| 【Background】The most common sports sprain of the knee joint is the rupture of the Anterior Cruciate Ligament(ACL).Autologous hamstring tendon as a graft to reconstruct ACL is the mainstream treatment for anterior cruciate ligament injury in recent years.With the specification and improvement of the arthroscopy technique of the clinician,the failure of reconstructing the anterior cruciate ligament graft can be avoided as much as possible by prescribing the standardized surgical plan and the intraoperative specification.By adjusting the patient’s lifestyle,the chances of re-injury can also be reduced.However,there are still 5% to 16% of patients with graft failure underwent revision surgery,the recurrence rate of 3% to 19% damage after surgery.These reasons are closely related to the causes of re-injury and surgical techniques and the poor biological ligamentization.A series of changes in biological and mechanical properties occurring in the joint cavity after surgery and the process of transforming the tendon graft into a histological structure similar to that of the natural anterior cruciate ligament is defined as ACL graft remodeling or ligamentization.The process of tendon ligamentation is divided into four stages: early stage,remodeling stage,stable stage(mature stage and quiescent stage).The process of tendon graft transforming from tendon tissue to natural ACL tissue during remodeling is elaborated.Generally,about 18 months after the surgery,the graft enters the plastic stabilization stage,namely the tissue maturity stage,at which time the histological structure of the tendon graft has no visible change.Well-formed grafts have high biomechanical strength,and poorly shaped grafts have poor biomechanical strength.Furthermore,it affects the recovery of knee joint stability and motor function in postoperative patients,and the biological and mechanical properties of the affected ligament are directly related to the remodeling results.The postoperative magnetic resonance imaging(MRI)and arthroscopic reexamination were generally reliable diagnostic criteria for imaging and morphology,but the ultimate outcome of the graft was determined by the histologicalcharacteristics of the graft at the time of plastic stabilization.A large number of animal experiments and a small number of human experiments have studied the histological evolution of graft remodeling(ligamentization).It is believed that the graft can survive at all stages of remodeling,and finally can be transformed into a histologically similar natural ACL structure,but The ultrastructural features such as the diameter and distribution of collagen fibers are still quite different from those of natural ACL.At present,most of the cytology,histology and biomechanics of grafts have been studied in each remodeling stage from a longitudinal time span.There are few lateral comparison studies of histology of ACL grafts in a stable period.In this study,according to the criteria of nuclear magnetic resonance imaging of transplants,patients with good and poor remodeling after ACL reconstruction(spinning stable period)were selected.Two kinds of patients were subjected to secondary arthroscopic exploration and analyzed by histology.To explore and summarize the histological features of grafts with different scoring results after reconstruction of ACL.【Objective】To explore the histomorphological features of stable plastic grafts after reconstruction of the anterior cruciate ligament(ACL)with autologous hamstring tendon transplantation.The differences in the expression of type I and type III collagen in different remodeling grafts were observed.【Methods】Eighteen patients with anterior cruciate ligament injuries were selected as subjects,who were operated with autogenous hamstring tendon transplantation for single-bundle reconstruction of ACL for 4 years or more after surgery,who needed to be treated with tibial end internal fixation for removal and underwent arthroscopic exploration of the tendon again.Most cases of loss,re-fracture and obvious relaxation of MRI and arthroscopic implant were excluded.Arthroscopic scoring was conducted according to the graft blood vessel and synovial coverage,graft tension and graft volume,and patients with good or poor graft remodeling after ACL reconstruction(remodeling stability period)were screened out.Tissueof about 3 mm(thick)8 mm(long)in the center of the body was clamped by basket forceps,and histological examination was performed under an optical microscope,transmission electron microscope,type I and type III collagen immunohistochemistry,COL1A1 and COL3A1 real-time fluorescence quantitative PCR(real-time PCR)examination was performed respectively.Another 9 natural ACL specimens were taken as the control group,and the samples were taken from patients younger than 60 years old who underwent total knee replacement surgery.Evaluation indexes under a light microscope: cell morphology,graft revascularization.The anabolism level,fiber type and distribution of collagen were evaluated under an electron microscope.Histological scores of the three groups were compared.【Results】Eighteen ACL reconstruction cases(48 ~ 122 months after surgery,an average of 82.3 months)and 9 natural ACL specimens were included in this study.Results of secondary arthroscopy: GRG in 11 cases and PRG in 7 cases.Observation results under a light microscope: histological characteristics of GRG specimens a under light microscope were similar to natural ACL,showing as follows: few blood vessels were distributed,collagen fibers were tightly bunched and evenly arranged,the nuclei were mainly linear or fusiform,and oval and round shapes were rare.Under light microscope,PRG specimens showed a large number of inflammatory hyperplasia vessels,loose arrangement of collagen fibers,oval or round nuclear morphology,and rare linear and spindle shapes.PRG light microscope score was significantly lower than that of the other two groups,with statistically significant difference(P < 0.05).There was no significant difference in light microscope score between GRG and control group(P > 0.05).Under the electron microscope results comparison: similar to natural ACL,all the reconstruction of the ACL graft collagen fibers are characterized by large diameter(100 nm)or higher and small diameter bimodal pattern.But PRG specimens,small diameter collagen fiber ratio than natural ACL and GRG decreased significantly,and cells anabolic level significantly higher than other two groups,the significant difference(P < 0.05).Compared with the control group,there was no significant difference in the score ofGRG at the anabolic level between the two groups(P > 0.05),but the distribution score of GRG collagen fibers was still lower than that of the natural ACL,which was statistically significant(P < 0.05).Immunohistochemical results: the collagen fibers in the control group(natural ACL)and GRG specimens were mostly type I and type III,and the fibers were arranged neatly.However,in PRG tissue samples,the collagen fibers of type I and type III in the graft were significantly reduced and arranged relatively irregularly.The immunohistochemical score of PRG specimen was significantly lower than that of GRG specimen and natural ACL,which was statistically significant(P < 0.05).Rt-PCR results showed that the expressions of COL1A1 and COL3A1 in PRG specimens were significantly lower than those of GRG and natural ACL,and the relative expressions were statistically different(P < 0.05).【Conclusion】After the graft enters the stable period of remodeling,the well-shaped graft is compared with the poorly shaped graft,the graft collagen content is rich,remodeling good fibers arranged orderly,collagen fibers bulky,abundant organelles,cytoplasm nuclear scale big,the synthesis of collagen metabolism,collagen fiber distribution and expression of anterior cruciate ligament,more close to the natural histological structure characteristics are similar to natural ACL,but there still is significant difference with natural ACL. |
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