| BackgroundAnterior cruciate ligament (ACL) injury is the most common ligament injury in knee joint. After injury, the ACL reconstruction under arthroscopy is the most common treatment. Although the treatment was applied widely, the rate of failure and revision after surgery was still high as10-15%. The accuracy of position for ACL tunnel affected the clinical result. Compare with traditional treatment, the computer assisted surgery (CAS) for ACL reconstruction which developed these years could improved the accuracy of tunnel, reduced the impingement rate of ACL graft and get better clinic effect.After ACL reconstruction, there is still high occurence rate of osteoarthritis in these patients, the probable cause is the abnormal stress on cartilage which exceed the normal range of stress in cartilage of knee joint, and may resulted in the degeneration or even wear or destroy of cartilage and meniscus. So, it is important to choose the best project of ACL reconstruction which can result in the most proper stress of cartilage after surgery. The3-dimensional finite element model of knee joint can simulate the different conditions of motion and force in knee joint, analyzed the biomechanical property of the ligament and cartilage in knee joint with different conditions precisvely. It is helpful for fully understanding the causes of the osteoarthritis and the biomechanical property and injury mechanics of major ligaments and cartilage in knee, and helpful for exploring the most proper method of ACL reconstruction, diagnosis and assessment method on related disorders injuries of ligaments and cartilage and surgical procedures of ACL reconstruction.Objective1. Based on the CT and MRI data of a healthy subject’s bilateral knees, to invent the innovated CAS system which was advanced domestically for ACL reconstruction, it could design the virtual plan of ACL reconstruction.2. Applied the innovated CAS system-ACL detector in clinic for ACL reconstruction, compare with traditional ACL reconstruction, to explore the effect and advantage of CAS system for ACL reconstruction, establish the3D model of knee joint after ACL reconstruction and analyzed the position and impingement of ACL graft.3.In order to explore the causes of osteoarthritis after ACL reconstruction and find the optimal ACL reconstruction method which can result in the most suitable biomechanical condition of cartilage, it is neccerary to establish the3D finite element model of normal and postoperative knee joint with different ACL reconstruction methods, simulated the different flexion conditions and forces of knee joint, and analyzed the different stress conditions of ACL, cartilage in femur, tibia and meniscus.Methods1. Based on the successful experiences of establishing the3D model of knee joint at past, a healthy person was selected as a subject, whose bilateral knee received1.5T MRI at extensive position and256row CT scan at flexed position of90°, imported the MRI and CT data into the3D reconstructive software MIMICS14.11and Geomagic Studio2012to established the3D model of bilateral knees, then, imported the3D model of knee into the innovated CAS system-ACL Detector, it could designed the virtual plan of ACL reconstruction.2. In order to explore the feasibility, effect and advantage of innovated CAS system-ACL detector, we applied the CAS system in clinic. From March2009to October2012,80cases of ACL reconstruction surgery were finished. All the cases were diagnosed as ACL injury by physical examination and MRI. All the patients were divided into2groups, Computerized assisted group (CAS group) of patients (40cases) received ACL reconstruction assisted by the viutual plan of ACL detector; Traditional surgery group (TS group) of patients (40cases) with ACL injury received traditional ACL reconstruction. At18months after surgery, the surgical effect of2 groups were evaluated by knee stability test and subjective functional score, the digital3D model of postoperative knees were estabilished based on MRI and CT date and evaluated the position and impingement condition of ACL graft, the results were analyzed statistically.3.6healthy man (Normal group) and12patients (6cases in CAS group and6cases in TS group) were selected as subjects for finite element study, the healthy man’s bilateral knee and the patients’operated knee s were scanned by1.5T MRI, imported MRI data of all subjects into the software such as MIMICS14.11, Geomagic Studio2012and ABAQUS6.10to establish3D finite element model (FEM) of knees, the FEM consisting of two bony structures, articular layers, menisci, and four principal ligaments. After verified the validity of the FEMs by comparing other FEM studies, added134N posterior femoral force and350N vertical force on the3D finite element model respectively at flexed angle of0°,30°,60°,90°, Analyzed the stress of ACL, cartilage and meniscucs of knee joint, Then, Compared the magnitude and distribution of stress in ACL, cartilage and meniscus among3groups. The statistical standard was α=0.05.Results1. The computerized assisted system-ACL detector was invented, it was advanced domesticlly. It could designed the virtual plan of ACL reconstruction based on subjects’MRI and CT date in knee joints, the virtual plan included the reconstruction tunnel’s position, angle of ACL graft, the entrance and exit of virtual tunnel in femur and tibia and the proportion of graft’s attachment.2.After applied the ACL detector in clinic, all cases in CAS and TS groups were followed up by12-24months (mean,18months), all the incisions healed well, and no complication was found. The results indicated that there was no significant difference in negative rate of lachman test (P>0.05) and pivot shift test (P>0.05) between two groups after surgery. After surgery, the CAS group’s Lysholm score improved from47.83±5.14to93.28±3.34,(P<0.05), the IKDC score improved from42.25±4.46to89.13±3.45,(P<0.05); The TS group’s Lysholm score improved from46.85±7.23to 92.05±3.27,(P<0.05), the IKDC score improved from42.73±4.82to88.03±3.25,(P <0.05). There was no significant difference in Lysholm and IKDC score after surgery between2group,(P>0.05). The3D models of operated knee were established succsefully and the position, angle and impingement of ACL graft could be observed. The results of ACL graft impingement measurement indicated that there was significant difference in Impingement rate of ACL in3D model,1case (2.50%) in CAS group and8cases (20.00%) in TS group,(P<0.05) between2groups after surgery.3. The3D finite element models (FEM) of healthy and operated knee were established successfully, the models consisting of femur, tibia, articular layers, meniscus, ACL, posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LCL). After verified the validation of the FEM of each groups, applied posterior femoral134N force on femur at different flexion angle, there was no sigficant difference in stress of ACL among3groups (P>0.05). After applied350N vertical force on femur at different flexion angle, the stresses in most part of cartilage and meniscus of TS group were higher than CAS group and control group (P<0.05). There was no significant difference (P>0.05) in stresses of all parts in knee joint between CAS group and control group.Conclusion1. The innovated computer-assisted surgery system for ACL reconstruction-ACL detector which was advanced domestically was invented. It could designed the viutual plan for ACL reconstruction and could be applied in clinic succesufully. After applied the computer-assisted surgery technology in clinic, it could improve the function of knee, compared with traditional ACL surgery,it could reduce the impingement rate indicated the better effect of CAS technology.2. Established the3D finite element model of normal and operated knee joint after ACL reconstruction successfully, The stress in cartilage of femur, tibia, meniscus and ligaments in knee joint could be effectively analyzed.3. There was no significant difference on stress of ACL among3groups after ACL reconstruction. The stress on cartilage of femur, tibia and meniscus of CAS group were similar to normal group, and lower than some part of cartilage in CS group. Indicated the causes of complications after traditional ACL reconstruction and the advantages of CAS technology.. |
