Biomechanics And Clinical Study On Patellofemoral Joint After Total Knee Arthroplasty

BackgroundTKA has become a very effective way in curing advanced arthritis and other diseases concerning knee joint. Early designs of total knee prostheses did not include a patellar resurfacing component and were reported to be associated with a 40% to 58% rate of anterior knee pain. With the appearance of modern total condyle prostheses, patellar resurfacing tends to be the important part of standard TKA. However, the initial complication rates ranged from 4% to 50% with the reported complications including patellar fracture, disruption of the extensor mechanism, osteonecrosis, aseptic loosening, instability and dislocation, "overstuffing" of the patellofemoral joint, catastrophic failure, patella polyethylene wear, and patellar clunk syndrome. In fact, patella complications arc the main reasons for the revision of TKA. The revision of patellar prosthesis amounts to 50% of revision of TKA. An increasing rate of complications with the extensor mechanism after patellar resurfacing led to the concept of selective resurfacing of the patella in total knee arthroplasty. However, "selectively patellar resurfacing" itself has high uncertainty because of the complexity of patellofemoral joint. The results of several randomized controlled clinical trials have shown that such factors as preoperatoin anterior knee pain, weight, patella cartilage deterioration of "selectively patellar resurfacing" could not properly predicate thc possibility of anterior knee pain after TKA.The lack of definitive prospective data on this subject has led surgeons to following onc of 3 stratcgies: always resurface the patella, never resurface the patella, or selectively resurface the patella depending on the clinical and intraoperative findings. Some randomized prospective study shows that most TKA, whether with patella resurfacing or not, could have the predicted good results. The results have the ame conclusion that whether the patella is resurfaced or not, the anterior knee pain after TKA is related to the design of the implant and proper surgical techniques.The optimal design of femoral component probably includes a deep trochlear groove that extends far enough distally to maintain support of the patella in flexion and avoids catching of the patella on its edges, and a anatomic trochlear groove, and a more anatomic radius of curvature to reproduce optimal patellar tracking.The critical surgical factors in patellar resurfacing are maintaining the preoperative patellar thickness, performing a symmetric bone resection, and balancing the extensor mechanism. This can be achieved by using a caliper before and after patellar resection to ensure that the composite will reproduce the preresection patellar thickness and that equal bone thickness remains in all locations. Underresection can lead to restricted flexion and anterior knee pain. Overresection can predispose to fracture. Asymmetric resection can lead to patellar instability. A patellar cutting guide can assist in achieving more consistent patellar cuts. Trial reduction is necessary to assess tracking. The "rule of no thumb" is often recommended to assess the need for lateral release.Component positioning appears to be critical to optimization of patellar tracking. Different studies have suggested that optimal positioning is medial and superior placement of the patellar component, external rotation and lateral placement of the femoral component, and lateral placement of the tibial component. Component orientations that should specifically be avoided include femoral or tibial internal rotation, anterior placement or flexion of the femoral component, and increasing the anteroposterior diameter of the distal femur by oversizing the femoral component. Several factors are also important when the patella is not resurfaced.Usually, the mechanic experiment will not be used directly on living body. It is considered to be a golden standard to use biological mechanic experiment on cadaver specimen. But because of the limited number and the individual difference of cadaver specimen, so such experiments will influence the accuracy of the results. Using a computer mode, we can, on one hand, reduce cost, save time and eliminate the difference of specimen, and on the other hand accurately simulate the mechanics of living body using controlled experiment conditions. Therefore, we establish a computer model of human knee to simulate TKA so as to analyze the influence of femoral component rotation and patella resurfacing technique on patellofemoral after TKA. Furthermore, randomized prospective study is also done to compare the clinical results of whether patella is resurfaced or not during TKA. Based on this, the study is divided into the following steps:Part one: Development and validation of a three dimensional knee modelObjective The three dimensional anatomical configuration model of the human knee has been developed and validated to compute the kinematics of patellofemoral joint.Methods According to the model building principle from point to line to area to volume of mimics software, a three dimensional anatomical configuration model of the knee joint was reconstructed on the basis of the images of CT and MRI. In addition, quadriceps, ligaments and other soft tissues are defined as non-linear fiber, meanwhile simulating knee extension activity with input variable of quadriceps forcesResults An effective three dimensional anatomical configuration model of the knee joint, including meniscus, articular cartilage and bone, was reconstructed. Some kinematics parameters are calculated based on the model. Compared with the published experimental results, our model is also available.ConclusionsA three-dimension anatomical configuration model of the knee joint, which can reflect the real geometry structures of knee joint and can be used as a basement for subject-specific finite element simulation is reconstructed. It is useful for some