Establisment Of Rotator Cuff Injury Repair Model In Canine

Background & ObjectiveRotator cuff tears are a common disease result in shoulder pain and disability,reduce function,but the repair failure rates ranged from 20% to 90%,even worse the treatment of large or massive rotator cuff tears is a big challenging because the failure rates as high as 94% reported in many studies,large or massive rotator cuff tears may not be repairable relied on the present surgical management.Thus, new therapeutic strategies need to be developed to provide effective mechanical reinforcement of the repair.animal shoulder models are used to systematically investigate the factors influencing rotator cuff injury and repair to help to find out the most effective strategies,rotator cuff injury and repair has been investigated in rat, rabbit,sheep and dog. but each model has more or less defect and most animals are quadrupedal with weight bearing forelimbs,in order to simulate the clinical rotator cuff injury and repair as much as possible so we design this study,in this study evaluated the utility of the canine model for studies of using autologous semitendinosus to repair acute large or small full-thickness rotator cuff tendon injury. There have many research using canine model to investigate various repair methods for rotator cuff tears.but there have a defection that can’t be ignored.that’s because although the dog injured shoulder joint have be repair but the repaired shoulder haven’t be protect as clinical.in order to solve this problem we using an external fixation device to prevent the movement of injured shoulder joint.and many studies reported used various bioscaffolds(such as AMD、SSI) as an enhancement patch to repair the injury rotator cuff,but the effect couldn’t be satisfactory.we consider the reason may be the body’s immune graft rejection and the biomechanical strength of bioscaffolds is not enough.to improve it we think the autologous semitendinosus seems to be an ideal scaffold.and autologous semitendinosus have been mature used for the reconstruction of cruciate ligament in clinical.In this study we using autologous semitendinosus expansion patch repair rotator cuff injury in canine immobilization model to evaluate the effect by gross observation^ biomechanical test and hematoxylin and eosin staining.MethodsWe randomly assigned 12 male beagle dogs weighing between 20 and 30kg (estimated age 1-2 ye) to 3 equal groups.Preoperative analgesics and antibiotics were administered to all dogs.after surgical area preparation, about a 7-9-cm incision was made at the right shoulder.the infraspinatus muscle and tendon were isolated. And the tendon was sharply transected from the greater tuberosity of the humerus.Debridement was performed at greater tuberosity to make sure the soft tissues was complete removed.In group 1 infraspinatus tendon were detached from the greater tuberosity as acute small rotator cuff tear.and using a 1.0 Kirschner wire drilled two holes at greater tuberosity.via modified Mason-Allen suture to repair the infraspinatus(线).Once repair was accomplished. suture incision immediately.two pin external fixation were fixed at middle part of humerus and ulna.place the elbow flexion at 90 degree.then install connecting rod and tightening screws.In group 2 infraspinatus tendon were detached from the greater tuberosity,then make a gap about 4 mm in the anterior-to-posterior and 5 mm in the medial-to-lateral dimension at the end of infraspinatus tendon as a simulation of acute large rotator cuff injury group,repair infraspinatus,close incision and install external fixation as the same as group 1.In group3 infraspinatus tendon were treated like group two.we get the semitendinosus from the other side of the thigh and debride muscle tissue,then exten the scale to 10mm*30mm as a patch augmentation for rotator cuff repair;close incision and install external fixation as the same as group 1.(Table.1)All dogs were used external fixation device to fix the elbow joint in the 90 degree flexion position to avoid weight-bearing, postoperation, the dogs were placed in recovery room for 24hours of intensive care and then allowed free activity in a large separate cage,then Flurbiprofen 4 mg/kg subcutaneously daily for 1 week postoperatively, injected penicillin 80 million units(day for three days).obseved till 6-weeks after surgery to make sure the external fixation device haven’t loosed.and at 6 weeks after surgery, the dogs were euthanized with air embolism death through the leg veins.specimens were harvested from the repaired shoulders, including proximal humerus, and infraspinatus tendon.each infraspinatus muscle-tendon complex was frozen at -80℃ and stored until biomechanical testing and histologic evaluation were performed.Gross observationEach infraspinatus muscle-tendon complex was assessment of the integrity of the tendon insertion site,all shoulders were assessed for gross differences between the groups.Biomechanical testingThe muscle part of each infraspinatus muscle-tendon complex were quick-frozen using dry ice and perform biomechanical testing with a conventional tensile tester.Each repaired rotator cuff specimen was tested the ultimate force-to-failure under displacement control at a rate of 0.5 mm/sec. Load and actuator displacement were recorded at a sample rate of 50 Hz.Maximum load was defined as the peak force.Histologic evaluationAfter biomechanical testing all Specimens were fixed with 4% paraformaldehyde for 24 hours at 4℃. Samples were then decalcified by incubation in an ethylenediaminetetraacetic acid (EDTA) solution (pH 7.5) for 4 weeks at room temperature.followed by gradient replacement with 20% sucrose for 24 hours at 4℃. Tissue blocks were embedded in an OTC compound (Sakura Seiki, Tokyo, Japan) and quick-frozen using dry ice. Serial sagittal sections (20 mm thick) were cut parallel to the long axis of the supraspinatustendonusinga cryostat (Jung CM3000; Leica, Wetzlar.Germany) and each section was fixed on a glass slide..The infraspinatus tendon tissue were transected from greater tuberosity make masson staining to evaluate cell morphology and proliferation.ResultsGross observationAt 6 weeks after rotator cuff repaired there was complete tissue bridging in all groups.but there have same different among the three groups:in group one although there are full of tissue at the surface of tendon-to-bone while the withe scar tissue was more than the normal tendon tissue;and we observed that the tendon retracted in group two and there haven’t obvious tendon tissue;in group three using the autologous semitendinosus expansion patch repair group.although infraspinatus tendon shape is deformed and covered with white scar tissue, but the general direction and tendon texture can still observed.Biomechanical testResults show that in the same huge rotator cuff injury group for the final load test,with autogenous semitendinosus expansion repair group can afford better than without using autogenous semitendinosus expansion repair group.Masson stainingAll experimental canine infraspinatus tendon check point Masson staining showed that (*20), acute rotator cuff injury group (Figure 13) tendon fibers arranged roughly normal; massive rotator cuff injury group (Figure 14) tendon fibers arranged in disorder, and the number of tendon cells significantly below those in the former group; semitendinosus muscle repair group (Figure 15) staining showed that not only the tendon fibers arranged in neat but also more cell number compare with massive rotator cuff injury group.Conclusion1. By using external fixator to repair canine shoulder joint can effectively avoid the external factors of the influence of rotator cuff repair, close to the ideal animal model, for a variety of shoulder cuff repair materials and surgical methods to collect more accurate experimental data.2. On the basis of this animal model, the use of autologous muscle tendon repair of the expansion of the study found that the use of autologous tendon bone healing can promote tendon bone healing to achieve a reliable biomechanical strength.3. On the basis of this animal model, the use of autologous expanded part of the Achilles tendon repair study found that the use of autologous muscle tendon expansion can effectively promote the proliferation of tendon cells.