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Loading on Attune® fixed-bearing cruciate-substituting total knee implant in knee malalignment during activities of daily living: A finite element analysis
∗Corresponding author: Gautam Shetty. gautams10@gmail.com
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
To compare contact stresses between Attune® and PFC Sigma® total knee arthroplasty (TKA) implants in the presence of knee malalignment.
Maximum contact stress after finite element analysis were compared during standing, walking, and stair climbing in 0°, 2.5° and 5°varus/valgus knee alignments.
The percentage increase in contact stress was highest during walking with PFC Sigma® in 5° varus (238.5%), standing with Attune® in 5° valgus (127.2%), and standing with Attune® in 2.5° valgus (107.8%).
The newer Attune® design may be associated with higher maximum contact stresses and increased risk of wear and implant failure.
Keywords
Contact pressure
Finite-element analysis
Attune total knee replacement
Malalignment
Activities of daily living
1 Introduction
Total knee arthroplasty (TKA) surgeries have proven to be an effective treatment method to relive pain and restore function in patients with severe tricompartmental knee arthritis.1,2 Optimum distribution of load across the knee joint, wear resistance and long term survival of the implant is dependent to a large extent on the biomechanical properties and design of the knee implant.3–5 The presence of malalignment of the limb mechanical axis and implant may adversely affect the function and survivability of TKA by adversely affecting tibiofemoral contact forces and kinematics, increasing the risk of wear and osteolysis, and causing implant failure.6,7 However, an implant design with larger contact area and lower mean and peak contact stresses between the femoral component and tibial insert and increased durability of the insert may decrease the risk of implant failure even in the presence of limb and component malalignment.6
Apart from improvement in surgical technique, knee implants have seen progressive changes in design over the years with the aim to improve postoperative performance and overall long term survivability of the implants.8 Recent TKA implants, such as the Attune ® TKA implant (DePuy Synthes, Warsaw, IN), were introduced to offer greater biomechanical advantage and functional benefits with improvement in implant design and material when compared to older designs such as the PFC Sigma® TKA implant (DePuy Synthes, Warsaw, IN). The Attune® TKA implant had several new design features which included a distal trochlear groove with reduced intercondylar box ratio, a gradually changing multiradii femoral condyle, smaller femoral component profile, S-shaped cam post articulation, central polyethylene locking mechanism, and an antioxidant incorporated ultra-high molecular polyethylene (UHMWPE) insert.9–11
Although recent studies have reported good short-term clinical outcomes with the Attune® TKA implant,12–15 some investigators have reported an increased incidence of radiolucencies and loosing with the Attune® TKA implant.14–18 Furthermore, biomechanical performance of the Attune® TKA implant in terms of contact stress between the femoral component and tibial insert, especially in the presence of knee malalignment, during activities of daily living such as standing, walking, and stair climbing is unclear. Hence, the purpose of this study was to simulate and analyse, using finite element analysis (FEA), maximum contact stress patterns on the Attune® fixed-bearing, cruciate substituting TKA implant in the presence and absence of limb mechanical axis malalignment during simulated activities of daily living such as standing, walking and stair climbing and compare these findings with the traditional PFC Sigma® fixed-bearing, cruciate substituting TKR implant.
