A clival-cervical plate fixation for the craniovertebral instability: a biomechanical study / 中华骨科杂志

Objective:To develop a specialized clival-cervical plate fixation (CCPF) for anterior surgery to treat craniovertebral instability, and to compare it with a posterior occipitocervical fixation (POCF) in biomechanical validation.Methods:Based on the measurement of 40 adult dry bones and 30 volunteers CT images, the clival-cervical plate was designed and manufactured. 8 cadaveric specimens (occiput-C 3) were tested in five conditions including the intact status, the intact+CCPF status, the injury status, the injury+CCPF status, and the injury+POCF status. Specimens were applied a pure moment of 1.5 N·m in flexion, extension, lateral bending, and axial rotation. Calculating and comparing the range of motion (ROM) and neutral zone (NZ) for the occiput to C 2. The effects of different fixation methods on the distribution of ROMs at the occipitocervical region were compared. Results:The injury+CCPF status constrained ROMs to 1.7° in flexion ( q=4.68, P=0.055) , 1.2° in extension ( q=0.39, P=0.9922) , 2.8° in lateral bending ( q=1.25, P=0.814) , and 4.3° in axial rotation ( q=5.08, P=0.035) , resulted in larger ROM in axial rotation but similar ROMs in other directions ( P>0.05) when compared with the injury+POCF status. There were no significant differences between the above two fixation methods in flexion-extension ( q=1.94, P=0.554) , lateral bending ( q=1.79, P=0.611) and axial rotation ( q=2.14, P=0.478) for the NZs. For the flexion, extension,lateral bendingand axial rotation direction, the proportion of the C 1, 2 ROM to the overall ROM was 28%, 25%, 34% and 56% respectively in the injury+CCPF status, and it was 59%, 53%, 42% and 71% respectively in the injury+POCF status. Conclusion:CCPF is a biomechanically effective alternative or supplemental method of POCF for the craniocervical instability.

Biomechanical Study of Posterior Dynamic Fixation at Atlantoaxial Joints / 医用生物力学

Objective To evaluate the influence of dynamic fixation (rotating and sliding pedicle screws) on stability of the atlantoaxial joint. Methods A series of in vitro biomechanical tests were performed using six fresh adult cervical spines (occipital bone-C4 segment) to simulate different conditions in surgery， including the intact state, the injury state, rigid fixation, rotating pedicle screw fixation, sliding pedicle screw fixation. The repeated measurement design was employed, and under intact, injury and different fixation states, the pure moment of 1.5 N·m in flexion-extension, left-right lateral bending, left-right axial rotation directions were applied using the spinal testing machine. The movement of atlantoaxial spine was measured consecutively by three-dimensional （3D） measurement system in order to analyze the range of motion (ROM) and neutral zone (NZ) of atlantoaxial joints. Results Under injury state, ROM of atlantoaxial joints was significantly larger than that under intact state during flexion, extension, lateral bending and rotation, leading to the instability of atlantoaxial joints. ROM of fixation segments was significantly reduced during flexion, extension, lateral bending and rotation after rigid and dynamic fixation. Compared with rigid fixation, dynamic fixation showed a significant ROM increase during lateral bending. NZs of fixation segments after dynamic fixation were significantly reduced. There were no significant ROM differences between rigid fixation and dynamic fixation. Conclusions The stability of atlantoaxial joints by dynamic fixation during flexion, extension and rotation was comparable to that by rigid fixation, but weaker during lateral bending. Dynamic screw fixation can maintain the relative stability of atlantoaxial joints.

Establishment of a rabbit model of scoliosis induced by asymmetric load using springs / 南方医科大学学报

<p><b>OBJECTIVE</b>To establish rabbit model of scoliosis induced with stable asymmetric lumbar loads.</p><p><b>METHODS</b>Scoliosis was induced in 10 two-month-old New Zealand rabbits using 316L stainless steel springs placed between the unilateral transverse processes of L2 and L5. Serial radiographs were documented before and at 1, 4, 8, 9 and 12 weeks after the operation. At weeks, the rabbits were randomly divided into SR group (n=5) with the spring removed and SK group (n=5) without spring removal.</p><p><b>RESULTS</b>All the rabbits survived the experiment with Cobb angle all greater than 10 degree at the end of the experiment. Significant changes were found in the Cobb angles and kyphotic angles at 1, 4 and 8 weeks after the operation (P<0.05). At 8 weeks, the Cobb angle, the kyphotic angle and the length of the spring were similar between SR and SK groups (P>0.05), and in the 4 weeks following spring removal in SR group, the Cobb angle and the kyphosis decreased significantly compared with those in SK group (P<0.05). Micro-CT showed that the BV/TV of the concave side was greater than that of the convex side. The length of the spring did not show obvious changes during the experiment (P>0.05).</p><p><b>CONCLUSIONS</b>Asymmetric lumbar loading is a convenient, time-saving, and highly reproducible approach for establishing rabbit models of scoliosis.</p>

