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The Experimental Study of Biodegradable Cage Made by Pure Magnesium and the Imageological Measurement of Sternoclavicular Joint and Its Clinical Application

Author: LiMing
Tutor: ZhangYingZe; PanJinShe
School: Hebei Medical University
Course: Surgery
Keywords: magnesium interbody fusion posterior decompression pedicle screw internal fixation biomechanics absorbable material calciumphosphate sternoclavicular joint imageological measurement dislocation
CLC: R687.3
Type: PhD thesis
Year: 2012
Downloads: 73
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Abstract


With the accelerated aging of the society, lumbar degenerative disease is becoming an important factor which interferes with people’s health and quality of daily life. Lumbar degenerative disease is a natural process, and also a kind of self-protection mechanisms. Diagnosis and treatment of lumbar degenerative disease remains a great challenge for orthopedic surgeons and a research focus in the orthopedic field.Degeneration of the nucleus is considered to be the start-up point of the lumbar degenerative disease. Water content and elasticity of the nucleus decreased with aging, which leads to re-distribution of the spinal load, followed the spine structure degenerating gradually. Meanwhile, nucleus degeneration also results in narrowing of the intervertebral disc space. Furthermore, the nucleus was protruded to the compress nerve root. All these factors contributed to the pain of the affected lumbar and leg. At the beginning of spinal degeneration, many supernumerary structures, such as hyperplasia formation of osteophytes, ligamentum flavum hypertrophy and hyperplasia of the articular process can response to this change as the body’s own regulation. The above mentioned structures could be regarded as primary body structure to increase the stability of the spine. However, one coin has two sides:these degenerative protection structures compress the nerve root or spinal cord, leading to clinical symptoms, disturbing the daily life. So the surgical treatment of lumbar degenerative disease gains its popularity by removing the hyperplasia structure, restoring the normal alignment of the spine, or reconstructing spinal stability.Posterior lumbar interbody fusion with the aim to release compression of the nerve root by removal of proliferation structure has been the standard surgical interbody fusion since it was introduced by Cloward in the1950s. The technique can remove the proliferation of various structures, complete the internal fixation and insert the cage to the position adjoining the mechanical center maximatily. After removing the proliferation structure, restoration of the spine normal sequence and the reconstruction of spinal stability have become the focus of the subsequent research. The treatment of intervertebral space is a key point.Interbody fusion technology can provide a stable and fast convergence after decompression. Autologous bone transplantation in the intervertebral space can promote the fusion of the spine to ensure stability. But it is found in clinical practice that the bone graft used in fusion interbody does not have adequate intensity for the early load-bearing. The bone graft may collapse or be absorbed during remodeling and integration of the bone. Complication in bone donor site has also been reported. The metal cage can effectively restore the height of the intervertebral space, and avoid complications of bone donor site at the same time. However, there are some disadvantages about metal cage because of the high modulus of elasticity such as stress shielding, sink, shift, and interfereing with radiological observation. Therefore, material with the elastic modulus similar to vertebral bone such as carbon fiber and PEEK is the optimal selection for cage implamtation. These materials have good radiolucent features, and approximate shape similar to endplate. But it’s also reported that inflammatory cells appear around the transplanted material. With the technology and multidisciplinary development, absorbable materials such as polylactic acid have been brought into clinical application. It has been found that the absorbable material can provide immediate stability and will be gradually absorbed during the interbody fusion process to improve the intervertebral fusion rate with fewer complications. Whereas, the acidic metabolites from the absorbable fusion devices can lead to osteolysis. The time to absorbe the degradation fusion material is varied among different reports. It is vital to resolve the above mentioned problems by identifying the new material not only with elasticity similar to bone but also with ability of gradual degradation.The history of magnesium application in the orthopedics can be traced back to1878. Pure magnesium has many characteristics, including1, elasticity modulus similar to bone, avoiding excessive cutting the end plate;2, bone inducibility and biodegradation which can promote interbody fusion process;3, its metabolites harmless to humans.4, Promoting the healing of fracture. In addition, it has been also reported magnesium can promote bone growth and recovery of nerve function. However, the application of magnesium is limited as a kind of orthopedic fixation materials for its excessive degradation speed in human body.Considering the demands of interbody fusion and the characteristics of magnesium, we cooperate with The Metal Institute of Chinese Academy of Sciences and The Nathon Medical Group in Beijing to conduct two studies:1, coating magnesium with Ca/P as an interbody fusion and exploring its degradation characteristic in interbody fusion;2, investigating the healing time of the dislocation of amphiarhtrosis for the application of magnesium as a kind internal fixation. In the current study, we design magnesium cage according to the animals through experimental animals’spine imaging measurement and coat the magnesium cage with Ca/P. Then we implanted the magnesium cage to the intervertebral space by the posterior interbody fusion. Finally, we