Post-cam Design Research Articles

Effect of post-cam design on the kinematics and contact stress of posterior-stabilized total knee arthroplasty.

The post-cam mechanism in the posterior-stabilized (PS) implant plays an important role, such as durability and kinematic performances, in total knee arthroplasty (TKA). The purpose of this study was to evaluate the difference in the kinematics and contact stress of five post-cam designs, which are flat-and-flat, curve-and-curve (concave), curve-and-curve (concave and convex), helical, and asymmetrical post-cam designs, using three-dimensional finite element models. We designed the post-cam model with five different geometries. The kinematics, contact stress, and contact area were evaluated in the five post-cam designs under gait cycle loading conditions using the finite element method. There were no differences in the contact stress and area on the tibial insert in all designs. The largest internal rotation was shown in the swing phase for the helical design, and the largest tibial posterior translation was observed for the curve-and-curve (concave) design. The curve-and-curve (concave) design showed the lowest contact stress and the largest posterior tibial translation during the gait cycle. Considering the kinematics and contact stress, we found that the curve-and-curve (concave) design was more stable than other designs. From the results, we found the important factors of TKA implant considering stability and kinematics.

Effect of geometric variations on tibiofemoral surface and post-cam design of normal knee kinematics restoration

BackgroundRestoration of natural knee kinematics for a designed mechanism in knee implants is required to achieve full knee function in total knee arthroplasty (TKA). In different posterior-stabilized TKAs, there are wide variations in tibiofemoral surfaces and post-cam design. However, it is not known whether these design variations preserve natural knee kinematics. The purpose of this study was to determine the most appropriate tibiofemoral surface and post-cam designs to restore natural knee kinematics of the TKA.MethodsA subject-specific finite element knee modal was used to evaluate tibiofemoral surface and post-cam design. Three different posts in convex, straight, and concave geometries were considered with a fixed circular cam design in this study. In addition, this post-cam design was applied to three different surface conformities for conforming, medial pivot, and subject anatomy mimetic tibiofemoral surfaces. We evaluated the femoral rollback, internal-external rotation, and quadriceps muscle force under a deep-knee-bend condition.ResultsThe three different tibiofemoral conformities showed that the convex post provided the most natural-knee-like femoral rollback. This was also observed in internal rotation. In surface conformity, subject anatomy mimetic tibiofemoral surfaces showed the most natural -knee-like kinematics and quadriceps force.ConclusionsThis study confirmed that convex post design and subject anatomy mimetic tibiofemoral surfaces provided the most natural-knee-like kinematics. This study suggested that post-cam design and tibiofemoral surface conformity should be considered in conventional and customized TKA.

Intraoperative kinematic analysis of posterior stabilized total knee arthroplasty with asymmetric helical post-cam design

To investigate intraoperative kinematics during passive flexion using a surgical navigation system for knees undergoing posterior stabilized (PS) total knee arthroplasty (TKA) with an asymmetric helical post-cam design using navigation system. In total, 45 knees with both pre- and postoperative kinematic data available were included in the study. Intraoperative kinematic measurements were performed during the course of surgery using the software incorporated in the navigation system. Measurements were performed at the following two time points: (1) before TKA procedure and (2) after TKA implantation. Among the kinematic parameters studied, anterior/posterior translation and axial rotation during flexion were subjected to the analysis. Before surgery, physiologic anterior/posterior translational pattern of the tibia during flexion (rollback of the femur) was found in only 15.6% of the knees. After TKA implantation, postoperative kinematic measurement showed no significant change in the tibial translational during knee flexion. Similarly, with regard to rotation, non-physiologic external tibial rotation in early flexion was observed in the majority of the knees before surgery, and this abnormal kinematic pattern remained after the TKA procedure. The intraoperative three-dimensional motion analysis using a navigation system showed that the physiologic kinematic pattern (anterior translation and internal rotation of the tibia during flexion) of the knee was distorted in osteoarthritic knees undergoing TKA. The abnormal kinematic pattern before surgery was not fully corrected even after implantation of the PS TKA designed to induce natural knee motion; however, no clear relationship between the intraoperative kinematic pattern and knee flexion angle at one year was demonstrated, and the effect of knee kinematics on postoperative knee function and patient's satisfaction is still unclear.