Advances in clinical application and biomechanical studies of the posterior dynamic transpedicular screw fixation system / 医用生物力学

It is known that rigid pedicle screw fixation may cause abnormal stress concentration on the posterior part of the spine, which may lead to stress concentration on the fixation device; meanwhile, due to the motion limitation to the fixed segment, the excessive motion at the adjacent segment may further fortify the disc degeneration. To solve these issues, the dynamic fixation is used in clinic, and many studies have investigated the biomechanical mechanism and clinical outcome of the dynamic fixation. The ideal dynamic fixation should meet the following conditions: offering enough stabilization for the fixed segment; reducing the load on the fixation device through enhancing the strain on the anterior vertebral bodies; preventing the degeneration at the adjacent segment; controlling the horizontal shear force at the fixed segment. In this article, the biomechanical properties and clinical application of the posterior dynamic fixation were reviewed and the biomechanical mechanisms of different dynamic fixations were compared.

Balloon inflating and cement filling for treatment of avascular necrosis of the femoral head: a three-dimensional infinite-element study / 南方医科大学学报

<p><b>OBJECTIVE</b>To evaluate the biomechanical changes of balloon inflating and cement filling in avascular necrosis of the femoral head using finite-element analysis.</p><p><b>METHODS</b>The procedure of percutaneous balloon inflating and cement filling was simulated in fresh specimen of human femoral head. CT scan and three-dimensional reconstruction were used to establish the three-dimensional model of the femoral head. The physiological load was analyzed using three-dimensional finite element model to simulate the load and calculate stress on the hip during walking. Finite element analysis was performed on the avascular necrosis model and balloon inflating and bone cement filling model to measure the Von-Mises force at the top, neck and weight-bearing area of the femoral head. Another 8 fresh specimens of femoral head necrosis of human were obtained to stimulate balloon inflating and bone cement filling procedures, and the displacement of the femoral head under different loads was recorded before and after the procedures.</p><p><b>RESULTS</b>After bone cement filling in the necrosis area, the load reduced significantly in the weight-bearing area of the femoral head, and the load distribution became more uniform at the femoral neck and the top of the head. The anti-deformation ability of the necrosis femoral head increased after bone cement filling. The infinite-element analysis and specimen biomedical test showed similar results.</p><p><b>CONCLUSION</b>Percutaneous balloon inflating and bone cement filling in the necrosis area can change the biomechanics mechanism of the femoral head and neck, improve the supporting capacity under load, and prevent the progression of head collapse.</p>

Effects of bioactive modification of poly-D,L-lactide acid scaffolds on the biological behaviors of the seed cells / 南方医科大学学报

<p><b>OBJECTIVE</b>To study the changes in the biological behavior of bone marrow mesenchymal stem cells (BMSCs) transfected with red fluorescent protein by lentivirus (RFP-BMSCs) seeded on in poly-D, L-lactide acid (PDLLA) scaffolds with bioactive modification by ammonia plasma and Gly-Arg-Gly-Asp-Ser (GRGDS) in vitro.</p><p><b>METHODS</b>Circular sheets of PDLLA scaffolds (8 mm in diameter and 1 mm in thickness) were prepared and aminated with PDLLA (group A) or modified with the peptide conjugate A/PDLLA (group PA), with untreated PDLLA as the control (group P). The RFP-BMSCs were seeded on the scaffold materials and their proliferation and metabolic activity were detected using CyQuant NF and Alamar blue staining. The mineralization on the scaffolds was observed using calcein fluorescent dye under a fluorescent microscope. The adhesion and proliferation of RFP-BMSCs were observed by fluorescent microscope, and scanning electron microscope (SEM) was used to confirm the observed adhesion of the seed cells.</p><p><b>RESULTS</b>The RFP-BMSCs seeded on the 3 scaffolds all showed proliferative activity at different time points after cell seeding, and the cell numbers decreased significantly in the order of PA>A>P (P<0.001). The cell number was significantly greater in group PA than in group A at all the time points except for days 10 (P=0.077) and 12 (P=0.491), and gradually became similar with the passage of time. The metabolic changes of the cells follow a similar pattern of cell proliferation. RFP-BMSCs showed more active proliferation in group A and group PA than in group P. On days 14 and 21, the intensity of green fluorescence decreased in the order of group PA, A and P. The RFP-BMSCs showed better adhesion in group PA than in group A, and the cells in group P appeared more scattered under scanning electron microscope.</p><p><b>CONCLUSION</b>Bioactive modification of PDLLA by ammonia treatment and conjugation with GRGDS peptides may promotes the adhesion, proliferation, metabolism and mineralization of RFP-BMSCs seeded on PDLLA scaffolds.</p>

Histology and proliferative capability of thoracic vertebral body growth plates of rats at different ages / 南方医科大学学报

