Experimental And Clinical Study On Rotational Alignment Of Tibial Components In Total Knee Arthroplasty And Its Biomechanical Influence On Tibial-femoral Joint

Part One Analysis of the relationship between tibial anteroposterior axis and other anatomies of ChineseObjective: To investigate the relationship between tibial anteroposterior axis and other anatomies in determining the rotation of tibial prothesis in total knee arthroplasty using computed tomography. Methods: Transverse CT scans of 40 volunteers' right knee with the knees in full extension were made. The anteroposterior axis of the tibia was defined as a line perpendicular to the transepicondylar axis and passing through the middle of the posterior cruciate ligament. At the tibial plateau and optimum resection level, the mean medial percentage width of intersection point of the patellar tendon and the anteroposterior axis was measured. The mean angle between the anteroposterior axis and a line connecting the middle of the posterior cruciate ligament and the medial of the patellar tendon and the medial 1/3 of the patellar tendon were measured. Results: At the tibial plateau level, the mean medial percentage width of intersection point of the patellar tendon was 10.1%±8.3%. At the optimum resection level, the mean medial percentage width of intersection point of the patellar tendon was 0.2%±10%. At the optimum resection level, the mean angle between the anteroposterior axis and a line connecting the middle of the posterior cruciate ligament and the medial of the patellar tendon was 0.1°±2.7°.The mean angle between the anteroposterior axis and a line connecting the middle of the posterior cruciate ligament and the medial 1/3 of the patellar tendon was 10.3°±3.6°. Conclusion: There was a tendency to align the tibial component in external rotation relative to the femoral component when the medial 1/3 of the patellar tendon was used. The line connecting the middle of the posterior cruciate ligament and the medial of the patellar tendon can be used as a reliable axis for correct rotational orientation of the tibial component.Part Two Comparison of two techniques determining the rotation of tibial component at TKAObjective: To compare two most commonly used techniques determining the rotational alignment of tibial component during total knee arthroplasty. Methods: 30 patients who had unilateral TKA were enrolled. On proximal tibial cut surface, the rotational orientation of the tibial trial determined by the ROM technique was marked on the anterior tibial cortex as well as the medial 1/3 of the patella tendon. The angles between the anteroposterior axis of tibia and lines connecting the middle of the posterior cruciate ligament and these two points were measured. Results: On proximal tibial cut surface, the mean angle between the anteroposterior axis and a line connecting the middle of the posterior cruciate ligament and the medial 1/3 of the patella tendon was 11.3°±3.4°.The mean angle between the anteroposterior axis and a line connecting the middle of the posterior cruciate ligament and the ROM mark was 0.8°±2.2°Conclusion: There is a tendency to align the tibial component in external rotation relative to the femoral component when the medial 1/3 of the patellar tendon is used. When the femoral component is set paralleling to the transepicondylar axis and correct soft tissue release has been done, the ROM technique can be used as a more reliable technique for correct rotational orientation of the tibial component.Part Three Determination of Neutral Tibial Rotational Alignment in Rotating Platform TKAObjective: To compare the neutral rotational position determined by the rotating platform TKA with the most medial aspect and 1/3 of the tibial tubercle during total knee arthroplasty. Methods: 30 patients who had unilateral TKA were enrolled. All the knees used rotating platform TKA. After trial components were inserted with the knee properly balanced, we recorded the neutral point of the rotating tibial insert, in extension, relative to the most medial aspect of the tibial tubercle. Divergence of the neutral point was recorded as being internal or external to the medial border of the tibial tubercle to the nearest 5°increment. Results: The neutral rotational position determined by the rotating platform TKA had a mean divergence of 2.3°±3.4°external to the medial border of the tubercle, which was typically smaller than the angle between the AP axis and the line connecting the middle of the PCL and 1/3 of the of the tibial patellar on CT. Conclusion: The neutral rotational position of the tibial prostheses is close to the medial aspect of the tibial tubercle. There is a tendency to align the tibial component in external rotation relative to the femoral component when the medial 1/3 of the tibial tubercle is used.Part Four Experimental Study on Rotational Alignment of Tibial Components in Total Knee ArthroplastyObjective: To investigate the effect of tibial rotational malalignment on tibiofemoral contact pressures and contact areas of fixed bearing TKA. Methods: We tested 5 fresh-frozen cadaveric knees using a custom knee jig which permited the simulation of static loading conditions. An electronic resistive pressure measuring sensor was used to detect the contact stress and areas between the tibilfemoral joints at deferent angles. The tibial rotation was first determined by the anteroposterior axis of the tibia and then was internally and externally rotated from 5°to 10°and 15°.Results: When the knee was at fully extension, both the lateral and medial tibiofemoral contact pressure was smallest and the contact area was largest when the tibial rotation was determined by the AP axis. The malrotation caused the decrease of the contact area and the improvement of the contact pressure. During the knee's flexion, the smallest contact pressures were not always obtained at the tibial neutral rotational position. When compared at the same flexion and tibial rotational angles, we found the internal rotation had larger influence on the medial tibiofemoral contact pressure than the lateral, and the external rotation had larger influence on the lateral tibiofemoral contact pressure the medial. Conclusion: To fixed bearing TKA, the malrotation of tibial prosthesis will increase the contact pressure and decrease the contact area between tibiofemoral joint when the knee was at fully extension. But during the flexion of the knee, the neutral rotational position of the tibial prostheses was not always the best, which suggests us that there is not the real neutral rotational position to the fixed bearing TKA.