| [Background]As the largest weight-bearing joints in human body, knee joint is predilection site of bone tumors, with the active proliferation in epiphyseal plate. According to some statistics, bone tumors which occurred around knee joint,15.7% account for 30% of all kinds of bone tumor and tumor-like lesions, distal femur tumors account for 15.7%. The clinical manifestation of distal femur is bone destruction. Biomechanical properties of bone could be influenced by the range of lesion which could induce pathological fracture. Therefore, how to accurately quantify the risk of pathological fracture and estimate the operation indication in terms of biomechanics is very important to clinician at home and abroad and perplexed them.Wide excision, combined with bone defect revascularization is main surgery method faced to large-scale aggressive and malignant tumors. Common styles of reconstruction include autogenous bone graft or allograft, tumor prosthesis replacement, replantation of inactivated tumor bone. autogenous bone graft is considered the gold standard for treatment of bone repair, however, its application is limited because of limitation of bone source and potential infection or pain in donor site. Allograft also has advantage in clinical, but, it still be limited in clinical application, for immunological rejection and risk of infection. Artificial prosthetic replacement have a fine early-stage effect and great joint mobility and is also permitted at early stage after the fixation, highly praised by some scholars. But artificial prosthetic replacement is expensive and have some problems in long-term effect. Replantation of inactivated tumor bone is simple in use and without immunological rejection, nevertheless, the process of inactivity may cause destruction of articular cartilage and result in worse postoperative function of joint. Furthemore, replantation of inactivated tumor bone is not suitable for severe cases.The utilization of in situ microwave ablation in treatment of limbs bone tumor can preserve the bone framework at maximum, which can avoid bone ununion. However, it had to be mentioned that microwave ablation still need to face some problems, for example, the high incidence rate of fracture and recurrence. The specific indications of operational reconstruction for tumors around the knee joint and early-stage or long-term mechanical effects of different kinds of reconstruction methods are still not clear.From 2009, we applied in situ microwave ablation combined with internal fixation and prosthetic replacement to treat for distal femur invasive or malignant bone tumor. In this study, we intend to objectively evaluate these two methods In terms of biomechanics, so as to provide guidance for clinical work.[Objective]In this study we applied novel computer simulation softwares(computer-assisted ergonomics and biomechanics software:A nyBody) and a portable joint kinematics measurement system to figure out the following questions from the point of biomechanics.1.With the utilization of finite element, we managed to simulated the optimal boundary conditions and explored biomechanics of human femur during the daily activities.2.On this basis, we managed to figure out the relationship of risk of fracture and lesion range of distal femur tumors in in biomechanical angle.3.To investigate the biomechanic effects of microwave induced hyperthermia on femur and explain the high risk of fracture after microwave ablation.4.With the application of a novel joint kinematics measurement system to establish a reference standard of normal knee kinematics, with the purpose of providing instructions towards postoperative functional rehabilitation..5.Aimed at two clinical reconstruction methods(in situ microwave ablation combined internal fixation and prosthesis replacement), this research is about to assess respective advantages and disadvantages of them in biomechanical angle.[Method]1.A11 volunteers’femoral CT data were extracted and performed in three-dimensional reconstruction and grid operation, using a medical imaging processing software, namely Simpleware. A computer simulating software, Anybody, was used to simulate the normal movements when people walking on the ground and export the muscle force attached to femur in the whole movement process. Then, we use Geomagic studio and Hypermesh to match the coordinate between target model and model provided by Anybody and load the muscle force to femur. After that, we performed finite element analysis in Abaqus, to analyze the size and concentrated areas of von Mises stress and strain on fermur in gait process.2. After successfully interacting Anybody and Abaqus together, we started to focus on how the defect range of distal femur effects the risk of fracture. All volunteers’femoral CT data were performed in three-dimensional reconstruction, and different scales of bone defect, including cancellous bone defect, cortical bone defect (50% scale), cortical bone defect (70% scale), cortical bone defect (85% scale), were simulated in the distal femur. Then, we performed the same steps with method 1 and predict the risk of fracture.3. We divided a fresh femur into forty blocks with same size of 0.5×0.5×1cm3. Those blocks were equally divided into two random groups, microwave group and control group, respectively. Microwave group were ablated in conditions as 100W,30 minutes, and 80℃. Both of two groups were performed static biomechanical testing using, biomechanical testing machine, and the elasticity modulus and yield strength of two groups were calculated. At the same time, another fresh femur was proceeded microwave