Effect Of Immobilization On Biological Character Of Anterior Cruciate Ligament Of Rabbit

Objective: Immobilization is the commonly used therapy oforthopedics, it can protect the wounded tissue; release pain and hasten thehealing. Anterior cruciate ligament is the important intra-articular part inknee that keep the knee stabilized, and it also is the vulnerability part.There have been some reports of the effect of immobilization onarticulation: such as change of articular cartilage; joint stiffness;osteoarthritis; alteration of metabolism of meniscus, and so on. But nowthere are few reports of the research of cruciate ligament. We successfullyset up a New Zealand rabbit model so as to study the effect of knee jointimmobilization on anterior cruciate ligament better, and so that we canmake use of the therapy better in clinic and obtain more satisfied result.Methods: Thirty-two New Zealand rabbit are used in this study.Twenty-four of them are selected randomly for experiment group, andone of their hind leg are immobilized randomly by long leg plaster cast,the other one is the opposite side comparison group. The remaining eightrabbit are normal comparison group. Eight New Zealand rabbit areexecuted euthanasia after immobilized for 6 weeks, 8weeks and 8 weeksplus 2 weeks active movement of remobilization. We observe thealteration of the biological character of anterior cruciate ligament in theanatomy and morphology,biomechanics and histological section. Result:1. Morphology measurement: The length and cross section area ofthe ACL of the rabbit after immobilized for 6 weeks, 8 weeks and 8weeks plus 2 weeks active movement of remobilization have changed, butcompared to the normal group and the opposite comparison group, thereis no statistic significant difference(p＞0.05).2. Biomechanical tensile test: The max load,max tension length andthe max stress,max strain,elastic modulus of the ACL of the experimentgroup are all decreased compared to the normal group and the oppositecomparison group, and there is statistic significant difference (p＜0.05).The rate of the stress relaxation and creep have also changed, and there isstatistic significant difference (p＜0.05),that is mean the biomechanicalcharacter and the material nature of the ACL have changed.3. Histological section stain: The histological sections of the ACLare stained with Haematoxylin and Eosin. The appearance of the sectionof the experiment group is that the quantity of fibroblast is significantlydecreased, the shape of the cell and nuclei have changed, the nucleipyknotic and necrosis. Collagen fibers are arranged disorderly and edema.Conclusions:1. Immobilization will not induce the change of the length and thecross section area of the ACL of the rabbit knee joint;2. Immobilization will decrease the max load, max tension length and the max stress, max strain, elastic modulus of the ACL compared tothe normal group; The rate of stress relaxation and creep has changed too,indicating the change of the ACL material property;3. Immobilization can cause the histological alteration, it ischaracterized in the significant decrease of the quantity of fibroblast,change of shape and disorderly arrangement of the collagen fibers.4. The biological character and the material property of ACL can notrecover to the normal level after 2 weeks remobilization.