2 Materials and methods
2.1 Implant details
For this FE analysis, 2 fixed-bearing, cruciate-substituting, primary TKA prostheses were used. The newer Attune® (DePuy Synthes, Warsaw, IN) TKA implant with a cobalt-chromium (CoCr) alloy femoral and tibial component, and an UHMWPE insert with a proprietary COVERNOXTM® anti-oxidant material and the older PFC Sigma® (DePuy Synthes, Warsaw, IN) TKA implant with a cobalt-chromium (CoCr) alloy femoral component, a titanium alloy (Ti6Al4V) tibial component, and an UHMWPE insert. The material properties of the finite element model were set based on values given in the literature.19–21 The material properties, in terms of Young's modulus and Poisson's ratio, were set as 220,000 MPa and 0.30 MPa for Co–Cr femoral and tibial components, 110,000 MPa and 0.34 MPa for Ti tibial component, and 2000 MPa and 0.44 MPa for UHMWPE insert.19–21
2.2 Prostheses shape acquisition
Prostheses shape was acquired using a 3D laser scanner (Creaform Exascan, Creaform USA Inc, CA, USA) and its VXelements 3D software (ver 6.1, Creaform Inc., Canada). The 3D scanner had an accuracy of <40 μm, measuring volume range of 80 to 1000 mm3, and acquisition time of about 1s. A 3D computer-aided design (CAD) model of both implants was created using the Geomagic Studio software (3D Systems, Inc. Canada) (Fig. 1).
2.3 Intact knee model
A 3D knee model was developed based on the geometry of an intact knee using computed tomography (CT) images of a 35-year-old healthy male subject. The CT image was performed with 1-mm slice thickness using the Siemens Somatom, 16-slice, spiral CT scanner (Siemens AG, Erlangen, Germany). The DICOM format of CT scan images were imported into the 3D Slicer software (3D Slicer, Cambridge, MA) for generating 3D bone model of the lower extremity. Femur and tibia were considered as link elements, and the hip, knee and ankle joints were considered as cylindrical joints.
2.4 Loads and constraints on knee prosthesis
The femoral bone was simulated as a cylindrical bar fixed to the upper component of the knee prosthesis. To determine loads acting on the knee joint during daily activities such as standing, walking and stair climbing, the knee flexion angle (ϕ) was set at 0° for standing, was set at 15° while walking, and at 60° while stair climbing.19 While standing with both feet on the ground, the vertical force due to the body weight (FB) was equally split between the two legs. However, while walking and stair climbing, the whole body weight was transmitted to the ground by means of only one leg. Normal knee alignment (angle between the femoral axis and tibial axis) was set as 0° neutral, 2.5° varus, or 2.5° valgus. The knee alignment was considered malaligned if it was outside the ±2.5° range from neutral knee alignment (0°). Hence, for this study, 5° varus or valgus and 10° varus or valgus were considered malaligned knees for both knee implants. The primary force producing contact pressure between the femoral component and the polyethylene insert of the knee implant was the body force acting axially along the femoral axis (FA).
2.5 FE analysis
The 3D models of the 2 total knee prostheses and knee model were imported into the Ansys Workbench R16.2 software (ANSYS, Inc. USA). To reproduce the behaviour of collateral ligaments and to minimise rotation of femur around its axis, two springs were applied, connecting the tibial to the femoral component and the spring stiffness was set at 34 N/mm as reported for human knee collateral ligament stiffness.22,23 External boundary conditions were applied to the tibia and the femur, the tibial component was fixed in all directions while the femoral component was constrained in the mediolateral and rotational axes. The insert was bonded to the tibial component, and the same bonding was applied between the femoral and tibial bone and the femoral and tibial components. Bonding was modelled as a perfect constrain between the bodies in a way that no mutual movements or rotations were permitted. Friction contact was assumed between the PE insert and the femoral component, with a friction coefficient set at 0.01.19,24 For all the analysed configurations, a reference load of 500 N (FA), which takes into account both the FA force and the axial component of the muscles reaction forces, was applied along the femur axis.19,25
The maximum contact stress on the tibial insert during simulated standing, walking, and stair climbing with the limb mechanical axis in normal alignment (0° neutral, 2.5° varus, and 2.5° valgus) and in malalignment (5° varus or valgus and 10° varus or valgus) were investigated in both the total knee implants. The maximum contact stress for varus alignment was measured on the medial side and for valgus alignment was measured on the lateral side.