ablation. Two Micro-CT scan were performed before and after the microwave ablation. With the Micro-CT scan, the BMD (bone mineral density) of femur were calculated two times and the before-and-after comparison was conducted. In the meantime, the radiation scope of microwave was also observed.4. Twenty-eight healthy Chinese subjects (56 knees) were studied during their treadmill gaits. A set of optical marker clusters were attached to the thighs and shanks of each subject, who was tracked by an optical joint kinematics measurement system. Knee landmarks were initially digitized with respect to the marker cluster sets to determine the local coordinate systems for calculation of 6DOF knee joint kinematics. The range of motion (ROM) in 6DOF and 5 kinematic parameters were calculated and compared between bilateral knees and genders.5.11 patients who have received treatment of distal femur tumor microwave ablation or prosthetic replacement between March,2009 and October,2014 were extracted, including 6 cases of microwave ablation and 5 cases of prosthetic replacement. The average postoperative time is 28 months in microwave group, compared to 31.5 months in prosthetic replacement group. Following Method 4, only the affected side was measured in all patients, using a optimum speed chose by patients themselves. The ROM values in 6 DOF of two groups were collected and comparison between groups was performed. Statistical analysis were conducted using double independent sample T test. All data of patients were analyzed and compared to normal people, in aid of evaluating the level of postoperative recovery.[Results]1. The value of von Mises reached the maximum of’27.7 MPa during mid-stance phase of the gait cycles, which was located on inferior and interior lesser trochanter. Stress concentration with the value of 22.6 MPa was observed on the superior lesser trochanter and the femoral neck during the early stance. The value reached the minimum of 0.62 MPa while during the contralateral loading phase. The maximum stress of femur during the swing phase concentrated on mid-diaphysis, and the value was 3.52MPa. It was also mid-stance when the maximum of strain with the value of was 0.39mm observed. The maximum strain of femur during the swing phase concentrated on mid-diaphysis. Strain reached the minimum walue of 0.03 during the swing pahse, which was concentrated on caput femoris.2. The tendencies of von Mises stress during the gait were similar among the 4 models. Stress reached the maximum during mid-stance phase of the gait cycles. While the cortical defects of distal femur were 85%, the stress reached the maximum value of 172MPa, which was clsed to the ultimate stress. Stress concentration was observed on medial malleolus and posterior fossa intercondyloidea. The rest 3 models showed smaller and much the same stress values.3. The yield stress values of control and microwave groups were 105.8±15.7MPa, 101.2±20.7MPa, respectively. And elasticity modulus values of control and microwave groups were 4.5±1.1GPa,4.3±1.4GPa, respectively. No statistical difference was observed between groups. According to the result of Micro-CT scan, decrease of BMD can be observed in the center of ablation. The region was about 4cm of femoral shaft, but no statistical analysis was conducted.4. Two flexion peaks were observed in the tibiofemoral joint:the first flexion peak occurred in the early stance phase (at about 17% of the gait cycle), and another peak at about 73% of the gait cycle. Rotations in axial and coronal planes as well as proximodistal and mediolateral translations showed similar patterns to the flexion-extension pattern of the knee. We observed that when the knee started to flex at heel strike, the femur externally rotated and laterally shifted with a varus angle and a proximal translation. We also noted that in anteroposterior translation, the first peak occurred slightly before toe-off and the second one at about 86% of the gait cycle. These results showed a high degree of consistency in motion patterns compared with previous published data.No statistical difference was found between left and right knees either in the ROMs or in the 5 kinematic parameters. However, the ROM in the mediolateral direction during gait was found to be higher in men than women (P=0.014). In addition, the femurs of female subjects rotated more internally than the femurs of male during the stance phase (P=0.011).5. There was no statistical difference in ROMs in 6 DOF between microwave group and prosthesis replacement group. Subjects’ROMs in axial rotation and flexion-extension showed similar magnitude to that of normal subjects, while ROMs in other freedom showed limited motion.[Conclusion]1. During the mid-stance phase of gait cycle, the value of stress reaches the maximum, which is located on inferior lesser trochanter and mid-diaphyseal segments of the femur.2. While the cortical defects of distal femur were 85%, the medial femoral condyle was in high risk of fracture, particularly during the loading stance of gait cycle.3. Microwave ablation for femoral cortical bone can lead to degradation of biomechanical property, which should be proved based on further studies.4.The novel portable system we introduced can precisely and effectively evaluate knee kinematics.5. Males show different knee kinematic characteristics with female, but no statistical difference can be found between left and right knees.6. In the terms of biomechanics, microwave ablation achieves the same consequence of rehabilitation in the early-to-mid follow-up evaluation. |
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