Effect of Post-Cam Design for Normal Knee Joint Kinematic, Ligament, and Quadriceps Force in Patient-Specific Posterior-Stabilized Total Knee Arthroplasty by Using Finite Element Analysis.

The purpose of this study is to investigate post-cam design via finite element analysis to evaluate the most normal-like knee mechanics. We developed five different three-dimensional computational models of customized posterior-stabilized (PS) total knee arthroplasty (TKA) involving identical surfaces with the exception of the post-cam geometry. They include flat-and-flat, curve-and-curve (concave), curve-and-curve (concave and convex), helical, and asymmetrical post-cam designs. We compared the kinematics, collateral ligament force, and quadriceps force in the customized PS-TKA with five different post-cam designs and conventional PS-TKA to those of a normal knee under deep-knee-bend conditions. The results indicated that femoral rollback in curve-and-curve (concave) post-cam design exhibited the most normal-like knee kinematics, although the internal rotation was the closest to that of a normal knee in the helical post-cam design. The curve-and-curve (concave) post-cam design showed a femoral rollback of 4.4 mm less than the normal knee, and the helical post-cam design showed an internal rotation of 5.6° less than the normal knee. Lateral collateral ligament and quadriceps forces in curve-and-curve (concave) post-cam design, and medial collateral ligament forces in helical post-cam design were the closest to that of a normal knee. The curve-and-curve (concave) post-cam design showed 20% greater lateral collateral ligament force than normal knee, and helical post-cam design showed medial collateral ligament force 14% greater than normal knee. The results revealed the variation in each design that provided the most normal-like biomechanical effect. The present biomechanical data are expected to provide useful information to improve post-cam design to restore normal-like knee mechanics in customized PS-TKA.

Tibiofemoral conformity variation offers changed kinematics and wear performance of customized posterior-stabilized total knee arthroplasty

Posterior-stabilized (PS)-total knee arthroplasty (TKA) can be applied in any of several variations in terms of the tibiofemoral conformity and post-cam mechanism. However, previous studies have not evaluated the effect of the condylar surface radii (tibiofemoral conformity) on wear in a customized PS-TKA. The present study involved evaluating the wear performance with respect to three different conformities of the tibiofemoral articular surface in a customized PS-TKA by means of a computational simulation. An adaptive computational simulation method was developed that conduct wear simulation for tibial insert to predict kinematics, weight loss due to wear, and wear contours to results. Wear predictions using computational simulation were performed for 5million gait cycles with force-controlled inputs. Customized PS-TKA designs were developed and categorized as conventional conformity (CPS-TKA), medial pivot conformity (MPS-TKA), and anatomical conformity (APS-TKA). The post-cam design in the customized PS-TKA is identical. We compared the kinematics, contact mechanics, and wear performance. The findings revealed that APS-TKA exhibited the highest internal tibial rotation relative to other TKA designs. Additionally, the higher contact area led to there being less contact stress although it did not directly affect the wear performance. Specifically, MPS-TKA exhibited the lowest volumetric wear. The results of the present study showed that tibiofemoral articular surface conformity should be considered carefully in customized PS-TKA design. Different wear performances were observed with respect to different tibiofemoral conformities. Even though APS-TKA exhibited an inferior wear performance compared to MPS-TKA, it proved to be better in terms of kinematics so its functionality may be improved through the optimization of the tibiofemoral articular surface conformity. Additionally, it should be carefully designed since any changes may affect the post-cam mechanism.