<p><b>OBJECTIVE</b>To compare the histological features of the thoracic vertebral body growth plates (VBGPs) of rats at different ages and assess their proliferative capability.</p><p><b>METHODS</b>The thoracic VBGPs obtained from rats aged 1 day and 1, 4, 8, 16 and 28 weeks were identified using safranin O-fast green staining, and the height of the hypertrophic zone, proliferative zone, and resting zone were measured. The chondrocytes were isolated from these VBGPs with a modified trypsin-collagenase type II digestion method for primary culture in vitro. The expressions of proliferating cell nuclear antigen (PCNA) mRNA and protein was detected by real time-PCR and Western blotting, respectively.</p><p><b>RESULTS</b>The 1-day- and 1-week-old rats showed significantly greater hypertrophic zone and proliferative zone in the VBGPs than older rats (P<0.01); the proliferative zone was significantly greater in rats aged 4 weeks than in those aged 28 weeks (P<0.05). The resting zone was obviously greater in rats aged 1 day and 1 week than in older rats (P<0.05), and also greater in rats aged 4 weeks than in those aged 16 and 28 weeks (P<0.05). Obvious ossification in the resting zone occurred at 16 weeks, and most of the resting zone became ossified at 28 weeks. The expression of PCNA decreased at both the mRNA and protein levels as the rats grew.</p><p><b>CONCLUSION</b>The 3 zones of VBGPs are greater in rats aged 1 day and 1 week than in older ones. Ossification in the resting zone begins at 16 weeks, and till 28 weeks, most of the resting zone is ossified. The proliferation ability of VBGP chondrocytes decreases with the increase of age of the rats.</p>

The effect of disc degeneration on the structural property distributions in the cervical vertebral endplates / 中华外科杂志

<p><b>OBJECTIVE</b>To study the effect of disc degeneration on the structural property distributions in the cervical vertebral endplates.</p><p><b>METHODS</b>A 2 mm-diameter hemispherical indenter was used to perform indentation tests at 0.03 mm/s to the depth of 2 mm at 20 normalized locations in 50 bony endplates of intact human cervical vertebrae (C2 approximately C7). The resulting load-displacement curves were used to extract the failure load and stiffness of each test site. Grade of disc degeneration was determined using Nachemson's grading scale. One-way ANOVA, factorial analyses, SNK tests and correlate analyses were used to analyze the result data.</p><p><b>RESULTS</b>Both the failure load and stiffness decreased with disc degeneration in the cervical endplates (P <0.001, both), and correlated significantly with the disc degeneration (rs=-0.429 and rs=-0.244, respectively). Only the distribution of superior cervical endplate changed with disc degeneration, but that of inferior cervical endplate changed little.</p><p><b>CONCLUSIONS</b>The structural property distributions in the cervical vertebral endplates change significantly in the degenerated discs. It suggests that disc degeneration is an important factor to evaluate the intervertebral implant subsidence in anterior cervical fusion.</p>

Stability analysis of an enhanced load sharing dynamic pedicle screw fixation device and its equivalent rigid device / 中华外科杂志

<p><b>OBJECTIVES</b>To compare the stability of an enhanced load sharing dynamic pedicle screw fixation device with its equivalent rigid device and to evaluate biomechanical roles of the dynamic fixation.</p><p><b>METHODS</b>A model of L(1) body fracture was produced on seven specimens of fresh adult cadaver spine from T(10) to L(4). Both dynamic and rigid devices were applied in the specimens to strength the injured level. Ranges of three dimensional movements and stiffness under flexion-compression were measured in intact, injured and stabilized specimens.</p><p><b>RESULTS</b>Both dynamic and rigid devices were found to provide significant stability for injured segment in flexion-extension and lateral bending. In axial rotation, the devices could restore the stability to levels similar to those in an intact spine. Results indicated 40% increase in range of motion in flexion-extension and 24.1 Nmm reduction in stiffness of flexion-compression for dynamic device, compared with the rigid device.</p><p><b>CONCLUSION</b>The dynamic device offers a design that may enhance load sharing without sacrificing the stability and will decrease stress-shielding and stress concentration.</p>

Biomechanical Evaluation on Cervical spine stabilizing Effects of Cervical Interbody Spinal Fusion Using Allograft Fusion Cage / 中华骨科杂志

Objective\ To evaluate the immediate effects and strength of allograft fusion cage(AFC) used for reconstructing stability of cervical spine. Methods\ Discs of C 5 and C 6 were resected on 8 fresh human cervical spine specimens, and autogenous iliac bone grafts(AIBG), and AFCs were implanted into the intervertebral spaces respectively. Compression test, pull out test and segmental motion measurement were studied.Results\ Comparing with intact and AIBG groups, the range of motions of C5-6 in AFC group were decreased in all directions except for extension; with (502?114) N compressive load,the vertebrae in AFC group were broken while the AFC were intact, but the AIBG were broken at (135?42) N load; with 300 N drawing load,no loosening was found between AFCs and vertebra, but it was found between AIBG and vertebra at 60 N load. Conclusion\ AFC could provide enough support,anti slide ability and could remain or increase the height of intervertebral spaces. It completely meets clinical and biomechanical requirements.