| Anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) are the important structures of the knee joint because of their contribution on joint stabilization and restriction of tibia and femur.With the increasing incidence of traffic accidents and sport-related injuries, the incidence of PCL ruptures goes up as well. More and more attentions are paid to this pathological event. However, there are still some controversies on the treatment of the PCL rupture. Some clinicians hold the view that simple PCL rupture should be cured using non-opertive therapy, but some doctors reported the results of long term follow-up on non-operative therapy were not as good as expected.The effect of PCL rupture on ACL is not clear from literature. This project was aimed to investigate the biomechanical and histological alterations of ACL in the PCL-ruptured knee. At first, We measured the strain of ACL anteromedial bundle (ACL-AMB) and ACL posterolateral bundle (ACL-PLB) under the conditions of PCL intact, PCL anterolateral bundle (ALB) dissected, PCL posteromedial bundle (PMB) dissected and PCL complete dissected in order to clarify the exact biomechanical change of ACL stress in PCL-ruptured knee. Then, we created an animal model of PCL-ruptured knee using the rabbit. After harvesting the PCL-ruptured knees and their control group at different designed time point, we carried out mechanical tests and histological evaluation. The mechanical tests consisted of macro-scale tensile test and micro-scale nanoindentation. We applied the maximum stress and elastic modulus obtained from tensile test and the micro-hardness and the micro elastic modulus obtained from nanoindentation as the judgment index for mechanical properties. In histological aspect, we observed the alterations on cell number, collagen organization, collagen composition and the MMPs expression.The results of the project will provide basic and fundamental experimental evidence and theoretical support for the treatment of PCL rupture. OBJECTIVE:Investigate the effect of PCL rupture on the ACL straining under different loads at different flexion positions respectively.METHOD:The straining of ACL-AMB and ACL-PLB in all12fresh normal adult knee joint specimens are tested when the knee joints loaded with200N,400N,600N,800N through the arc of flexion from0°,30°,60°to90°. Follow that, the12specimens are divided to two groups, namely, anterolateral bundle (ALB) dissected group and posteromedial bundle (PMB) dissected group randomly. Measure the straining of ACL as before. At last, completely cutting off the PCL and testing the straining as the complete dissected PCL group. Using ANOVA compare the multiple sample mean values, P<0.05is regard as the difference between values has the significance.RESULT:1.0°position:under200N,400N,600N and800N load, after PMB, ALB or PCL dissected the straining of ACL-AMB and ACL-PLB did not change significantly (P>0.05).2.30°position:under200N load, after PMB, ALB or PCL ruptured the strains of ACL-AMB and ACL-PLB did not change significantly (P>0.05); under the load of400N,600N and the800N, the compressive stains of ACL-AMB and ACL-PLB increased significantly (P<0.05). The strains of ACL-AMB and ACL-PLB among PMB dissected knees, ALB dissected knees and PCL dissected knees were not significantly different under the load of200N,400N,600N and800N (P>0.05). 3.60°position:①The strain of ACL-AMB:after PMB dissected, when under200N load, the strain of ACL-AMB did not change significantly (P>0.05); when under the load of400N,600N and800N, the compressive strain of ACL-AMB increased significantly (P<0.05). After ALB and PCL dissected, the compressive strain of ACL-AMB increased significantly under the load of200N,400N,600N and800N (P<0.05). The ACL-AMB’s compressive strains of PCL dissected knees were much larger than the PMB dissected ones under the load of200N,400N and600N (P<0.05).However, the ACL-AMB’s compressive strain of PCL dissected knee were much larger than the ALB dissected ones only under the200N load (P<0.05). Under400N and600N, the ACL-AMB’s compressive strains of ALB dissected knees were larger than the the PMB dissected ones (P<0.05).②The strain of ACL-PLB:under200N and400N load, after PMB, ALB and PCL dissected, the strains of ACL-PLB did not change significantly (P>0.05); under600N and800N load, the compressive stains of ACL-PLB increased significantly (P<0.05). The ACL-PLB’s compressive strains of PCL completely dissected knees were much larger than the PMB dissected ones under the load of600N and800N (P<0.05). However, the ACL-PLB’s compressive strains of ALB dissected knees were not significant different with the ones of PCL dissected knees under the load of200N,400N,600N and800N (P>0.05). Under600N and800N, the ACL-PLB’s compressive strains of ALB dissected knees were larger than that of the PMB dissected knees (P<0.05).4.90°position:①The strain of ACL-AMB:under200N,400N, 600N and800N, after PMB, ALB and PCL dissected, the compressive strains of ACL-AMB increased significantly (P<0.05). The ACL-AMB’s compressive strains of PCL completely dissected knees were much larger than the PMB dissected ones only under the load of200N (P<0.05). The ACL-AMB’s compressive strains of ALB dissected knees were not significant different with the ones of PCL dissected knees under the load of200N,400N,600N and800N (P>0.05). Under200N and400N, the ACL-AMB’s compressive strains of ALB dissected knees were larger than that of the PMB dissected knees (P<0.05), when under600N and800N, the differences between the two groups were not significant (P>0.05).②The strain of ACL-PLB:under200N,400N,600N and800N, after PMB, ALB and PCL dissected, the compressive strains of ACL-AMB increased significantly (P<0.05). The strains of ACL-PLB among PMB dissected knees, ALB dissected knees and PCL dissected knees were not significantly different under the load of200N,400N,600N and800N (P>0.05).CONCLUSION:1. When the knee located at the0°position, PMB dissected, ALB dissected and PCL complete dissected all play little influence on the biomechanical behavior of the ACL.2. When the knee located at the30°position, under the load of200N, PMB dissected, ALB dissected and PCL complete dissected all play little influence on the biomechanical behavior of the ACL. However, when under the load of400N,600N and800N, the ACL underwent compressive strain and the tensile stress applied on ACL decreased, which made the ACL relax than normal situation.3. When the knee located at the60°and90°position, except several situations, PMB dissected, ALB dissected and PCL complete dissected all play