The Gender Difference And Relationship Between Femoral Posterior Condylar Offset And Tibial Slope In Normal Knees

BackgroundFemoral posterior condylar offset(PCO)means the maximum thickness of the posterior condyle projecting posteriorly to the tangent of the posterior cortex of the femoral shaft.In order to maximize range of motion(ROM)and avoid impingement,the concept of femoral PCO restoration during total knee arthroplasty(TKA)was first introduced by Bellemans.The sagittal posterior tibial slope(PTS)is the inclination of the tibial plateaus in the sagittal plane.In healthy individuals,the anterior portion of tibial plateaus is usually higher than the posterior one,and the resulting sagittal inclination of tibial plateau is postero-caudally directed.Some authors suggested that,after TKA,the PCO and the PTS may affect the ROM during flexion in different ways.An appropriate sagittal inclination of the tibial component may enhance the flexion space of the joint and prevent the knee from becoming too tight in flexion.A proper restoration of postoperative PCO may increase the space between the posterior femoral cortex and the posterior border of the tibial plateau during knee flexion,thus reducing the risk of impingement between the two.In spite of several investigations have evaluated the influence of PCO and PTS on knee flexion,few of them has analysed,in normal knees,whether there is any deference of the two between medial and lateral compartment,or whether any relationship between them in meidial or lateral compartment.The answer of these two questions are crucial for knee prosthesis designing and intraoperative osteotomy.PurposeThe present study was designed to evaluate,on Multi-slice spiral CT scan,the variability of the PCO and PTS on the medial and lateral compartment of healthy volunteers in South China,and assessing the difference and correlation of the two that may exist in the normal knees.Materials and Methods1.Population selectionThis study comprised a non-randomized,healthy group of 80 volunteers(40 males and 40 females).The inclusion criteria were as follows:people from Guangdong and Guangxi province of China(whose last five generations lived in the two provinces),without knee disorders.According to the patients’ medical history,clinical exam and X-rays,pregnant women and people with the following signs and symptoms of the knee were excluded:pain,deformity,abnormal movement,claudication,rheumatic fever,rickets,rheumatoid arthritis,osteoarthritis,fracture or previous surgery.The average age was 31.38(20-45)years,the average height was 167.25(151-185)cm,and the average weight was 59.99(40-80)kg.Approval from the ethical committee and informed consents were obtained for the protocol.One hundred and sixty scanned knees were available for analysis.2.CT evaluationAll patients were scanned following an identical 64-slice multi slice spiral CT protocol(General Electric,USA).The patients’ legs were fully extended and the feet stabilized in a neutral position.The CT scans were taken with a contiguous thickness of 0.625 mm,from the femoral condyle to the heel,with settings of 120kV and 80mA.Images from each CT scan were saved as DICOM images and recorded on a separate CD-ROM.3.MeasurementThe DICOM images were imported into Mimics Research 20.0 software(MATERIALISE,Belgium)to perform the measurement.For the purpose of this study a sagittal plane perpendicular to the transepicondylar axis(TEA),as visualized on an axial plane through the most prominent center of the femoral epicondyles,was defined as the true-sagittal plane(tsP).To reduce the deviation,we shift this plane to both medial and lateral compartment of the knee to take the measurement.3.1 Sagittal PTSThe medial and lateral PTS was measured separately as the angle created by a tangential line of the tibial plateau and sagittal axis.The tangential line of the medial or lateral tibial plateau was defined as the line passing through the center and both the anterior and posterior edge of it.The sagittal axis in our study were defined as the straight line connecting two midpoints of outer cortical diameter at 5 and 15 cm respectively distal to the knee joint.3.2 Sagittal PCOFirst,the sagittal longitudinal axis of the femur was marked on the central sagittal CT scan and then transferred to the posterior femoral cortex.Second,the center of the lateral and medial condyles was identified on an axial scan.Third,the tangent along the dorsal cortex was transferred to the center of the lateral and medial condyle in the sagittal plane.In this sagittal section,the shortest distance of each tangent along the posterior cortex(medial and lateral)to the most posterior extent of each condyle was measured as the medial and lateral PCO.Statistical analysisMean,95%confidence intervals(CI)and standard deviation(SD)were computed for all measurement sets.The Lilliefors(Kolmogorov-Smirnov)normality test was performed for all assessed variables.Student’s t-test was performed to compare PCO and PTS in both medial and lateral side,and to present differences between the two knees.Paired t-tests were performed for differences between medial and lateral sides.Linear regression analysis was used to determine the relationships between PCO and PTS in both side.The variation coefficient was used to assess the variability of the two.The level of significance was set at 0.05 for all t-tests and the correlation analysis.SPSS for Windows(version 20.0,SPSS,Chicago,IL,USA)was used for the statistical analysis.ResultsBoth PCO and PTS showed a normal distribution on the medial and lateral compartment.The mean PCO was 29.2mm on the medial,and 23.8mm on the lateral side(P<0.001).The mean PTS was 6.78 and 6.11° on the medial and lateral sides,respectively(P=0.002).Which mean the medial PCO and PTS are both greater than lateral ones,and this trend was observed regardless of gender.There is no difference found between left and right knee in the same individual.In medial compartment,PCO of men is larger than women(P<0.001),on the contrary,PTS of men is more flat than women(P=0.016).Which show a significant gender difference of PCO and PTS in medial compartment of normal knees.In medial compartment,a significant negative correlation was found between PCO and PTS(P=0.026).That is,the large the PCO,the flat the PTS.No significant correlation was found on the lateral compartment.ConclusionsIn summary,PCO and PTS are two anatomic parameters that have been shown to have profound influence on knee motion and stability,and both of them can be assessed preoperatively and modified during surgery.The conventional osteotomy eliminate the morphological differences of PCO and PTS in two compartments of the knee.And it may be needed to explore further to answer the question if the gender-specific prosthesis should be designed,and if the reconstruction of the morphological feature of normal knee should be performed to improve the surgical outcome.We assume that the results from our study could provide valuable information as a great emphasis on gender difference and negative correlation between PCO and PTS found in medial compartment.Perhaps because of these difference and correlation,current TKA designs still generate non-physiologic,paradoxical motions,and the reproduction of normal,physiologic knee kinematics has been elusive.If the ultimate design goal of TKA is achievement of normal knee kinematics,it is conceivable that reproduction of the normal surface geometry will help.