The Measurement Of The Femur Posterior Condylar Angle With Digital Three-dimensional Reconstruction Technique

BackgroundRecently, more and more people accept the total knee arthroplasty (TKA) totreat Osteoarthritis in China. However, the incidence rate of postoperative patellofemoral complications is higher in our country than developed country. The reason is the knee anatomical characteristics of Chinese is not deeply discussed and analysised. Femoral component malrotation is a major reason of patellofemoral complications. The definition of surgical epicondylar axis and the measure of Posterior Condylar Angle(PCA) are used for establishing femoral rotational alignment during total knee arthroplasty. They have already turned to be the focus and most popular reseach topics in anatomy and the total knee arthroplasty. Patellofemoral complications such as subluxation, dislocation. patellar clunk, eccentric wear and anterior knee pain resulted from poor patellar tracking have been reported. Patellofemoral complications are the most common postoperative problem associated with the current design of total knee prostheses and one of the major reasons for revision surgery. Precision measurement of Posterior Condylar Angle (PCA) can supply reasonable referenced parameters of the rotational alignment for the total knee arthroplasty. It may Improve durability of the knee prosthesis. The measurement of PCA includes traditional anatomy measurement on femurs of adult cadavers and the image measurement. Traditional anatomy research focus on sectioning, observation and measurement. The disadvantage of traditional anatomy have artifical influence factors that can lead to errors. Furthermore, cadavers cadaver specimens are expensive. As the development of imaging technique, The image of MR and CT provide some information of three dimensions, but we get the bidimensional image infact. Bidimensional image cover up informations of human body because it is three-dimensional structure. The measure of PCA is not accurate on bidimensional images of MR and CT because of its three-dimensional angle.As the development of digitizing three-dimensional reconstruction technique of computer, it is possible to change the bidimensional medical image into three-diamensions dynamic image. Three-diamensions image can supply more information for the three-dimensional structure of biological tissue. More important, Three-diamensions image can be observed in any angle and direction. Therefore, Digitization technique may supply a new method for the precision measurement of PCA. Our object is base on the research of other scholar. We utilize the CT image of normal adults knees to reconstrue three-dimension image.We want to precisely measure PCA based on the reconstructed distal Femur visible models by Mimics 10.0.ObjectiveTo introduce a new method of precision measurement of PCA based on three dimentional reconstruction of CT images of the normal distal femurs by measurement tool of Mimics10.0. The data of PCA may provide reasonable referenced parameters of the rotational alignment for the total knee arthroplasty. Furthermore, we investigate the feasibility of this method for the individual design of the femoral component for the total knee arthroplasty.Methods1. Subjects and collection of images(1) Between June in 2007 and October in 2007, CT scanning of the thirty-two normal knees in adults: 64knees, 18 males 36 knees, and 14 females 28 knees (without disease and injury in knees before), The knees was conducted(2) Device: GE Medical systems/light speed(3) CT scanning of the knees of 64 normal adults.The ambit is 10cm in centrage of the joint space . Scanning condition: 120 kV, 300 mAs, Scanning parameters: the width of collimating device is 0.75 mm; thickness is 0.75 mm; slice thickness is 0.625 mm; the pitch is 0.75mm. The time of scanning one slice is 200 ms; the total time of scanning is 10-12s. The datas of scanning images conserve in PC by DICOM.2. Three dimensions reconstruction of the distal femurs.We input the CT image of the knee in the software of Mimics 10.0 and obtain the three-dimendion model of the normal distal femurs.3. Analyze image of the three-dimendion model of the normal distal femurs and measure PCA.We can observe image of the three-dimendion model of the normal distal femurs in any angle and direction by tool of Mimics 10.0. The bony landmarks of PCA for determining the posterior condylar angle was made on the three -dimensional images of the the normal distal femur. We can precisely mark four bony landmarks by measure tool of Mimics 10.0. Point 1 is the lateral epicondylar prominence; Point 2 is the medial sulcus. The line between Point 1 and Point 2 is the surgical epicondylar axis; Point 3 and Point 4 are the femoral posterior condylar surfaces.The line between Point 1 and Point 2 are the posterior condylar line. The PCA are the angle of the surgical epicondylar axis and the posterior condylar line. We find and mark Point 1,Point 2,Point 3 and Point 4 on the three-dimendion model of the normal distal femurs by meaure and analyze tool of simulation modular in Mimics 10.0. Then we could get the degree of PCA directly.4. Statistics AnalysisThe experimental data was analyzed by the software of SPSS 13.0, Independent-samples t test and pair-sample t test were used, and an associated probability of 5% (P≤0.05) was considered significant.ResultsWe could obtain satisfactory morphous and darity boundary in the three-dimendion model of the normal knee. By the tool of region growing, we can removal the images of tibia and fibula and only display the image of distal femurs. The bony landmarks for determining the posterior condylar angle is marked and the degree of PCA can be easily got by the measurement tool of Mmics 10.0 directly.1. The effect of the three-dimendion model of the normal distal femurs. The model of the normal distal femurs image have good stereoacuity. We could observe them in any angle and direction and get the anatomical character. The bony landmarks of PCA can be marked precisely and immediately.2. The data of PCA.(1) In the 36 knees of male, The PCA is 4.39°±0.69°; In the 28 knees of female, the PCA is 4.57°±0.58°. There is no statistical significant difference in gender (t=-1.068; P =0.290) . (2) The PCA were 4.33°±0.67°in left side, 4.45°±0.72°in right side. There is no statistical significant difference in sides (t=-1.039; P =0.307) .(3) All data is Gaussian distribution (P=0.685) . The mean degree of PCA is 4.46°±0.54°.Conclusion1. It is feasible to make the three-dimensional reconstruction of the normal knee joint on the basis of the CT sectional images.We could obtain satisfactory morphous and darity boundary in the three-dimendion model of the normal knee joint and the three-dimendion model of the normal distal femurs without distortion. The model of the normal distal femurs image have good stereoacuity. We can observe it from any angle and direction, remove dodge part and show the part we want to see by the lucidification.2. It is feasible to measure PCA on the three-dimensional reconstruction model of the normal distal femurs by Mimics 10.0.We could marked the bony landmarks for determining the PCA and get the degree of PCA which can be easily directly by the tool of measurement in Mimics 10.0. This method of measurement limits artifical influence factor that can lead to errors. so it provides a new idea for the measure research of the anatomy.3. The data comparison between measure by the three-dimensional reconstruction and other mothod.The result is that the mean degree of PCA is 4.46°±0.54°in our study. This data is diffient from Westerns.The reason is either the anatomy of Chinese is diffient from Westerns or advancement of measure technique.4. The method can be useful in clinic and provides a new idea for personalized method of measurement. It can provide reasonable referenced parameters of the rotational alignment for the personalized total knee arthroplasty.The personalized total knee arthroplasty is development direction of total knee arthroplasty. The personalized measurement of PCA and osteotomy is key to the personalized total knee arthroplasty. We not only investigate a new digitizing and personalized method of measurement for the PCA on the three dimentional reconstruction of CT images, but also offer an ideal preoperative prepare for the personalized total knee arthroplasty. First, the patient is scaned by CT in preoperative. Second, We input the CT image of the knee to the software of Mimics 10.0 and obtain the three-dimendion model of the normal distal femurs. Third, We analyze image of the three-dimendion model of the normal distal femurs and measure PCA. This method can supply reasonable referenced parameters of the rotational alignment for the total knee arthroplasty in abstracto.