| Iliac autografts has been the golden standard of bone grafting in anterior cervical fusion since Smith and Robinson first performed anterior cervical discectomy and fusion in 1958. However, harvesting autografts has some disadvantage such as pain and infection of harvested sites, tear fractures, nerve injuries, limited supply, increased surgical time, and so on. Because of above mentioned disadvantage many scholars have always strived to seek ideal bone substitutes.Allograft or xenograft bone has been successfully applied in experimental studies and clinical trials because of its osteoconductivity and relative widely resources. But it is still a main concern that the risk of immunological rejection and potential transmitted virus such as type B or C hepatitis virus, human immunodeficiency virus.Although it can avoid harvesting iliac bone grafts by the means of using the local bone obtained from decompression combined with the titanium mesh or cage, sometimes there is less local bone available for use. There are some studies reported that the dislocation rate of titanium mesh or cage was about 17 percents and the subsidence rate in upper and caudal vertebrae were 42 percents and 50 percents respectively. So this method has limited use.With the development of materials technology and biomechanics, the research related to synthetic bone substitutes has been more extensive. Now the most used bone substitutes are calcium sulphate (CS) and calcium phosphate. The latter is mainly composed of hydroxyapatite (HA) andβ-tricalcium phosphate (β-TCP). All These synthetic materials enjoy several advantages over other bone graft materials in that they are osteoconductive, nontoxic, biocompatible, easy to sterilize and available in a virtually unlimited supply. However, they have some disadvantages. Firstly, they are not osteoinductive and osteogenic. Secondly, they have different duration of degradation. The resorption of some materials are rapid, such as calcium sulphate which was absorbed four to six weeks after implantation. At that time the new bone formation is incomplete and the fusion mass is weak, this may lead to breakage of plate system. HA is a relatively inert substance that is retained in vivo for prolonged periods of time, and it can provide structural stability.β-TCP typically undergoes biodegradation within 8-12 weeks of its introduction into the area of bone formation.There are many reports about CS andβ-TCP as bone expander for repairing non weight-bearing bone defects, whereas rare are applied in anterior cervical fusion. In order to obtain ideal substitutes for anterior cervical fusion, we planed to investigate the effect of CS andβ-TCP applied in anterior cervical fusion.To mimic human cervical spine surgery more accurately, it has best to use non human primate as models. However these animals are expensive, limited supplying and difficult to handle, many scholars most use goat, sheep and swine as animal models. By far, the comparison of three-dimensional biomechanics between goat and human are rare reported. It still remains concern about whether goat is a optimal model for anterior cervical spine surgery. To solve this problem, it needs to compare the three-dimensional biomechanics of goat and human.In addition, the bone grafts used in anterior cervical interbody fusion require supporting gravity of head, so it should be to investigate biomechanical stability of CS andβ-TCP in vitro. And rare reports have addressed this issue up to now.In general, we planed to investigate biomechanical stability of CS andβ-TCP, compare the three-dimensional biomechanics between goat and human cervical spine, establish optimal model for anterior cervical fusion and observe the fusion effects of CS andβ-TCP as bone substitutes. Our study made up of three parts as follow.Part one: Comparison of Three-dimensional Biomechanical Characteristics Between Goat and Human Cervical SpineObjective. To compare three-dimensional biomechanical characteristics between goat and human cervical spine.Methods. Eight fresh cervical spines were harvested respectively from adult human cadaver and pure breed ChongMing white goat. And the range of motions(ROM) and neutral zone(NZ) of the specimens were tested respectively in three-dimentional testing apparatus under flexion, extension, right or left bending and axial rotational loads.Results. Under flexion loads, ROM of C1-2 of goat and human are 16.9±5.1 and 14.3±3.2 degrees respectively, lager than other levels. But the ROM and NZ of each level of cervical spine of goat has no statistical significance respectively when comparing with human (P>0.05). Under extension