was significantly lower than that at 60 and 90 days postoperatively (P lt; 0.05). The percentage of CD4+ T lymphocytes in cell-laden group was significantly lower than that in non-cell-laden group at 14 days (P lt; 0.05), but no significant difference was found in the other indexes at the other time between 2 groups (P gt; 0.05). At 5 months after operation, mild adhesion was found on the surface of nerve xenografts; the epineurium of nerve xenografts was thicker than that of nerve autografts; and neither necrosis nor fibrosis was found. CD3+, CD4+, CD8+, CD68+, and CD163+ T lymphocytes were scattered within the grafts, in which regenerative axons were revealed. CD3+, CD4+, CD8+, CD68+, and CD163+ T lymphocytes were comparable in cell-laden group, non-cell-laden group, and autograft group. Conclusion Repair of nerve defect with acellular nerve xenograft elicits neither systemic nor local immune response in rhesus monkeys. Implantation of allogenic ADSCs might result in transient depression of CD4+ T lymphocytes proliferation early after surgery, no immune response can be found.