| Background Bone tumor is a kind of tumor that occurs in bone or originates from various components of bone tissue. Bone tumor was divided into benign, intermediate and malignance by WHO in 1993. The morbidity of bone tumor is 0.01%. The malignant bone tumors account for 1% of human malignant tumors approximately and often occur in teenagers. Before 1970 s, amputation is the main treatment of malignant bone tumors. However, the recurrence rate is high. With the development of surgical resection and reconstruction and the progress of radiotherapy and chemotherapy, limb salvage operation has become the main trend. It has been reported that 85%-95% patients can be treated with limb salvage treatment. Artificial joint replacement associate with radiotherapy and chemotherapy improves the quality of life of the patients. The significantly improvement of the survival rate of malignant bone tumor and the success rate of limb salvage as well as the extension of the survival time of the patients, express more requirements on the function and long-term stability of long transection joint replacement. Bone tumors are more likely to occur around the knee joint. Tumor knee replacement is able to reconstruct the knee function, and the patient could regain the ability of walking in a short time. A large number of clinical studies show that the survival time was significant different. Until now, the length and the volume of the prostheses are the only two considerations in prostheses design. Other parameters such as coronal tibiofemoral angle, tibial plateau-diaphysis angle, posterior slope angle of tibial plateau and the compatibility between intramedullary needle and medullary canal, has not been stressed. However, these parameters have significant effect on the long-term function, the stability and the wear of the prostheses. Aseptic loosening is related to the biomechanical, mechanical and patientrelated factors. From the post-operation follow-up of the patient who accepted knee replacement but suffered loosening, the misalignment of the force line between the prosthesis and bone in sagittal plane might be the main reason of loosening. In this study, the force line in sagittal plane was measurement, and the match relation between bone and prosthesis in sagittal plane was validated by FEA. This study provide theoretical basis for the prosthetic installation and design. The curative effect of 25 giant cell tumor knee prosthesis replacements was validated in this study.Objective The morphological characteristics of the femur was obtained from the analysis of 86 tumor knee replacements in this group. The reason of short-term loosening was validated according to the alignment of the force line between femur and prosthesis. Theoretical basis for the prosthetic installation and design was provided in this study. The clinical curative effect of 25 cases of artificial knee replacement in giant cell tumor of bone around knee was analysis retrospectively.Methods A retrospective analysis of our hospital in January 2000-2014 in January of clinical data for total knee replacement prosthesis 86 cases of bone cancer patients, imaging data, measuring preoperative lateral femoral bone marrow diameter and diameter bone wall thickness; femoral prosthesis based on bad line sagittal assumptions, the mathematical model for finite element analysis; measuring postoperative 86 cases a year, three years, five years, X-ray, statistics sagittal femoral angle difference with fake physical line loosening effect on the proposed prosthesis improved method; on line 25 patients with tumor segment tumors excised human cytomegalovirus limbs + labor joint prosthesis reconstruction. Every three months later after chest and limb lateral X-ray, using assessment criteria Enneking limb prosthesis joint function and survival. All results were statistically analyzed using SPSS16.0, P <0.05 was considered statistically significant.Results 1.Femoral morphology measurement:In the anteroposterior X-ray, the diameter of male femur and the medullary cavity are all greater than the female’s. There is a statistical significance between male’s and female’s. In the lateral X-ray, there was no statistical significance. From the point of view of morphology, cortical bone from the posterior-lateral are elliptically thicker than the anteromedial in the middle of the femur, the bone marrow cavity is not a circle. In sagittal position, The radian of distal femur is smaller than the middle of the femur, the femur sagittal degree varried from each age level, and increased with aging process. 37 cases were randomly selected from 86 patients, The femur sagittal radian of different age stages respectively: under the age of 12, 6.5—8.5 cm apart from the small rotor, radian is 6—8°; 12 to 20 years old, apart from the small rotor 9—11 cm,,radian is 7—9°;more than 20 years old, apart from small rotor 11—13 cm, radian is 8—10°.2. Finite element model of retrieved prosthesis was built and misalignment of 3°and 6° between the axis of intramedullary needle and the mechanical axis of femur in eight direction was given to the model. The displacement of medullary cavity wall is more than 0.58 mm(0.58 mm is the maximum displacement of cancellous bone could suffer). The misalignment between the axis of intramedullary needle and the mechanical axis of femur has significant influence on the displacement of medullary cavity, the displacement at 6°is twice as much as that of 3°。The self-adaption of bone results in uneven stress at bone and prosthesis. The physiological line of force was changed because of the uneven stress, and further lead to stress shielding and aseptic loosening.3. 86 cases of patients, 2 cases have a more than 3° offset angle of force line between the femur and prosthesis in coronary X-ray taked 1 month after operation, accounted for 2.3% only. 2—5 years after operation, the offset angle in 4 cases is greater than 3 °, accounted for 4.7%, the maximum offset angle is 3.68 °. 2 cases appeared more than 2 mm bright area around the prosthesis, identified may be loose. 9 cases have a more than 3° offset angle of force line between the femur and prosthesis in sagittal position X-ray taked 1 month after operation, accounted for 10.4%. 2—5 years after operation, the offset angle in 13 cases is greater than 3° in sagittal position X-ray, accounted for 15.1%, the maximum offset angle is 14 °, and 5 cases appeared more than 2 mm bright area around the prosthesis. There are 8 cases with prosthesis shifted, or broken. 5 cases for prosthesis sinking or loosening received revision surgery.4.25 cases were followed up for 20 to 168 months. According to the Enneking bone tumors objective standard, we evaluat the postoperative function of limb, excellent in 20 cases, good in 2 cases, medium in 3 cases, and no poor case. Excellent and good rate was 88%. 5 cases have prosthetic aseptic loosening or fracture in total 25 cases, in whom all suffering a femur bone giant cell tumor and undergoing artificial joint replacement, and the loosening occurred all in the side of femur. The use of time are 2 years, 7 years, 10 years, 14 years, respectively; One case received revision surgery for prosthesis sinking or loosening 2 years after operation. 2 cases received revision surgery 10 years later. One case have a limited of joint activities after 4 years,Through exploratory operation, we find out that is caused by scar tissue contracture of back prosthesis. It is recover through the line of release joint capsule as normal.Conclusion The shape of middle femur is elliptical. Posterolateral cortical bone is thicker than anteromedial cortical bone. Medullary canal is not regular circle shape. The radian at 1/3 proximal femur is obvious. The maximum displacement at medullary cavity wall is larger than the allowable displacement when the misalignment between the axis of intramedullary needle and the mechanical axis of femur is more than 3°. Stress shielding and aseptic loosening will occur. The main reason of loosening is the misalignment between femur and prosthesis in sagittal plane. From this point, intramedullary needle with certain radian that match the physiological form of medullary canal will be the best choice. The effect of the new design on tumor segment resection and artificial joint replacement is satisfactory. However, the longterm complications are still frequent. The further research would pay attention to the reduction of the complication and the recurrence rate. |
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