3 Results
Overall, the general trends of finite element results of the current study were compared and validated with the findings from previously published FE studies on primary, fixed bearing, cruciate substituting TKA implants in the literature.19,21,28
3.1 Comparison of maximum contact stresses between the 2 implants during standing, walking, and stair climbing in a well aligned knee
In standing, the maximum contact pressure in the femur implant-polyethylene interface was higher in PFC Sigma® implant in 0° neutral, and higher in the Attune® implant in 2.5° varus and valgus (Fig. 2). In walking, the maximum contact pressure was higher in Attune® implant in 0° neutral and 2.5° varus, and higher in the PFC Sigma® implant in 2.5° valgus (Fig. 2). In stair climbing, the maximum contact pressure was higher in PFC Sigma® implant in 0° neutral, and higher in the Attune® implant in 2.5° varus and valgus (Fig. 2).
3.2 Comparison of maximum contact stresses between the 2 implants during standing, walking, and stair climbing in a malaligned knee
In standing, the maximum contact pressure at the femur implant-polyethylene interface was higher in Attune® implant in 5° varus and valgus (Fig. 3). In walking, the maximum contact pressure was higher in Attune® implant in 5° varus and valgus (Fig. 3). In stair climbing, the maximum contact pressure was higher in PFC Sigma® implant in 5° varus, and higher in the Attune® implant in 5° valgus (Fig. 3).
3.3 Percentage change in maximum contact stresses in the 2 implants during standing, walking, and stair climbing with change in knee alignment
During standing, the Attune® knee implant showed maximum percentage increase in contact stress in 5° valgus (127.2%), 2.5° valgus (107.8%), and 2.5° varus (98.4%) when compared to the 0° neutral alignment (Fig. 4). In contrast, the PFC Sigma® knee implant showed maximum percentage decrease in contact stress in 2.5° valgus (55.3%), and 5° varus (35.3%) when compared to the 0° neutral alignment during standing (Fig. 4).
During walking, the Attune® knee implant showed maximum percentage decrease in contact stress in 2.5° valgus (53.9%), 2.5° varus (43.2%), and 5° valgus (24.3%) when compared to the 0° neutral alignment (Fig. 4). In contrast, the PFC Sigma® knee implant showed maximum percentage increase in contact stress in 5° varus (238.5%), and 2.5° valgus (102.6%) when compared to the 0° neutral alignment during walking (Fig. 4).
During stair climbing, the Attune® knee implant showed maximum percentage increase in contact stress in 2.5° varus (84.6%), 5° valgus (59.4%), and 2.5° valgus (22.9%) when compared to the 0° neutral alignment (Fig. 4). In contrast, the PFC Sigma® knee implant showed maximum percentage decrease in contact stress in 2.5° varus (71.5%), 2.5° valgus (68.3%), and 5° valgus (58.6%) when compared to the 0° neutral alignment during stair climbing (Fig. 4).
4 Discussion
The results of our study indicates that in a well aligned knee (±2.5° within 0° neutral alignment), the maximum contact stress was higher in the Attune® knee implant during standing, walking and stair climbing when compared to the PFC Sigma® knee implant. However, in a malaligned knee (5° varus or valgus alignment), the maximum contact stress was higher in Attune® knee during standing and walking, and higher in the PFC Sigma® knee during stair climbing. The maximum percentage increase in contact stress values when compared to 0° neutral alignment was observed during walking with the PFC Sigma® knee implant in 5° varus, during standing with the Attune® knee implant in 5° valgus, and during standing with the Attune® knee implant in 2.5° valgus. Overall, the maximum contact stresses were higher in the Attune® knee implant whereas both varus and valgus alignments (2.5° and 5°) were similar in terms of maximum contact stresses and percentage increase in maximum contact pressure.
