| OBJECTIVE: To measure the regional characteristics of the microstructure of patella and patellar enthesis,and the effect of different interventions on regional characteristics by Micro-CT.To explore the relationship between the microstructure damage of enthesis and related regional characteristics,and try Establish a feasible method to reflect the pathological regularity of microstructural damage of enthesis by using Micro-CT.Methods: 42 New Zealand white rabbits were randomly divided into 7 groups: blank control group(CON),acute injury control group(Accon),acute postinjury rest group(AcR),acute postinjury low intensity exercise group(AcL),chronic injury control group(Chcon),chronic postinjury rest group(ChR),and chronic postinjury low intensity exercise group(ChL).In the experimental group,acute or chronic injury models were made according to the methods previously established in our laboratory,and different recovery methods were intervened after modeling.After the intervention,The samples were scanned by micro-CT after each group was taken,and then through image reconstruction,different gray value range and regions of interest were selected.Finally,bone volume fraction BV/TV,bone trabecula number Tb.N,bone trabecula separation Tb.SP,porosity Po(tot),bone trabecula connection density Conn.D,average bone cross-sectional area B.Ar and average cross-sectional thickness Cs.Th,fractal dimension FD and other related microstructure indexes were measured.Fifteen division method was used for the whole patella to measure the regional characteristics of normal patella microstructure and the influence of different intervention methods on it;three division method was used for the enthesis to measure the regional characteristics of cartilage microstructure and the influence of different intervention methods on it;finally,one patella in the blank control group was selected for three-dimensional reconstruction,and then the finite element simulation analysis of the stress on patella patellar tendon is carried out.Results:(1)In the nine parts of normal patella PC1-PC3,PL1-PL3,PM2 and PM3,the indexes of bone microstructure were more intensive;As far as the whole patella is concerned,before and after modeling,the bone microstructure in most parts of patella did not change significantly.Before and after intervention,the indexes of bone mass in AcR group decreased significantly,and those in AcL group were significantly higher than those in Ac R group;The parts involved were mainly mainly the center and lateral high stress areas;(2)The cartilage-related microstructural indicators of the Chcon group,ChL group and ChR group were significantly higher on the lateral side than on the medial side;Compared with the model before and after modeling,except for the index FD on the medial and middle parts of the acute group,the Accon group was significantly higher than the CON group.No significant difference was seen.and the index of cartilage microstructure in the lateral part of Chcon group was significantly higher than that in CON group.the indexes of FD and B.Ar in ACL group were significantly lower than those in Accon group,and the indexes of cartilage related microstructure in ChL group were significantly lower than those in ChR group.(3)Finite element simulation shows that,except the high stress area at the two enthesis,the overall patellar stress gradually decreases from lateral,top to medial,bottom,and the stress distribution at the enthesis is the highest on the lateral.These results are consistent with the the regularity of the site of injury in the previous two studies.Conclusion:(1)The stress on the lateral side of the patellar enthesis of the rabbit was the largest,and the method of chronic injury modeling with 30% maximum knee extension force for 4 weeks has increased the difference between the medial and lateral sides.(2)No matter acute or chronic injury model,the changes of the microstructure of patella in rabbits are only limited to the cartilage layer of enthesis.The recovery way of rest for 4 weeks after injury is not conducive to the recovery of patella microstructure in rabbits.Compared with low-intensity recovery exercise,it is better to promote the microstructure of the whole patella or the cartilage microstructure at enthesis Into the recovery.(3)Micro CT technology with gray value range of 45-75 is used to reconstruct cartilage area,which has the characteristics of noninvasive and intuitive reflection of morphological changes,and is of practical significance for its structural research.The fractal dimension FD is a sensitive technical index for the evaluation of cartilage surface roughness.The finite element simulation shows that the stress of the patella and the enthesis of the patella is basically in accordance with the law of the injury site in the first two parts of the study,which is verified by each other,and establishes a reasonable and effective finite element method for the future related research. |
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