loads, ROM of C1-2 of goat and human are 20.6±4.8 and 18.7±3.7 degrees respectively, and ROM of C0-1 of goat and human are 19.3±4.7 and 18.4±4.3 degrees respectively, more superior than other levels. But the ROM and NZ of each level of cervical spine of goat has no statistical significance respectively when comparing with human (P>0.05). Under axial torques, ROM of C1-2 of human is 56.3±8.9 degrees, made up of 70 percents of ROM of the whole cervical spine. And ROM of C1-2 of goat is 56.3±8.9 degrees, made up of 68 percents of ROM of the whole cervical spine. NZ of C1-2 of goat and human are 25.9±7.1 and 29.6±6.5 degrees respectively, made up of most of whole cervical spine. However, the ROM and NZ of each level of cervical spine of goat has no statistical significance respectively when comparing with human (P>0.05). Under right or left bending loads, the ROM of each level of cervical spine of goat has no statistical significance respectively when comparing with human (P>0.05). Except C6-7 level, the NZ of other levels of cervical spine of goat have no statistical significance when comparing with human (P>0.05).Conclusions. Pure breed ChongMing white goat had similar biomechanical characteristics with human under flexion, extension, right or left bending and axial rotational loads. It served as an optimal model for anterior cervical fusion and biomechanical research.Part two: Biomechanics of CS andβ-TCP in Vitro Compare with Human Freeze-drying Iliac AllograftsObjective. To investigate the axial compression strength and elastic modulus of CS,β-TCP and human freeze-drying iliac allografts.Methods. Respective eight pieces of CS,β-TCP and human freeze-drying iliac allografts in same size (3cm×1.5cm×1.0cm) were obtained for mechanical testing. Each specimen was mounted in testing apparatus, loaded axial compression with a velocity of 1mm per second and the load–displacement curves were plotted. Thus the axial compression strength and elastic modulus were calculated.Results. The axial compression strength of CS,β-TCP and human freeze-drying iliac allografts were 3.26±0.86Mpa, 3.16±0.75 Mpa, 2.97±0.81 Mpa respectively, and elastic modulus were 82.35±10.54 Mpa, 76.98±11.78 Mpa, 35.35±6.98 Mpa. The axial compression strength of CS andβ-TCP have no statistical significance when compared with human freeze-drying iliac allografts. However, the elastic modulus of both were lager than human freeze-drying iliac allografts (p<0.05).Conclusions. CS andβ-TCP had optimal structural supporting stability. Part three: Evaluation of Efficacy ofβ-TCP and CS as Bone Substitutes for Goat Anterior Cervical Fusion.Objective. To evaluate efficacy ofβ-TCP and CS as bone substitutes for goat anterior cervical fusion.Methods. twenty four pure breed adult ChongMing white goats were divided into three groups(group CS, groupβ-TCP and group auto) equally and randomly. And the animals were performed with anterior C3-4 discectomy and fusion with different grafts according to preoperative plan. all animals were tested by means of X-ray in 1th, 6th , 12th and 24th week after operation. And the three-dimensinal CT reconstruction were performed in 12th and 24th week. After all animal were euthanized in 24th week, Cervical plate systems were removed and biomechanical testing was performed in non destructively. And then histomorphological and histomorphometrical analysis of decalcified and non decalcified slices were carried out.Results. Radiograph of six weeks postoperative revealed CS began to absorbed. Radiograph and CT reconstruction in 12th week postoperative suggested that there was only one animal obtaining complete fusion in group CS whereas 4 and 5 respective in groupβ-TCP and Auto. In 24th week the number of complete fusion still remained one in group CS, but 5 and 6 respective in groupβ-TCP and Auto. The biomechanical testing revealed that ROM of C3-4 of groupβ-TCP and Auto decreased compared with group CS. It was observed in HE stained slices that less new bone formation, Cartilaginous tissue and massive fibrous tissue in group CS while massive mature trabecular bone and mallow in groupβ-TCP and Auto. There was a small quantity of ceramic Remnants in groupβ-TCP. The new bone formation rate was 25.8±5.1%, 45.5±6.7%, 49.2±5.8% respectively in group CS,β-TCP and Auto. There was no statistical significance between groupβ-TCP and Auto (P>0.05), while statistical significance was seen in group CS when comparing with groupβ-TCP or Auto (P<0.05).Conclusions.β-TCP had similar efficacy with autografts in anterior cervical fusion and was superior to CS.β-TCP is an optimal substitute for iliac autografts.
|
PDF Full Text Request