| 1. A Cadaveric Study of Relationships among Rotational Alignment Reference Axes of Distal Femur and Tibial Mechanical AxisObjective: Correct rotational alignment of the femoral component is one of the most important factors for successful total knee arthroplasty. Patellar tracking and ligament balance in flexion are affected by the rotational alignment of the femoral component; the imbalance of the flexion gap can also affect the tracking of tibial–femoral joint. The rotational position of the femoral component can be determined using bony landmarks, such as the transepicondylar axis, the posterior condylar axis, or the Whiteside's line. The current study was to investigate the relationships among rotational alignment reference axes of distal femur and tibial mechanical axis, determine the safest rotational alignment reference axis,and discuss its biomechanical advantages.Method: Thirty cadaveric lower extremities obtained from the anatomical department were studied. There were twelve left lower extremities, eighteen right lower extremities. The gender and age of the cadaveric lower extremities were unknown. None of the specimens had gross deformities, no osteoarthritis, the medial and lateral collateral ligaments, the anterior and posterior cruciate ligament, the medial and lateral meniscus were all intact. Skin, muscles, excess soft tissues, patella and the anterior part of the knee capsule were removed from each lower extremity, whereas collateral ligaments and intra-articular structures (the anterior and posterior cruciate ligament, the medial and lateral meniscus) were left intact.Guided by an ACL cannulated drill–aiming jig, 2 pieces of Kirschner wire (2mm in diameter) were drilled through each distal femur. One passed through the lateral epicondylar prominence and the most prominent point of the medial epicondyle, represented the clinical epicondylar axis, the other one passed through the lateral epicondylar prominence and the medial sulcus of the medial epicondyle, represented the surgical epicondylar axis.Digital camera was fixed 80cm anteriorly from lower extremity with the visual axis perpendicular to the tibial axis, and focused to the center of the knee. Digital photos were taken with knee in extension and flexion at 90°, photos include femoral head proximally and medial malleolus distally with knee in extension. When the photos were taken with knee in flexion at 90°, anterior femoral cortex and medial malleolus were included.Digital photos were inputted to the personal computer, the radiographic measurements were performed using Adobe Photoshop CS Image processing software. The femoral mechanical axis was defined as the line connecting the center of the femoral head and the center of the knee, whereas the mechanical axis of the tibia was defined as the line connecting the center of the knee and the center of the talus. Angles were measured among tibial mechanical axis and a line perpendicular to clinical epicondylar axis, a line perpendicular to surgical epicondylar axis, Whiteside's line and femoral mechanical axis, positive value implied the line measured varus relative to the tibial mechanical axis, whereas negative value implied valgus. Statistical analysis was performed using SPSS 11.0, and Wilcoxon signed rank test was used.Results: The angles among the tibial mechanical axis and a line perpendicular to the clinical epicondylar axis, a line perpendicular to the surgical epicondylar axis, Whiteside's line, and femoral mechanical axis were–4.7°~7.0°, 0.3°~11.0°,–10.4°~10.7°,–2.8°~8.3°respectively, the mean and standard deviation were 0.6°±3.0°, 3.9°±2.7°,–0.2°±4.8°, 3.0°±3.0°respectively. The difference of angles among the tibial mechanical axis and the clinical epicondylar axis, the surgical epicondylar axis, and a line perpendicular to Whiteside's line between knee extension and knee flexion was–12.0~4.1°,–7.8°~7.6°,–18.7°~6.8°respectively, the mean and standard deviation were–2.3±3.8°, 0.9±3.6°,–3.1±5.5°respectively. The angle between the femoral mechanical axis and the tibial mechanical axis was significantly larger than the angle among the tibial mechanical axis and a line perpendicular to the clinical epicondylar axis, the Whiteside's line (p<0.05).There was no significant difference compared with the angle between a line perpendicular to the surgical epicondylar axis and the tibial mechanical axis and the angle between the femoral mechanical axis and the tibial mechanical axis (p>0.05).Conclusion: The surgical epicondylar axis rather than the clinical epicondylar axis or the Whiteside's line can maintain a more predictable orientation with respect to the tibial mechanical axis when moving from flexion into extension; however, a certain amount of gap imbalance between flexion and extension can occur because of anatomic variations, a certain amount of ligamentous release still will be necessary.2. Radiographic Study of Tibial Component Rotational Alignment Reference Landmarks of the Proximal TibiaObjective: The rotational relationship between the femoral and