Post-Cam Design and Contact Stress on Tibial Posts in Posterior-Stabilized Total Knee Prostheses: Comparison Between a Rounded and a Squared Design

BackgroundThe post-cam mechanism in posterior stabilized (PS) prostheses plays an important role in total knee arthroplasty (TKA). The purpose of this study is to clarify the difference of the contact stress on the tibial post between a rounded post-cam design and a squared design during deep knee flexion and at hyperextension using the three-dimensional (3D) finite element models. MethodsWe created 2 types of 3D, finite element models of PS prostheses (types A and B), whose surfaces were identical except for the post-cam geometries: type A has a rounded post-cam design, while type B has a squared design. Both types have a similar curved-shape intercondylar notch of the femoral component. Stress distributions, peak contact stresses, and contact areas on the tibial posts at 90°, 120°, and 150° flexion with/without 10° tibial internal rotation and at 10° hyperextension were compared between the 2 models. ResultsType B demonstrated more concentrated stress distribution compared to type A. The peak contact stresses were similar in both groups during neutral flexion; however, the stresses were much higher in type B during flexion with 10° rotation and at hyperextension. The higher peak contact stresses corresponded to the smaller contact areas in the tibial post. ConclusionA rounded post-cam design demonstrated less stress concentration during flexion with rotation and at hyperextension compared with a squared design. The results would be useful for development of implant designs and prediction of the contact stress on the tibial post in PS total knee arthroplasty.

Total Knee Post-Cam Design Variations and Their Effects on Kinematics and Wear Patterns.

Post-cam designs for posterior-stabilized total knee arthroplasy (TKA) implants have evolved over the last 2 decades. These designs have evolved from symmetric post and cam to asymmetric designs that include anterior post interactions to affect a kinematic change in full extension. All design changes have consequences on the resulting femorotibial contact kinematics and, depending on the amount of constraint built into the design, these changes may have significant consequences on the wear patterns on the tibial polyethylene insert. The current authors review the kinematic effects of symmetric and asymmetric cam designs and use a retrieval database of TKA implants obtained at the time of necropsy to show how different design variables may affect polyethylene wear patterns after 10 or more years of implantation or from modeled wear in simulators. More modern designs seem to have moved the post posteriorly and sloped the anterior aspect to avoid impingement of the anterior post in terminal flexion on the inferior aspect of the patella button. [Orthopedics. 2016; 39(3):S45-S49.].

Computational Model for Mechanics of Total Knee Replacement: Effect of Tibial Rotation during Deep Flexion in Relation to Post-Cam Design

Computational Model for Mechanics of Total Knee Replacement: Effect of Tibial Rotation during Deep Flexion in Relation to Post-Cam Design

Effect of Bearing Mobility on the Kinetics Performance of TKA during Deep Flexion: A Computational Simulation

Characterizing the relative performance between mobile bearing and fixed bearing knee prosthesis remains seen as a difficult task as the previous short-term and mid-term clinical studies disable to observe any evidence of superiority of one design over another. The aim of the present study is to characterize the mechanics comparison between both designs of prosthesis during deep flexional motion with tibial rotation. Three dimensional (3D) FE model of clinically used mobile bearing posterior stabilized (PS) prosthesis was developed from its CAD data. Explicit finite element model was used to simulate the dynamic loaded deep flexional motion from 0 to 135° with neutral and 10° tibial rotation. Fixed bearing prosthesis was represented by fixing the tibial insert to the tibial component. The fixed bearing design was found relatively sensitive to flexion motion and tibial rotation in terms of contact area and maximum shear stress as compared to the mobile bearing design. Tibial rotation increased the peak value of maximum shear stress up to 58 MPa for the fixed bearing, on the contrary, the mobile bearing maintained the peak value of maximum shear stress at 31 MPa even with tibial axial rotation. The influence of post-cam design was also discussed in this study. The mobile bearing has an ability to maintain conformity and relatively low shear stress during very deep flexion with tibial axial rotation in comparison to the fixed bearing.

