Histopathological Changes Of Acute Tibial Osteomyelitis In Rabbits

【Background】Osteomyelitis is an infectious disease that affects bone and bone marrow,causing great loss of human life and property.Staphylococcus aureus has the highest probability of infection.The treatment of Staphylococcus aureus osteomyelitis is still a huge challenge,so rapid and accurate diagnosis is particularly important.As one of the gold standard histologicaldiagnosis is still mainly using neutrophils as the diagnostic criteria.However,to propose a new histopathological diagnostic criteria,it is necessary to have a sufficient understanding of the histopathological manifestations and the process of changes of osteomyelitis.At the same time,there is still no unified clinical standard for the resection range of bone infection in acute osteomyelitis,and the histomathological changes of bone cortex have importantguiding significance for the surgical clearance of the range of bone infection.At present,the histological description of osteomyelitis is mostly observed through clinical cases,and there is a lack of pathological changes with a clear time of infection,especially the tibial cortical histological changes in acute osteomyelitis,which has not been described yet.Therefore,in this study,a rabbit model of acute osteomyelitis of the tibia was constructed to observe the histopathological changes of the tibia at different times of acute osteomyelitis caused by S.aureus,so as to provide a basis for the study of acute osteomyelitis.【Methods】Thirty-six healthy adult New Zealand rabbits were selected and randomly divided into 3,7and 14 day control groups with 6 rabbits in each group,and 3,7 and 14 day experimental groups with 6 rabbits in each group.The bone window was made in the middle segment of the tibia of the left posterior limb of New Zealand rabbits by orthopedic electrosurgery.The experimental group was injected with 20ul of Staphylococcus aureus with a concentration of1*10~7CFU into the medullary cavity,and the control group was injected with 20ul ofnormal saline.The rats were fed for 3 days,7 days and 14 days after surgery,respectively.The evaluation and analysis were performed by general conditions,microbiology,transmission electron microscopy,and histopathology.【Results】Staphylococcus aureus of 2*10~5CFU was infiltrated into the middle segment of the tibia of rabbits,and the infection symptoms of different degrees appeared in the experimental group on 3,7 and 14 days after operation.The infection rate of the experimental group was 100%by microbial culture.The presence of S.aureus in cortical bone was not observed bytransmission electron microscopy at 7 days,but scattered S.aureus was observed in lacunae at 14 days.Histopathological observation showed that periosteal reaction and fibroplasiaappeared within 3 days of S.aureus acute tibial osteomyelitis,and were observed in thefollowing 7 and 14 days.At this time,granulation tissue and scattered neutrophils appeared in some specimens.On the 7th day,the thickness of periosteal reaction on the soft tissue side of cortical bone increased,and the other structures did not change significantly.Bonenecrosis and bone erosion in the medullary cavity side also began to appear at this time,but no obvious bone damage and haversian canal expansion were found in the cortex bone.Most of the specimens in the medullary cavity had neutrophil aggregation,and the necrotic cells and other inflammatory cells formed micro abscess.On the 14th day,the soft tissue side of cortical bone had no obvious change compared with that of the 7th day group.Bonedestruction and the enlargement of Haversian canal appeared on the side of cortical bone marrow cavity.Dead bone slices,micro abscesses and cellulose necrosis could be seen in the medullary cavity.Scattered plasma cells and neutropenia could be seen in somespecimens.【Conclusion】1.A rabbit model of acute osteomyelitis in the tibia could be continuously induced by injecting 2*10~5c FU Staphylococcus aureus to the middle segment of the tibia window.2.From 7 to 14 days after infection,the invasion of Staphylococcus aureus into the bone lacunae in the bone cortex can be observed by transmission electronmicroscope.3.Histopathological observation showed that periosteum reaction and fibroustissue hyperplasia were observed within 3 days after acute tibial osteomyelitis modeling and were observed in both the 7 and 14 day groups.Neutrophils and granulation tissues appeared in some specimens,but no significant changes were observed in the bone cortex of thelateral medullary cavity.By 7 days,neutrophils had accumulated in the medullary cavity in most of the specimens,and small microabscesses were formed along with necrotic cells and other inflammatory cells.Osteonecrosis and bone erosion in the lateral bone cortex of the medullary cavity also began to appear at this time.On the 14th day,dead bone slicesappeared,microabscesses became more severe,and cellulose necrosis could be seen.Bone destruction and Harvard tube enlargement appeared in some specimens,and plasma cells began to appear and gradually replaced neutrophils.Within 7 days of exposure to S.aureus in acute osteomyelitis of rabbit tibia,the changes of bone cortex were not obvious,and no S.aureus was found in the lacunae,so the intraoperative debridement did not require extensive cortical excision.By 7 to 14 days,the infected bone tissue on the side of the medullary cavity should be removed appropriately according to the intraoperative situation.In our study,we described the histopathological changes during the acute period of osteomyelitis based on the specific time of infection,which is helpful to understand the pathogenesis ofosteomyelitis,and also provides a basis for the diagnosis and treatment of acute osteomyelitis with S.aureus in clinical practice.