||Mechanical Property of LARS Artificial Ligament after Tissue Ingrowth
||Institute of Biomedical Engineering
LARS artificial ligament
anterior cruciate ligament
LARS (Ligament Augmentation and Reconstruction System) artificial ligament was used as reconstructive material for ruptured anterior cruciate ligament since 1980’s. Orthopaedics and biomedical engineers expected that soft tissue, which was similar to the connective tissue of human ligament, grew into the implanted artificial ligaments after reconstructive procedures to replace the gradually fatigued material of artificial ligament as the time going. Several groups have confirmed that soft tissue grew into the implanted artificial ligament according their study. Some others also confirmed that the PET fibres and fibrous cells had good biocompatibility in their study. They also found the fibrous cells reproduced between the PET fibres. Guidoin et al concluded soft tissue ingrowth of artificial ligament decreased the strength because that integrity of artificial ligament was destructed according to the explanted artificial ligaments which took from the failure clinical cases. They did not agree to the positive effect after soft tissue ingrowth in implanted artificial ligament. According to the experimental results, Poddevin et al concluded that soft tissue ingrowth of artificial ligament decrease the friction of fibres. Therefore, the effect was positive. Up to now the influence of the soft tissue ingrowth of implanted artificial ligament on the mechanical properties of the artificial ligament is uncertain. The purpose of this research was to study the mechanical property and biocompatibility after tissue ingrowth into LARS artificial ligament according to animal experiment. At the same time, in this study we analyzed the finally clinical results of 26 cases who received LARS artificial ligament reconstructive procedure for 8 – 15 years. In animal experiment, we analysed it by gross anatomy, micro-computed tomography study, ultimate extension test, scanning electric microscopy study and histopathological study. In clinical cases, we analysed it by comparison with anterior drawing displacement, Lyshom score, Tegner activity score and degenerative change of osteoarthtitis of pre-operative and post-operative and ultimate tension test of explanted LARS artificial ligament. The final inferences were according to the comparison between the animal experiment and clinical cases analysis. In this study, we adapted LARS artificial ligament. The design of this artificial ligament was different from the past other artificial ligament. The intra-articular fibres of the LARS artificial ligament are designed as unknotted free bundles of fibres set in a pre-twist 900 spiral configuration to mimic the native orientation of the ACL. This special design shall decrease the friction between fibers during movement of joint. On the other hand, the porous structure of the middle part of artificial ligament allows further fibroblastic ingrowth and accumulation of collagen fibers. There were total seven LARS artificial ligaments in this study. Five of them were fixed on the bone plate15 cm in length which kept pre-twist 900 on the middle part the artificial ligament. Two ends of knitted part of artificial ligament were enveloped by Panrose drain to prevent soft tissue ingrowth. These artificial ligaments were implanted subcutaneously in the abdomen of five mini pet pigs. The residual two artificial ligaments serve as control group. One of implanted artificial ligament slid out from the wound. We gave up this sample. After six months of implantation, four successful implants were explanted and tested including ultimate tension test, micro-computed tomography study, scanning electric microscopy study and biocompatibility study by microscopy. In addision, we analysed and compared the final results of clinical cases which received LARS artificial ligament reconstruction on Show Chwan Memorial Hospital in recent 10 years. The results of animal experiment showed that fibroblasts and collagen fibres had well grown into the unknotted middle part of the LARS. However, 12.2±2.2% of PET fibres was surrounded by foreign body giant cells in histopathological study. Force-displacement curve of four explanted LARS artificial ligaments of animal experiment exhibited similar viscoelastic character of human ligament. The tensile strength of the explanted LARS decreased by 23.53±18.04% (p < 0.001) and the elongation of the middle part of the explanted LARS increased by 69.84±38.38% (p < 0.002) in comparison with unimplanted control ligaments. There was no significant cracking or fragmentation on surface of the PET fibers by scanning electric microscopy study. We inferred that strength of PET was decreased and mechanical characters were influenced because foreign body cells around the fibers were persistently releasing potent oxidants to destruct the structure of polymer. In this clinical study, a partial rupture of artificial ligament, which took from the failure case after anterior cruciate ligament reconstruction, was analysed by ultimate tension test. The force-displacement curve of this artificial ligament exhibited similar to force-displacement curve of the explanted artificial ligament, which was grown into much of connective tissue, from the animal experiment. In other words, the force-displacement curve of this artificial ligament was significantly different from the force-displacement curve of the control artificial ligament. The ultimate strength of this artificial ligament, which took from failure clinical case, decreased significantly. Although, just a little of connective tissue grew into the bundle of PET fibres by scanning electric microscopy study. In clinical cases study, which was followed up for 8 to 15 years after artificial reconstruction, the final results revealed satisfactory. According to the results of animal experiment and clinical cases analysis, we inferred that connective tissue was able to growing into the bundles of fibres of LARS artificial ligament. Once the connective tissue grew into the bundles of artificial ligament, the artificial ligament exhibited the similar force-displacement curve as the human anterior cruciate ligament. The ultimate tension strength of this artificial ligament, which contained connective tissue, decreased significantly almost 25%. The ultimate tension strength was far more than the physiological demanding of human ligament. Therefore, it was worth to receive artificial ligament reconstruction.
TABLE OF CONTENTS
TABLE OF CONTENTS X
LIST OF TABLES XⅢ
LIST OF FIGURES XⅣ
LIST OF ABBREVIATIONS AND NOMENCLATURE XX
Chapter 1 General Introduction 1
1.1 Background 1
1.2 Gross Anatomy of the anterior cruciate ligament of the knee 3
1.3 Histology of the anterior cruciate ligament of the knee 5
1.4 Mechanical properties of the human anterior cruciate ligament 7
1.5 Literature reviews 10
1.6 General objectives 14
Chapter 2 Materials and Methods 16
2.1 Animal experiment 16
2.1.1 Materials 16
2.1.2 Methods 21
2.1.3 Postoperative care 25
2.1.4 Micro-computed tomography study 25
2.1.5 Mechanical testing 28
2.1.6 Scanning electron microscopy study 34
2.1.7 Histopathological study of the LARS artificial ligament with tissue ingrowths 35
2.1.8 Statistics 36
2.2 Clinical Cases Analysis 37
2.2.1 Patients and Methods 37
220.127.116.11 Patients 37
18.104.22.168 Operative procedure 38
22.214.171.124 Postoperative care and rehabilitation 39
126.96.36.199 Clinical assessment 40
188.8.131.52 Statistics 40
Chapter 3 Results 42
3.1 Animal Experiment 42
3.1.1 Gross observation 42
3.1.2 Micro-computed tomography study 43
3.1.3 Tensile test 46
3.1.4 Scanning electron microscopy study 51
3.1.5 Histopathological study of the LARS artificial ligament with tissue ingrowths 54
3.2 Clinical Cases Analysis 57
3.2.1 Knee Stability 61
3.2.2 Range of Motion 62
3.2.3 Knee function scores 62
Chapter 4 Discussion and Conclusion 64
4.1 Discussion of Animal experiment 64
4.2 Discussion of Clinical Cases Analysis 68
4.3 Conclusion 72
4.4 Future work 73
Appendix A: The Score of Lysholm and Gillquist for Evaluating Athletes after Knee Ligament surgery 89
Appendix B: Tegner Score of activity level 92
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