In vivo kinematics of high-flex mobile-bearing total knee arthroplasty, with a new post-cam design, in deep knee bending motion

The objective of this study was to evaluate the in vivo knee kinematics to assess the available functional motion of the characteristic mobile-bearing prosthesis design and to examine whether the artificial joint would work in vivo according to its design concept. We studied 14 knees (11 patients) implanted with the Vanguard RP Hi-Flex prosthesis. This prosthesis has a highly original form of post-cam called a PS saddle design with high compatibility, and with a rotating plate mobile-bearing mechanism. The cylinder-type post-cam is designed to enable contact in early flexion ranges, and to prevent paradoxical anterior femoral component movement. Each patient performed weight-bearing deep knee bending under fluoroscopic surveillance. Motion between each component including the polyethylene insert was analyzed using the 2D/3D registration technique. The mean range of motion was 122.0°. The mean femoral component rotation for the tibial tray was 5.0°. No paradoxical anterior movement of the nearest point was confirmed between the femoral component and the tibial tray in the early flexion ranges. Initial contact of the post-cam was confirmed at a knee flexion angle of 33.8°. Subsequently, the wide contact of the post-cam was maintained until flexion reached 120° in all knees, but disengagement of the post-cam was observed in two knees when flexion was ≥130°. The results of this study demonstrated that the prosthesis design generally works in vivo as intended by its design concept. The present kinematic data may provide useful information for improvement of high-flex type prostheses.

Influence of post-cam design of posterior stabilized knee prosthesis on tibiofemoral motion during high knee flexion

BackgroundsThe post-cam design of contemporary posterior stabilized knee prosthesis can be categorized into flat-on-flat or curve-on-curve contact surfaces. The curve-on-curve design has been demonstrated its advantage of reducing stress concentration when the knee sustained an anteroposterior force with tibial rotation. How the post-cam design affects knee kinematics is still unknown, particularly, to compare the difference between the two design features. Analyzing knee kinematics of posterior stabilized knee prosthesis with various post-cam designs should provide certain instructions to the modification of prosthesis design. MethodsA dynamic knee model was utilized to investigate tibiofemoral motion of various post-cam designs during high knee flexion. Two posterior stabilized knee models were constructed with flat-on-flat and curve-on-curve contact surfaces of post-cam. Dynamic data of axial tibial rotation and femoral translation were measured from full-extension to 135°. FindingsInternal tibial rotation increased with knee flexion in both designs. Before post-cam engagement, the magnitude of internal tibial rotation was close in the two designs. However, tibial rotation angle decreased beyond femoral cam engaged with tibial post. The rate of reduction of tibial rotation was relatively lower in the curve-on-curve design. From post-cam engagement to extreme flexion, the curve-on-curve design had greater internal tibial rotation. InterpretationMotion constraint was generated by medial impingement of femoral cam on tibial post. It would interfere with the axial motion of the femur relative to the tibia, resulting in decrease of internal tibial rotation. Elimination of rotational constraint should be necessary for achieving better tibial rotation during high knee flexion.

Analysis of Weight-Bearing Kinematics of Posterior-Stabilized Total Knee Arthroplasty With Novel Helical Post-Cam Design

We developed a new posterior-stabilized total knee arthroplasty (TKA) with a unique post-cam design that induces and accommodates internal tibial rotation with deep knee flexion. To validate the design concept of this system, we conducted an image analysis study employing a computer-aided diagnosis system for 24 TKA-implanted knees. In the analysis, the tibiofemoral relationship in the following 3 postures was evaluated: standing at extension, forward lunge, and kneeling with maximum knee flexion. The results of the image analysis showed achievement of consistent internal rotation of the tibia in deep flexion with a broad contact area at the post-cam interface as intended by the original design concept of this TKA system.

Contact Stress Analysis of the Conforming Post-Cam Mechanism in Posterior-Stabilized Total Knee Arthroplasty

The present study evaluated the effects of extent of conformity of post-cam design on contact area and stress at post-cam mechanism using 4 different posterior-stabilized prostheses. TRAC and Alpina with full-conformed post-cams exhibited the largest contact area at 90° and 120°. PFC sigma RPF with partial conformed post-cam had the largest contact area at 150°. Scorpio NRG with less conformed post-cam had smaller contact area than the others. Lifting of femoral component decreased contact area and increased contact stress of TRAC and Alpina. Recent modifications of post-cam design have increased contact area, contributing to lower contact stress. None of these prostheses exhibited constant low contact stress throughout flexion. Further modifications of post-cam mechanism are necessary to provide lower contact stress throughout deep knee flexion.