kinematic parameters of patellofemoral joint to be computed based on this model.Part two:Effect of femoral component rotation on biomechanics of patellofemoral during total knee arthroplasty Objective To study the biomechanics of the patellofemoral following total knee replacement. More specifically, we investigated the effect of rotational alignment of femoral component of a PFC total knee replacement on the patellar tracking and patellofemoral contact pressures.Methods We used a validated computer simulation of the knee joint to virtually insert the femoral component with the following several types of placements: (1) neutral position, the femoral component that was aligned parallels with the transepicondylar axis, (2) 1 degree and 2 degrees of internal rotation, (3) 1 degree and 2 degrees of external rotation. The patellar 3D tracking and patellofemoral contact pressures were computed for each femoral component placement.Results (1) The internal and external rotation of femoral component relative to surgical epicondylar axis leads to the changes of rotation and tilt of patella. (2) The internal and external rotation of femoral component influence the X axis shift. The external rotation of femoral component increases patellar shift on the X and vice versa. (3) The internal rotation of femoral component causes the significant increase of PFCF in the stage of active flexion and vice versa.Conclusions The position of patellar component mainly affects the patella tracking: the external rotation of femoral component may cause the subluxation of patella; the internal rotation of femoral component may cause the increasing pressure of patellofemoral joint, therefore causing the patellofemoral joint complications.Part three: The influence of patellar resurfacing technique on biomechanics of patellofemoral joint following total knee arthroplastyObjective To study the influence of patellar resurfacing technique on patellofemoral kinematics and contact characteristics during TKA, specifically patellar thickness and asymmetry.Methods We used validated computer simulation of the knee joint to implant a standard PFC total knee replacement prosthesis. Then we changed such parameters as the thickness and thinness, the medial and lateral tilt of patella. In the end, we would have the result of the patellar tracking and compression considering all the possible situations.Results (1) In the whole process of simulation, the thicker the patella, the bigger the tilt of patella, and vice versa. (2) When the knee flexion exceeds 60°, the rotation of patella became bigger with the increasing thickness of patella. (3) The more the thickness of patella, the more patellofemoral contact pressure. (4) The changes of patella thickness had no obvious influence on the shift of patella on X, Y, Z axis (5) When the patella thickness is increasing, PT/QT will increase accordingly and so does the contrary. (6) The rotation and tilt of patella would be greatly influenced by the patellar asymmetry. (7) Lateral tilt of patella influences the shift increase of patella on X axis and vice versa; but has no overt influence on the Y and Z axis. (8) In active flexion stage, the lateral tilt of patella leads to the increase of PFCF; in natural knee flexion, lateral or medial tilt caused the increase of PFCF. (9) In the later stage of natural knee flexion, and active knee flexion, PT/QT would be significantly increased by lateral tilt of patella and vice versa.Conclusions The surgical technique of patellar resurfacing during TKA should attempt to reproduce the original patellar thickness.Part four: Patella resurfacing versus nonresurfacing in total knee arthroplasty, a prospective randomized study with four to five years of follow-up.Objective To investigate differences in the clinical outcome of total knee arthroplasty according to whether or not patellar resurfacing had been performed in prospective, randomized study of 60 osteoarthritic knees.Methods From January 2002 to December 2002, 60 patients (60 knees) undergoing primary total knee arthroplasty for the treatment of osteoarthritis were enrolled in a prospective, randomized study. All patients received the same posterior cruciated substituting total knee prosthetic components. Patients were randomized to treatment with or without resurfacing of the patella, and the results were followed for a mean of fifty-four months (forty-eight to sixty months).Evaluations consisted of the determination of a Knee Society clinical score, range of motion for knees, patient satisfaction, and radiographs.Results With the numbers available for study, we could detect no significant difference between the knees that had had patellar resurfacing and those that did not with regard to the over-all score (p=0.12), the subscore for pain(p=0.90), and patient satisfaction(p=0.22).The results showed the same prevalence of any anterior knee pain in two groups was 10%. This did not represent a significant difference. The two groups showed statistical difference with regard to the total function score and range of motion.Conclusions It has shown that total knee arthroplasty with or without patella resurfacing dramatically relieves pain and improves function. It seems likely that postoperative anterior knee pain is related either to the component design or to the details of the surgical technique, rather than to whether or not the patella is resurfaced. The decision to resurface the patella or not when performing a primary total knee arthroplasty must be individualized on the basis of the surgeon's training, experience and an intraoperative assessment of the patellofemoral articulation. Component design and surgical technique are major factors in successful TKA. According to our study, to avoid the complications related to patellar resuffacing, we might consider not to resurface the patella in osteoarthritis, particularly if a patella-friendly femoral component is used. The most important thing is precise and correct surgical technique in TKA.