Morphological Measurement And Application Of Distal Femur And Proximal Tibia Of Digital Chinese Knees

BackgroundIncreasing number of Chinese patients with osteoarthritis accept the total knee arthroplasty (TKA).Total knee replacement is a precision surgery. It requires accurate bone cutting, adequate balancing of the soft tissues and proper coverage of the resected bony surface by the components for achieving a successful outcome. It has now become a routine orthopedic procedure for the Asian-Pacific population.Asian subpopulations are known to have a smaller build and stature compared with their Western counterparts. This leads to the problem of an implant size mismatch with the resected bony surface in the Asian patients. Most prosthesis used in China come from Western countries, the size and shape of which are mainly for foreigner and not for Chinese. It's known that Asian ofen grow shorter and smaller than Westerner. It is necessary for us to take the measurement of Chinese knees in order to design and select the right size of knee prosthesis.It is known that the tibial component is more prone to complications in total knee arthroplasty (TKA) as compared to the femoral component. It becomes important to properly size the prosthesis to the cut surface of the distal femur and proximal tibia to achieve the best stability and longevity for the implant. There is a paucity of anthropometric data on the distal femur and proximal tibia in the Asian population. A component that matches the anthropometry of the Chinese population may be expected to give better results.The measurement methods include traditional anatomical measurement and image measurement. Traditional measurement focus on measurement through surgery or by anatomy. But it may be hard to get specimens for us. Experts have been carrying out researches on knee measurement and protheies design by X-ray. As X-ray images showing two-dimensional construction only, scientists start to take their studies with technology of CT and MRI. But neither of them could show 3D construction. Few study about section of the distal femur and proximal tibia is reported, which seems to ignore the fact that prosthesis is just fixed to the section of bone.Three-dimensional reconstruction can be got by section images with its orginal freqency. As two-dimenional images translated into three-dimensional, much message about the object could be received. And the three-dimensional object can be observed in any direction. In a sum, digital technique may supply a new method for precisitive measurement of knee. Based on research of other scholars, we utilize CT images of normal Chinese knee to reconstruct three-dimensional images. The knee digital model can be cut and measured by the software Mimics10.0. With the study we explore the possibility of three-dimensional reconstruction and measurement technique for TKA application.We evaluated the anthropometric data on the distal femur and proximal tibia that was obtained from a large number of Chinese cadavers by using computer tomography, and we compared these measurements with the dimensions of the commonly available TKA prostheses in Chinese. Furthermore, the pattern of change of the mediolateral dimensions in relation to the anteroposterior dimensions was compared between the study population and the currently available prosthesis. Based on these results, a distal femur and tibial prosthetic component that follows the same pattern seen in the study population is suggested.Objective1. To create a new method to measure the bone-cutting section of knee. 2. To identify the difference of distal femur and proximal tibia between male and female in order to provide experimental base for prosthesis design for male/female.3. To identify the difference of bone section among different cutting height and provide the experimental basis for the right height of distal femur and tibial bone cutting for TKA.4. To compare Chinese bone section with other nation and provide accurate and full-scale applied anatomical basis for the Chinese knee prosthesis design.Methods1. Subjects and collection of images1.1 The study was performed on 112 normal knees obtained from 52 male and 60 female cadavers that were without any gross congenital anomaly or deformity. The average age at the time of death was 41.3 years (23-61 years) for the males and 46.5 years (25-56 years) for the females. The average height was 172.6 cm for the males and 159.1 cm for the females, and the average tibial length was 32.1 cm (30.2-36.6 cm) for the males and 30.3 cm (26.4-33.8 cm) for the females. All the measured data was verified by two of the authors independently and statistical analysis was performed using the Student t-test and the Paired t-test.1.2 Device:GE Medical systems/light speed1.3 The fresh cadavers were placed supine in the scanner with both knees taped to the scanner platform in the extended position with the patella facing towards the ceiling. The bony measurements were obtained by performing 1 mm computer tomography (CT) slices from the hip joint to the ankle joint of the cadaver. Scanning condition:120kV,300mAs. Scanning parameters:the width of collimating device was 0.75mm; thickness was 0.75mm; slice thickness was 0.625mm; the pitch was 0.75mm. The time of scanning one slice was 200ms; the total time of scanning was 10-12s. The data of scanning images was conserved into PC by DICOM. 