A Histological And Biomechanical Study Of The Integration At The Tendon-bone Interface After Reconstruction Of The Anterior Cruciate Ligament In Dogs

1Objective Combine with histological and biomechanical study toobserve the growing condition of tendon-bone surface，knowledge of thehealing process will lead to a better under-standing of how to improve theinitial fixation of graft to bone，and aid in the decision of when to remove aninternal fixation device that has been used for the attachment of a graft．Italso can aid in the identification of methods to improve the biologicalhealing response of tendon grafts， In addition, the findings of the currentstudy can help clinicians in the planning of early weight-bearing orrange-of-motion rehabilitation modalities. The results of the study would beused as guidance of the clinical appliance．2Materials and metheods2.1Experimental Animal and Model of the reconstruction of theanterior cruciate ligament Selecting36beagle dogs，healthy，male，bodyweight12.5±1.48kg,The tendon of the flexor digitorum longus (8cmin length) was harvested, the tendon was then folded in half to create a4-cm-long double-stranded graft.2.2Randomization36beagle dogs were divided into two Groups by computer at random，18per group. Both histological sections group andbiomechanics research group are18beagle dogs (18knees).2.3Specimen management At the two, four, six， eight， ten,andtwelve-week time-periods, The dogs were sacrificed by steps．Five animalswere killed at each of the five time-periods. Take knee joint (includingfemoral and anterior cruciate ligament), respectively, were randomlyselected3knees do biomechanical pull-out test, and the other3kneespecimens were fixed, decalcified, take the tendon bone interface slice,staining.3Result3.1Histological findingsEarly in the healing process, the first2weeks, the tendon-bone interfacetissue in cellularity and vascularity, with formation of osteoblasts, chondriodcells and fibroblasts, around the bone tunnel wall. Bone growth factors,such as of BMPs abundantly expressed and seen in the bone tunnel wall nearthe small amount of newly formed bone trabeculae. Fibrovascular interfacetissue intensive postoperative approximately4weeks, and arranged in order,followed by a gradual decrease, associated with type II collagen depositionof chondriod cells from bone growth to the tendon. Tendons around the newbone formation, bone tunnel wall thickening. However, during this period,the collagen fibers machine is not sufficient, tendon continuity of bone can only occasionally be seen. Later, at6weeks, the collagen fibers grow tomaturity, the continuity of the tendon bone reconstruction.8weeks aftersurgery, the vertical arrangement of Sharpey-like fibers in the tendon boneinterface center visible. Sharpey-like fibers of type III collagen and tendonsconnect bone transplant, is considered tendon osseointegration earliest signs.Early biomechanical results is also considered together of collagen fibers incontinuity with the tendon osseointegration. The early tendon bone healingalmost depends on the the bone tunnel biology or biomechanicalenvironment. After8-12weeks, the tendon bone healing process to enter aperiod of chronic inflammatory reaction, the tendon bone healing hasgradually in a stable.3.2biomechanics research group2,4,6, and8weeks after surgery, the tendon can be pulled out from thebone tunnel, tendon pull-out force is growing, and with time, from10weeksto the twelve time-periods, all specimens had failed by pull-out of thetendon from the clamp or by mid-substance rupture of the tendon.4ConclusionsAutologous tendon reconstruction of the anterior cruciate ligament earlyhealing of the tendon-bone interface experienced acute inflammation,ischemic necrosis of the period, collagen fibers reconstruction and chronicinflammation，later beginning to stable. During this healing of tendon bone interface strength is weak, until the eighth week, the only relatively strongactivity during this exercise should not be excessive. during this therehabilitation of the forces and movements should also after8weeks, inorder to avoid tendon relaxation and loose, recommended internal fixationand extraction time should be more than12weeks.