study the degradation characteristics of the magnesium in vitro and in vivo.Part1The design and manufacture of pure magnesium cage according to the imaging measurement of goat lumbar imaging dataObjective:To measure the anatomical parameters of the goat’s lumbar spine for the design and manufacture of pure magnesium cage.Methods:Methods:Using the Siemens64-slice spiral CT scan to scan lumbar spines of12goats. These images were reconstructed. The measurement software accompanied with CT workstation was used to measure the vertebral body height, disc space height, the height and width of the pedicle and the endplate area, etc. Based on these measured data, the pure magnesium cage was designed by CAD software. Results:Posterior vertebral body height (VBHp) increases gradually to3.32±0.14cm in L6, and narrowes to0.57cm in L7. The anterior vertebral body height (VBHa) has the same tendency with VBHp, and maximizes to2.78±0.01cm in L6. Posterior border is higher than anterior border in the lumbar vertebral body.The endplate width gradually increases to1.92±0.03cm from L1to L3, decreases to0.99±0.02cm sharply in L4, and increases gradually to2.53±0.02cm in L7. The value of EPAu is407.63±2.52mm2, becomes smaller (about364.24±2.64mm2) in L2.The value of EPAu is393.65±2.52mm2in L3, and decreaed gradually to L6, then increased sudduenly to464.00±3.59mm2in L7.The value of EPAl shows similar trend to EPAu.The SCW gradually widened to2.61±0.19cm in L7. The SCD increased gradually tol.15±0.01cm in L7.The value of PDWL is largest in Ll (0.70±0.03cm) and decreases to0.45±0.02cm in L4, then increases to0.62±0.02cm in L6, decreases to0.53±0.02cm in L7. PDWR is similar to PDWL, and no statistical difference between these two groups. The average value of PCA is42.00±, and increases to57。in L7. There is no statistical difference between both sides.The height of the front intervertebral disc increases gradually to1.37±0.03cm in L6-7, and decreases to1.27±0.04cm. The height of the post intervertebral disc is similar to this trend, but smaller than the front value.Conclusion:The anatomical parameters of goat lumbar spine has been measured, and based on these parameters, pure magnesium cage has been successfully designed and manufactured. These data are helpful to handle surgery and choose internal fixation.Part2The vitro degradation characteristics of pure magnesium cage coated with calcium phosphateObjective To test degradation characteristics of pure magnesium cage coated with calcium phosphate in the simulated body fluid.Methods Pure magnesium cages were placed in calcium nituate tetrahydrate phosphate and sodium dihydrogen calcium phosphate deposition solution at70℃for12h. The characterization of the morphology and composition of the coating layer were determined by electron microscopy. The degradation and surface activity of magnesium coated with calcium phosphate were studied in Hank’s simulated body fluid.Results:Electron microscope image scanning showed that the magnesium matrix was coated compactly with a layer of polygonal granular calcium phosphate crystals. The coating layer was smooth and regular, and integrated closely with magnesium matrix. The thickness of layer is about23μm. The results show that the coating layer was mainly composed of Ca, P and O elements by EDS. There is no Mg peak in the spectrum. It was confirmed that the magnesium matrix was covered with the layer composed of c calcium phosphate. The pH value of leaching solution which contained uncoated magnesium cage without the treatment of calcium and phosphorus soon reached to11.3on the first day. This phenomenon indicated that the magnesium matrix was corroded severely. Then, the pH value began to show a slow descent. On the comparison, the leaching solution’s pH value of magnesium that coated by calcium and phosphorus only rose to7.8on the first day, and then the pH value rose slowly until the10th day when the pH value began to show a slow descent. The pH value to leach solution containing coated magnesium was still lower than9until the20th day, compared with the pH value of the above solution equal to10.18on the same point. The phosphorus was showed below in the Hank’s solution for110days. As shown, the surface of coated magnesium surface was still compactly covered with calcium phosphate crystals in Hank’s solution, indicating that the coating layer was not completely degraded at110days, and still protected magnesium matrix. EDS analysis of the coating layer after the coated magnesium immersed in SBF for110days showed that the main elements of the coating layer was still the O, Ca and P. Ca/P atomic ratio increased from1:1to1.7after immersion. The ratio was close to hydroxyapatite (1:5), indicating that the hydroxyapatite HA was generated on the surface of magnesium cage coated with Ca/P in Hank’s solution. Conclusion:The magnesium can be coated successfully with calcium phosphate through the chemical deposition method. Magnesium coated by calcium and phosphorus owned good resistance to corrosion. The coating layer has not been completely degraded and still protected magnesium matrix in SBF for110days. HA might be generated on the surface, which has biological activity.Part3The biomechanical study of pure magnesium cage in vitroObjective:To evaluate the effect on lumbar movement segment fixed with pure magnesium cage combined with pedicle screw fixation.Methods:Twelve goats’L4-L5motion segments were randomly averaged into3groups. The first group is the normal specimens as the control group. The second group was the cage group, in which the specimens were operated using the standard PLIF, and the pure magnesium cage was implanted in the intervertebral space. The third group was interbody autologous ilium group, treated same to the second group, but autologous ilium was inserted into the interbody. Specimen was fixed on the CSS-440020biomechanical testing machine, and the strain gauges were pasted on the16selected sites distributed uniformly on the upper and lower vertebral body. The strain value was measured by WS3811digital strain gauge when the loads