Stress analysis of the anterior tibial post in posterior stabilized knee prostheses

Recent retrieval studies have indicated a high incidence of polyethylene wear on the anterior tibial post caused by impingement. This study investigated the influences of post-cam design features and component alignment on the stress distribution in the anterior tibial post when subjected to the impingement loading. Two three-dimensional finite element models of posterior stabilized knee prostheses were constructed, one with flat on flat (FF) and another with curve on curve (CC) contact surfaces between anterior tibial post and femoral cam. The polyethylene insert was modeled with elastoplastic properties. Nine cases, three hyperextension angles (0 degrees , 5 degrees , and 10 degrees ) combined with three axial tibial rotations (0 degrees , 2.5 degrees , and 5 degrees ) simulating different component alignments were analyzed. A vertical compressive load of 2,000 N and an extension moment of 45 Nm were applied simultaneously. The FF model had larger stress increases than the CC model in both hyperextension and tibial rotation compared with the neutral position. The maximum increase for the FF model was 68% in peak contact stress, 125% in von Mises stress, and 58% in tensile stress in the extreme case of 10 degrees of hyperextension combined with 5 degrees of axial rotation. Stress concentration was found at the anterior corner of the post in the FF model; this was not found in the CC model. The curve on curve design can reduce edge loading on the tibial post, especially during axial tibiofemoral rotation.

Influence of Post-cam Design on Stresses on Posterior-stabilized Tibial Posts

Polyethylene wear and fracture at the tibial post of posterior- stabilized knee prostheses are common complications. Analyzing the stresses on various designs of tibial posts should predict the risk of damage. The post-cam of knee prostheses generally are designed either as flat-on-flat or curve-on- curve contact surfaces. We investigated stress on such tibial posts using a finite element method. We applied a 500-N anteroposterior shear force to the knee at neutral contact and 10 degrees tibial internal rotation when the knee was flexed at 60 degrees , 90 degrees , 120 degrees , and 150 degrees . There was more stress during tibial rotation compared with during neutral contact. The greatest increments of maximum von Mises stress and contact stress in the flat-on-flat model were from 20.4 to 46.1 MPa (126.3%) and from 22.2 to 55.7 MPa (151%), respectively, whereas in the curve-on-curve design they were from 20.5 to 22.7 MPa (10.7%) and from 33.0 to 35.4 MPa (7.2%), respectively. Increased stress concentration at the tibial post occurred at increased flexion angles along with axial tibial rotation. The curve-on-curve design reduced stress concentration when the knee sustained an anteroposterior shear force with tibial rotation.

Contact stress at the post-cam mechanism in posterior-stabilised total knee arthroplasty

We measured the contact areas and contact stresses at the post-cam mechanism of a posterior-stabilised total knee arthroplasty when a posterior force of 500 N was applied to the Kirschner Performance, Scorpio Superflex, NexGen LPS Flex Fixed, and NexGen LPS Flex Mobile knee systems. Measurements were made at 90 degrees, 120 degrees, and 150 degrees of flexion both in neutral rotation and 10 degrees of internal rotation of the tibial component. Peak contact stresses at 90 degrees, 120 degrees, and 150 degrees were 24.0, 33.9, and 28.8 MPa, respectively, for the Kirschner; 26.0, 32.4, and 22.1 MPa, respectively, for the Scorpio; and 34.1, 31.5, and 32.5 MPa, respectively, for the NexGen LPS Flex Fixed. With an internally rotated tibia, the contact stress increased significantly with all the fixed-bearing arthroplasties but not with the NexGen LPS Flex Mobile arthroplasty. The post-cam design should be modified in order to provide a larger contact area whilst avoiding any impingement and edge loading.