2. Three dimensional reconstruction of kneeA three dimensional (3D) image of the knee joint was reconstructed on the computer using the program Mimics, whereas the bony cuts and measurements were done using the program Pro/ENGINEER Release.3. Measurement of distal femur and proximal sectionsThe index of measurement included Parameters of mediolateral (ML), medial and lateral anteroposteriordimensions (MAP/LAP) of the section of proximal tibia0 The osteophytes surrounding the distal femur and proximal tibial cut surface, if any, were excluded from the measurements. The proximal slice (cut) was performed perpendicular to the mechanical axis of the tibia,6 mm below the lateral tibial plateau with 7°of posterior inclination. We compared theML and AP values with the height of the person to assess for any correlation between them. The medial anteroposterior (MAP) dimension was taken as the length of line drawn parallel to the middle anteroposterior line (AP) and passing through the posterior-most point of the medial tibial condyle. The lateral anteroposterior (LAP) dimension was taken as the length of line drawn parallel to the middle anteroposterior line (AP) and passing through the posterior-most point of the lateral tibial condyle. The distance of the MAP and LAP from the central point C was measured as CM and CL, respectively. We compared our measurement values with the previous published data. Itwas utilized to predict the shape of the prostheses based on theMLandAP dimensions.4. Measurement of prosthesisThe measurement values thus obtained were compared with those similar values from two commonly used prosthetic designs:PFC (DePuy-Johnson and Johnson, Warsaw, IN) and Nexgen (Zimmer, Warsaw, IN). All these products were found to be mediolaterally symmetrical. The variation in aspect ratio with increase in the anteroposterior dimension for the study population was analyzed, and compared to that of the commercially available symmetric prosthesis. A design was generated for the component for the study population that has an aspect ratio that varies with size based on the data collected.5. Statistics AnalysisStatistical analysis was performed by using the Student t-test, the Paired t-test and Pearson's correlation coefficient using SPSS for windows (version13.0, SPSS, Chicago, IL). Values for pb0.05 were regarded as significant. Pearson's correlation coefficient was represented as r.Results1,The three-dimentional model of knee with satisfactory morphous and darity boundary was obtained. By the tool of "region growing" of Mimics, the distal femur and proximal tibia could be shown in isolation. The bony landmarks determining the dimenion parameters of the distal femur and proximal tibia were drawed and the measurement result were got by Pro/ENGINEER Release。The widths of medial and lateral femoral condyles were similar with those of medial and lateral tibial platforms. The width of femoral condyle was 1.01～1.08 times of that of tibial platform wherea it was 1.12～1.23 times of sagittal length of femoral condyle. There was positive correlation between the width of femoral condyle and the width of tibial platform. The medial and lateral posterior condyles had similar radii and radian. The transepicondylar axis (TEA) could be looked as the fixed flexion axis of the knee approximately.2. All data including ML, MAP and LAP of the section of proximal tibia was Gaussian distribution. Parameters of ML of the proximal tibia section were obtained.The mean was 70.91±5.28mm, ranging from 64.30 to 79.31mm in section 1. The mean was 71.40±5.30mm, ranging from 64.60 to 79.75mm in section 2. The mean was 71.89±5.33mm, ranging from 64.90 to 80.51mm in section 3. Statistical significant difference existed between section 1 and section 3 (P<0.05).It was found that the implants with smaller AP dimensions were undersized in the mediolateral dimension whereas those implants with larger AP dimensions showed mediolateral overhang; this was more evident in the male population. Among the two conventional symmetric knee prostheses, the Duracon design followed the morphologic data most consistently compared to the others, irrespective of the gender and this was statistically significant as shown by the Student t-test(pb0.05).3. To anticipate the shape of the prostheses that is suitable for the Chinese population, we calculated the aspect ratio and compared it with the AP dimension of the proximal tibia. The aspect ratio of the proximal tibia depicted a progressive decline with the increasing AP dimension, irrespective of the gender. On comparison with the prostheses, we found that the Duracon prostheses followed a similar pattern of fall in the aspect ratio while the others showed either no change in the aspect ratio or an increase in the aspect ratio with the increasing AP dimension of the tibia, irrespective of the gender. Though the aspect ratio in the Duracon design decreased with increase in the anteroposterior dimension, the rate of change of the aspect ratio was less than that of the study population. Significant different existed in sections between sex and among diferrent bone cutting height. Sex and resection levels should be taken into account when we design tibia prosthesis and or choose the imported prosthesis in the total knee arthroplasty.4. There was statistical significant difference between the data of male and female (P <0.05)Conclusions1. The normal parameter database of the healthy Chinese knee is found. It is facility for the related analysis and research of the morphology of the knee by using computer-aided design. It is feasible to make three-dimensional reconstruction of knee on the basis of CT images. The model is with satisfactory morphous and darity boundary without distortion. It also have a good stereoacuity and could be observed from any angle or direction. We could remove the dodge part and show the part we need by lucidification. 2. The digital model could be cut and measured. With the help of 3D model, we could get accurate data of the lined-parameter of knee, which is the base of prosthese design and could reduce the complications of TKA such as prosthesis loosening. Our study provides anthropometric data of the resected proximal tibia in the Chinese population.3. Significant different existed in sections between sex and among diferrent bone cutting height. Sex and resection levels should be taken into account when we design tibia prosthesis and or choose the imported prosthesis in the total knee arthroplasty. The geometry and anatomy of knee in Chinese people have significant differences from the Western people. Care should be taken when we use the prosthesis designed by Western people. We suggest redesigning the aspect ratio of the tibial component to match the shape of the proximal tibia in the Chinese population. Based on these results, a tibial prosthetic component that follows the same pattern seen in the study population is suggested.This study may serve as a guideline for the development of tibial prostheses suitable to a majority of the Chinese. This study may serve as a guideline for the development of tibial prostheses suitable to a majority of the Asian subpopulations.