tibial components is an important factor affecting the overall function and durability of a total knee arthroplasty. Malalignment of the femoral and/or tibial component has been associated with patellofemoral complications such as tilting, subluxation, dislocation, accelerated wear, loosening, and fracture. The surgical epicondylar axis has been established as the optimal rotational alignment reference for femoral component in the current study. Several reference techniques for establishing tibial rotational alignment have been proposed, such as the posterior condylar line of the tibia plateau, the transcondylar line of the tibia and the midsulcus line of the tibial spine. However, these axes may be difficult to determine intraoperatively given the osteophytes, bone loss, anatomic variation, and deformity seen at the proximal tibia in this patient population. Aligning the tibial component with the medial 1/3 of the tibial tubercle has been stated to maximize function. This may have been established empirically, because there was no theoretical background of this technique. Furthermore, it has been reported that aligning the tibial component with the medial 1/3 of the tibial tubercle will result in excessive external rotation in some cases. The medial border of the patellar tendon attachment was also proposed as a rotational alignment reference for tibial component. This study was to compare the difference between the two anatomical references relative to the surgical epicondylar axis, and evaluate its'reliability for tibial component rotational alignment.Method: Fifteen healthy volunteers were enrolled in this study. Each knee was performed CT scanning. During scanning, the volunteers lied down in a supine position, with both knees in full extension and put together closely, the toes pointed upward. Transverse CT scans of each knee were obtained, ranging from femoral condyle proximally to the tibial tubercle distally. All the CT scan images were inputted to the personal computer, two of the CT scan images of each knee were selected for measurement, the femoral side CT scan image on which the lateral epicondylar prominence and the medial sulcus of the medial epicondyle could be recognized, the tibial side CT scan image is the one that passed through 10 mm distal to the lateral tibial plateau (the cutting surface of the tibia when perform the primary TKA). The selected CT scan images were analyzed and measured using the professional medical image processing software Dicomviewer. The surgical epicondylar axis was defined as a line connecting the most prominent point of the lateral femoral epicondyle and the deepest point of the sulcus of the medial femoral epicondyle. On the femoral side CT scan images, the most prominent point of the lateral femoral epicondyle and the deepest point of the sulcus were determined on the software, a line was drawn connecting the two anatomical landmarks. The angle (γ) between the surgical epicondylar axis and the transverse axis of the image was also measured. On the tibial side CT scan images, a line perpendicular to the surgical epicondylar axis was drawn, the angle between this line and the longitudinal axis of the image equaled to the angle between the surgical epicondylar axis and the transverse axis of the image. Two anteroposterior axis (AP and AP') of the tibia in an extended knee position, a line that connecting the medial border of the patellar tendon and the middle of the posterior cruciate ligament insertion and a line that connecting the medial 1/3 of the patellar tendon and the middle of the posterior cruciate ligament insertion, were drawn on the tibial side CT scan images. Because the patellar tendon could be more clearly identified than the tibial tubercle, we used the medial 1/3 of the patellar tendon to represent the 1/3 of the tibial tubercle in this study. The angles were measured between the two tibial anteroposterior axes and a line perpendicular to the surgical epicondylar axis. All the measuring procedures were performed by three researchers in our study group together in a same time, and all anatomic landmarks and reference axes were determined by three researchers with consensus. The accuracy of measurement value of each angle was 0.1°. Positive value indicated the tibial anteroposterior axis was in an internal rotation position relative to the line perpendicular to the surgical epicondylar axis, whereas the negative value indicated the tibial AP axis was in an external rotation position relative to the line perpendicular to the surgical epicondylar axis. The statistical analysis was performed using student's t test, the software used was SPSS 11.0, and probability values less than 0.05 were considered statistically significant.Results: One right knee of a female volunteer with lateral subluxation of the patella observed on the CT scan, three knees which the most prominent point of the lateral femoral epicondyle and the deepest point of the sulcus of the medial femoral epicondyle could not be clearly identified or could not be