increased to500N gradually.Results:Normal group:stress concentrated on the front part of the vertebral body, and the displacement of the anterior sites increased significantly. The displacement of normal groups was largest among three groups.Cage group:Axial displacement of various sites increased uniformly, and the displacement in Cage group was the smallest among three groups.Autologous ilium Group:The displacements of all sites increased uniformly, and the displacement in autologous ilium Group was greater than that in Cage group.In the flexor test:the displacement was largest in the normal group while smallest in the cage group. In the test of flexion and extension, the displacement in cage group is smaller than that in autologous ilium group. But there was no statistical significance between both groups. The displacements in these two groups were significantly smaller than in normal vertebral group.Conclusion:The vertebral motion segment fixed with the pure magnesium cage combined with pedicle screw can provide a good mechanical stability for interbody fusion. Part4:The study of the interbody fusion and degradation of pure magnesium cage in goatObjective:To observe the bone formation and the degradation of pure magnesium in the goat intervertebral space.Methods:Twelve1-year-old male goats, with as average weight of52kg, were randomly divided into2groups (n=6). The first group is pure magnesium cage group. The goat in this group was conducted with posterior lumbar interbody fusion (PLIF) in the L4-L5segment after anesthesia. Interbody fusion material was pure magnesium cage. The second group was autologous ilium group treated through the surgical approach same to the first group, but autologous ilium was acted as interbody fusion material. CT scanning was carried on the1st week, the2nd weeks, the4th weeks, the8th weeks, and the12th weeks after the surgery, respectively. The degradation and bone formation of two kinds of materials were observed. The blood samples of goats were collected to monitor blood magnesium. The animals were executed at3months later after the surgery, and the L4-L5segment of these animals were removed and examined by micro-CT scanning to investigate the degradation and fusion of the implant, compared with six normal vertebral as control. Heart, liver, kidney of the goats were sliced and examined under light microscopy to investigate the changes in these organs.Results:There was no significant difference in different phase between two groups. CT imaging showed that there were no loosening and displacement of the internal fixation. There was no apparent gas appearance adjacent to the pure magnesium cage. With time passed by, the density of pure magnesium cage absorbed?? grandualy, indicating that the coating layer was gradual degraded. At four weeks after the surgery, newborn bone appeared around the intervertebral plant material. Micro-CT showed that osteoporosis was observed in all fixed vertebral segments. Intervertebral bone trabecular appeared in both groups. There was less number of newborn trabecular in pure magnesium cage group, while more mature bone trabeculars were found which was relatively strong. At three months after the surgery, the coating layer began to degrade. The pathological sections of heart, liver, and kindey slices in both groups showed no significant pathological changes.Conclusion:Pure magnesium cage coated with the calcium phosphate degrades slowly in vivo and has good biocompatibility. Moreover, the new-style cage can induce osteogenesis and provide effective intervertebral support.Part5The imageological measurement of sternoclavicular joint and its clinical applicationObjective:To investigate its imageological anatomical features, and facilitate therapy of SCJ dislocation.Methods:Fifty healthy Chinese volunteers examined with chest computed tomography (CT) in our hospital were included into the study. Volunteers with SCJ deformity or injury were excluded from the study. The coronal, sagittal and axial images of the sternoclavicular region from the superior border of the clavicle to sternal angle were reconstructed. The diameter of the sternal head in inferolateral to superomedial direction(DOSH), the length of clavicular notch and the angle between clavicular notch and sternum were measured on the coronal images. The angle between presternum and trunk were measured on the sagittal images. The following issues were measured in the axial images, including (1) the anteroposterior dimensions of sternal head, clavicular notch and presternum;(2) the SCJ wide;(3) the distance between bilateral clavicles; and (4) the minimal distance from presternum to the underlying structures in the thoracic cavity. New plate was designed according to the data measured in the study to treat SCJ dislocation or subluxation. Results:The proximal clavicle is higher than the prestenum in a horizontal position. On the axial images, the anteroposterior dimension of the sternal head was longer than the presternum, and the center region of the presternum was thinner than the edges. The left SCJ space was0.84±0.24cm, and the right was0.88±0.23cm. Among the structures going behind the sternum in the thoracic cavity, the left bilateral innominate vein ran nearest to the presternum. The distance from the anterior cortex of sterna to left bilateral innominate vein was2.38±0.61cm. A new-style plate was designed according to our measurement. Anatomical reduction of the dislocated joint and safe insertion of screws into the presternum was achieved in the management of SCJ dislocation with the use of the new plate.Conclusion:Normal parameters of the SCJ were measured on the CT images. The measurement can facilitate the treatment of SCJ dislocation or subluxation. The new designed plate can be used to treat SCJ dislocation effectively and safely.

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CLC: > Medicine, health > Surgery > Orthopaedic Surgery ( movement system diseases,orthopedic surgery ) > Orthopedic surgery and surgery > Bone surgery
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