significant influence on the biomechanical behavior of the ACL. The ACL underwent compressive strain and the tensile stress applied on ACL decreased, which made the ACL relax than normal situation.4. PMB and ALB collaborate during the flexion of the knee. Their functions together compose of the whole function of PCL OBJECTIVE:Investigate the effect of PCL rupture on the mechanical properties of ACL in an animal model.METHOD:Randomly distribute the two knees of48male adult rabbits into experiment group and control group. The experiment side underwent PCL dissected while control side kept PCL intact. The8th,16th,24th and40thweek after operation were chosen as the sample harvested time points. Sacrifice12rabbits randomly at each time point. Then,6samples underwent tensile test to obtain the macro mechanical properties as maximum stress and elastic modulus, other6samples were carried out nanoindentation for micro index as micro hardness and micro elastic modulus. T-test was used to compare the sample mean values, P<0.05is regard as the difference between values has the significance.RESULT:1. At the8th,16th,24th and40th week after operation, there were no significant differences on the aspects of length and cross section area between the ACL from experimental and control group (P>0.05).2. At the8th and16th week after operation, there were no significant differences on the aspects of maximum stress and elastic modulus between the ACL from experimental and control group (P>0.05).However, at the24th and40th week after operation, both the maximum stress and elastic modulus of the ACL from experimental group decreased significantly compared with the ACL from control group (P<0.05). 3. At the8th and16th week after operation, there were no significant differences on the aspects of micro hardness and micro elastic modulus between the ACL from experimental and control group (P>0.05).However, at the24th and40th week after operation, both micro hardness and micro elastic modulus of the ACL from experimental group decreased significantly compared with the ACL from control group (P<0.05).4. The tendency of alterations on the mechanical properties were coincident between the macro-scale and micro-scale mechanical tests.CONCLUSION:1. After the PCL ruptured, in the40-week’s experimental period, there were no significant changes on the length and cross section area of rabbit ACL.2. After the PCL ruptured, the mechanical properties of rabbit ACL were changed. The tensile strength of ACL deteriorated.3. The results obtained from nanoindentation is consistent with the traditional tensile test. Thus, nanoindentation could be applied in the micro mechanical test in soft tissue. OBJECTIVE:Investigate the effect of PCL rupture on the histology of ACL in an animal modelMETHOD:Randomly distribute the two knees of24male adult rabbits into experiment group and control group. The experiment side underwent PCL dissected while control side kept PCL intact. The8th,16th,24th and40thweek after operation were chosen as the sample harvested time points. Sacrifice6rabbits randomly at each time point. The samples underwent histological evaluation to see the alterations on cell number, cell morphology, collagen fiber structure, fiber arrangement and collagen composition. At last, we applied immunohistochemistry method to detect the expression of MMP-1and TIMP-1in ACL. T-test was used to compare the sample mean values, P<0.05is regard as the difference between values has the significance.RESULT:1. Morphology observation:At the8th,16th and24th week, there were no significant differences of the ACL morphology between experimental group and control group; at the40th week, the ACL of experimental group become slightly yellow, gloomy and soft.2. HE stain observation:At the8th and16th, there were no significant differences between experimental group and control group; at the24th and40th week, the cell number of experimental group decreased (P<0.05); and the cell nuclei become round, the fiber loss the parallel arrangement and the normal structure deteriorated in the experimental group. 3. Transmission electron microscopy observation:At the8th and16th, there were no significant differences between experimental group and control group; at the24th and40th week, the collagen fiber diameter became bipolar distribution with the occurrence of thin and thick fiber. The collagen fibers in the experimental group arranged in sparse, the gaps between fibers increased, and more thin fibers emerged.4. Sirius-red stain and polarized light microscopy observation:At the8th,16th and24th week, there were no significant differences of the type Ⅰ collagen content between experimental group and control group (P>0.05); at the40th week, the type Ⅰ collagen content in ACL of experimental group was significantly reduced compare with the control group(P<0.05). At the8th and16th week, there were no significant differences of the type Ⅲ collagen content between experimental group and control group (P>0.05); at the24th and40th week, the type Ⅲ collagen content in the ACL of experimental group was significantly increased compare with the control group (P<0.05). At the8th and16th week, there were no significant differences of the type Ⅰ/Ⅲ collagen content ratio between experimental group and control group (P>0.05); at the24th and40th week, the type Ⅰ/Ⅲ collagen content ratio in the ACL of experimental group was significantly decreased compare with the control group (P<0.05).5. Immunohistochemistry observation:At the8th week, there were no significant differences of the MMP-1expression between experimental group and control group (P>0.05); at the16th,24th and40th week, the MMP-1expression in ACL of experimental group was significantly increased compare with the control group(P<0.05). At the8th,16th and40th week, there were no significant differences of the TIMP-1expression between experimental group and control group (P>0.05); at the24th week, the TIMP-1expression in the ACL of experimental group was significantly increased compare with the control group (P<0.05).CONCLUSION:1. After the PCL ruptured, the histological alteration occurred a certain time later. The cell number decreased while the collagen fibers became disorganized and sparse, the gaps between fibers broaden. Moreover, the collagen composition, such as the content of the type Ⅰ collagen and type Ⅲ collagen changed during this procedure.2. After the PCL ruptured, the abnormal expression of MMP-1and TIMP-1in the ACL may be one of the reasons that mediate the histological alterations of ACL. |
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