identified in a same CT scan image, were excluded from the study. Finally, twenty–six CT scan images of the knees were measured in this study. The mean angle between the line that connecting the medial border of the patellar tendon and the middle of the posterior cruciate ligament insertion and the line perpendicular to the surgical epicondylar axis was 0.7°±2.8°, ranging from ?5.1°to 5.8°, there was no significant difference between the two lines(P>0.05). The mean angle between the line that connecting the medial 1/3 of the patellar tendon and the middle of the posterior cruciate ligament insertion was 6.9°±5.3°, ranging from ?3.4°to 14.1°, there was significant difference between the two lines(P<0.05). The line that connecting the medial border of the patellar tendon and the middle of the posterior cruciate ligament insertion was approximately parallel to the line perpendicular to the surgical epicondylar axis, whereas the line that connecting the medial 1/3 of the patellar tendon and the middle of the posterior cruciate ligament insertion was comparatively external rotational relative to the surgical epicondylar axis, there was significant difference between the two tibial AP axis (P<0.05).Conclusion: The current study compared the relationships between the tibial reference land marks, the medial border of the patellar tendon, he medial 1/3 of the patellar tendon, and the surgical epicondylar axis, the results indicated that the line that connecting the medial border of the patellar tendon and the middle of the posterior cruciate ligament insertion was approximately parallel to the line perpendicular to the surgical epicondylar axis, when aligning the tibial component with the medial border of the patellar tendon, there would be an ideal rotational alignment relationship between the femoral and tibial component, optimizing the patellofemoral joint and femur–tibial joint tracking, maximizing the postoperative knee function. In the current study, although the line that connecting the medial border of the patellar tendon and the middle of the posterior cruciate ligament insertion was in an average 0.7°external rotation relative to the line perpendicular to the surgical epicondylar axis, there were comparatively large angles between the he line that connecting the medial border of the patellar tendon and the middle of the posterior cruciate ligament insertion (the maximal internal rotation was 5.1°, the maximal external rotation was 5.8°). Therefore, when aligning the tibial component with the medial border of the patellar tendon, the surgeon should combine using the self alignment method to appropriately adjust the position of the tibial component.3. Measurement of the posterior condylar offset and the posterior tibial slope of normal knees and the influence of its relationship to the flexional functionObjective: At deep knee flexion postoperatively, the mobility is limited by the impingement occurring between the posterior femoral cortex and the posterior borders of the tibial plateaus. The restoration of the posterior tibial slope has been shown to delay the tibial–femoral impingement. Studies have shown that the maximal knee flexion relative to the posterior condylar offset, which was important factor in delaying the tibial–femoral impingement. The surgical techniques, especially the cutting method, could affect the posterior condylar offset and the posterior tibial slope. Thus, carefully planned bone cuts may increase the range of flexion obtained before impingement occurs and thus substantially improve knee flexion range. Although there are anatomical differences of normal knees in race, gender and individual, each normal knee can reach the ideal flexion angle. The current study was to measure the posterior condylar offset and the posterior tibial slope of the normal knees and analyze the influence of its relationship to the flexional function.Method: A true lateral radiograph of thirty knees of fifteen healthy adult volunteer were obtained for measurement. To derive an accurate and reliable measurement of the posterior tibial slope and the posterior condylar offset, the radiograph should include 1/3 of the distal femur, 2/3 of the proximal tibial with the femoral condyles superimposed. All the lateral radiographs were inputted into the personal computer, analyzing and measurement of the lateral radiograph were performed using professional medical image processing software (Dicom viewer). The posterior condylar offset was defined as the maximal height of the posterior condyle which projected posteriorly to the tangent of the posterior cortex of the femoral shaft. For the difference of magnification among radiographs, there was no comparability among measurements of the absolute value of the posterior condylar offset. For this reason, we measured the relative value of the posterior condylar offset relative to the diameter of the distal femur, without any error from small differences in magnification between the individual radiographs, and compared this relative value of the posterior