Establishment Of The Infraspinatus Insertion Injury And Healing Animal Model In Dogs And Its Preliminary Histological And Biomechanical Study

ObjectiveTo establish an animal model of infraspinatus insertion injury in canine and to investigate the feasibility of this canine model followed by the histological and biomechanical study on the tendon bone interface. It is can also play an important role in tendon repair rmaterials research in next step. MethodEstablishment of the insertion of infraspinatus injury and healing animal model : Infraspinatus insertion of twenty-seven adult beagles(13.6-16.2 kg) were released and repaired. Tendons of the infraspinatus were repaired via transosseous bone tunnels.Experimental design: The canines were randomly divided into three groups:control group,experimental group 1 and experimental group 2.Each group has nine beagles.All of dogs were repaired after tenotomy immediately. Experimental group were repaired after tenotomy with elbow fixation in order to promote healing for reconstruction of infraspinatus bone-tendon junction in a no tension environment. Control group were repaired after tenotomy without e lbow fixation.Sample collecting and making:The control group and the experimental group 1 were sacrificed at 6 weeks postoperatively. The experimental group 2 were sacrificed at 8 weeks postoperatively. We harvested the specimens, including the infraspinatus and the proximal humerus and respectively selected three specimens from the experimental group 1, group 2 and control group. The three specimens and a blank contrast specimen of shoulder joint were fixed, decalcified, sliced and observed by hematoxylin-eosin and Masson staining. The rest of the specimens for the biomechanical testing were assessed at the same time. ResultHistologic observation and results: We found a large number of cell proliferation, hyperplasia of collagen tissues arranged orderly in dense tendon- bone interface six weeks after surgery in the experimental group 1.The continuity of tendon-bone has been rebuilt.Tendon bone healing has gradually stabilized at this time. There were no obvious differences been found between the experimental group 2 and experimental group 1 eight weeks after surgery.The main performance is the cell hyperplasia.The collagen fibers were arranged orderly. These were good signs about tendon bone healing.While in the control group,we did not find these performance.Instead. The arrangement of collagen fibers were disordered. A large number of scar tissues can be found.Biomechanics research results: Comparing the experimental gro up 1, 2, to the control group,there were significant difference among the ultimate load, stiffness and cross-sectional area of muscle tendon and tendon retraction distance.Comparing the experimental group 1 and group 2, there were no significant difference among the ultimate load, stiffness and cross-sectional area of muscle tendon and tendon retraction distance. ConclusionThe canine model designed in this study is simple and repeatable.The experimental group build new insertions of the infraspinatus six weeks after surgery. The opposite results occur in the control group. Tendon retract dramatically and there are no obvious insertions of the infraspinatus.A lot of scar can be found around the tendon bone interface. The abnormal proliferation of the tendon aro und insertions of the infraspinatus is highly significant and its cross-sectional area are increased.The ultimate load and stiffness are significantly higer in experimental group than in control group.Using external fixation bracket of elbow in the animal models is a simple and effective method and can significantly improve the success rate of the rotator cuff injury in canine animal model.It can aslo be more similar with the normal physiological healing process.This method can be used as a conventional so lutions of rotator cuff injury canine animal model.