condylar offset with the posterior tibial slope. Lines were drawn on the lateral radiograph using software Dicomviewer. Line A was drawn tangential to the posterior cortex of the femur, line A intersected with distal posterior cortex of the femur. From this intersection, line B was drawn perpendicular to line A anteriorly reaching the anterior cortex of the femur, representing the diameter of the distal femur. Line C was a vertical line of line A drawn from the most posterior point of the medial posterior condylar, representing the height of the posterior condyle. Quotient Z was determined by dividing the condylar height (C) by the diameter of the distal femur (B). Z describes the relation between the condylar height and the diameter of the distal femur. The larger Z value indicates more posterior prominent of femoral condyle. The posterior tibial slope defined as the angle between the line perpendicular to the proximal tibial anatomical axis and the tangent line of the medial tibial plateau. the proximal tibia anatomical axis D was drawn as a line connecting midpoints of two lines which were drawn randomly connecting the anterior and posterior cortex of the proximal tibia, line D extended proximally passing though the medial tibial plateau. Line E was then drawn parallel to the articular surface of the medial tibial plateau. The angleθwas measured between line D and line E, the posterior tibial slope angleαequals 90°subtractsθ. positive slope values corresponded to a posterior slope, and Negative slope values corresponded to an anterior slope. All the measuring procedures were performed by three researchers in our study group together in a same time, and all anatomic landmarks and reference axes were determined by three researchers with consensus. The precise of measurement value of each angle was 0.1°. Pearson's correlation test was used for correlation evaluations between the posterior condylar offset and the posterior tibial slope. P values less than 0.05 were regarded as statistically significant.Results: All the knees included in this study could accomplish squatting; the heel could reach the buttocks when kneeling on the ground. There were no varus or valgus deformities in the knee joints observed on radiographs. There were no signs of ostarthritis, such as narrowing of joint space, subchondral bone sclerosis, subchondral cyst, osteophytes formation. There were no signs of bone tumor. Skeletal growths were all completed. Five radiographs did not correspond to the measuring criterion were exclude from the study because of the both condyle were not superimposed. The mean posterior slope of the medial tibia plateau with reference to the proximal tibia anatomical axis was 12.03°. The degree of posterior tibial slope varied widely among the subjects, ranging from 5.11°to 20.54°. The mean relative height of the medial posterior condylar was 0.95, ranging from 0.695 to 1.236. There was no correlation found between the posterior tibial slope and the relative height of the medial posterior condylar (R2=0.017).Conclusion: There was no correlation found between the posterior tibial slope and the relative height of the medial posterior condylar in the current study, the degree of posterior tibial slope and the relative height of the medial posterior condyle also varied widely among the subjects. In spite of these findings, postoperative TKA knee kinematic studies have shown that the posterior tibial slope and the posterior condylar offset play an important role in delaying the tibial-femoral impingement to maximizing the knee flexion function, therefore, when performing the posterior condylar cut, pay attention not only the rotational alignment of femoral component, but also to maintain the posterior condylar offset equals to the diameter of the distal femur(the point that posterior femoral cortex tangential to the curve proximal to the posterior condyle ) after the posterior condylar cut has been accomplished and the femoral component has been fixed. In spite of our results that the mean posterior slope of the medial tibia plateaus was 12.03°with reference to the proximal tibia anatomical axis, because over posterior slope can induce more stress to the posterior part of tibial insert, increase the tenseness of the extensor mechanism, and also the limitation of sampling error of our study, considering other's studies described in the literature, we propose that the posterior tibial slope be maintained in 10°. Kinematic mode of normal knee between the femur and tibia is affected by multi of factors when moving from extension to flexion. Besides the configuration of distal femur and proximal tibia can affect the Kinematic mode of normal knee, other factors, as well as the mechanism that the movement between the femur and tibia guided by the variation of cruciate ligament tension during knee moving from extension to flexion, the mode of menisci movement to accommodate the movement between the femur and tibia, should be further studied.
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