Ingrassia et al.,19 in a similar comparison between two posterior stabilised, primary fixed-bearing TKA implant designs using FE analysis, reported that the Stryker® TKA (Stryker Corp. USA) prosthesis was subjected to lower peak stresses when compared to the Tornier® TKA prosthesis (Tornier Surgical Implants, Tornier SAS, France). A difference in the shape of the articulating surfaces (femoral condyle and insert), and the shape and design of the posterior cam of the PE insert between the 2 implants were attributed to more favourable peak stress patterns seen in the Stryker® TKA design.19 In the current study, similar design differences were present between the Attune® and PFC Sigma® knee implants which may have resulted in the difference in maximum stress patterns. The Attune® implant had a more distal intercondylar groove and reduced intercondylar box ratio, an S shaped, concave posterior articulating surface of the post when compared to a more vertical and convex articulating surface of the post in the PFC Sigma® implant, and a continuously varying radii design of the femoral condyle in the Attune® implant when compared to the dual radii design in the PFC Sigma® implant.9–11
Watanabe et al.26 in an FE analysis to study the effect of post-cam design reported that a rounded post-cam design with a concave posterior articulating surface demonstrated less stress concentration during flexion with rotation compared to a vertical post-cam design with a more convex posterior articulating surface. Furthermore, geometric variations of the post-cam design have been reported to affect femoral rollback and tibial internal rotation with anatomy mimetic articular surface, circle cam, and convex post design showing a more natural-knee-like biomechanics.27 Clary et al.28 in an FE analysis to study the effect of TKA implant geometry on mid-flexion stability, reported that differences in femoral condylar radii influences anterior-posterior (AP) translation of medial and lateral femoral condyle during knee flexion, with greater lateral condyle AP translation seen with the Attune® TKA implant when compared to the PFC Sigma® TKA implant, which may affect tibiofemoral kinematics and influence contact stresses.29
Knee alignment can affect contact stresses between the femoral condyle and insert. Suh et al.21 in an FE analysis on the effect of varus and valgus malalignment on contact stresses in a cruciate-substituting, fixed-bearing TKR implant, reported greater total contact stress in the varus alignment than in the valgus. These findings were different from the findings of the current study where varus and valgus alignments (2.5° and 5°) were similar in terms of maximum contact stresses and percentage increase in contact stress. Contact stress patterns varied with activities of daily living such as standing, walking, and stair climbing which involved change in the knee flexion angles. In the current study, maximum contact stresses were higher during walking and standing, especially in neutral and varus alignments, when compared to stair climbing. This finding has been confirmed by a study by Song et al.30 who reported higher contact stresses in the medial compartment with knee extension.
4.1 Limitations in this study
First, the tibial tray and insert were fully bonded in this FE model and micromotions which may occur between the tibial tray and the PE insert were not considered and analysed in this study. Second, the computational model was developed using data from a young male subject and the results of the current study needs to be validated using more subjects with a wider age profile. Finally, the current study determined the effect of mechanical alignment of the knee on contact stresses and did not analyse the effect of kinematic alignment on contact stresses in both TKA models.
5 Conclusions
In conclusion, in a well aligned knee the maximum contact stress was higher in the Attune® TKA implant during standing, walking and stair climbing when compared to the PFC Sigma® TKA implant. However, in a malaligned knee (5° varus or valgus alignment), the maximum contact stress was higher in Attune® knee during standing and walking, and higher in the PFC Sigma® knee during stair climbing. Our results indicate that the newer Attune® design may be associated with higher maximum contact stresses at the femoral condyle-insert interface even in the absence of malalignment during standing, walking, and stair climbing which may increase the risk wear and implant failure.
Funding
This project was funded by an Indian Society of Hip & Knee Surgeons (ISHKS) Research Grant (DOA/13-02-2017).
References
- How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. Lancet. 2019;393(10172):655-663.
- [Google Scholar]
- Intermediate and long-term quality of life after total knee replacement: a systematic review and meta-analysis. J Bone Joint Surg Am. 2015;97(2):156-168.
- [Google Scholar]
- Failure after modern total knee arthroplasty: a prospective study of 18,065 knees. J Arthroplasty. 2018;33(2):407-414.
- [Google Scholar]
- Total knee arthroplasty at 15-17 years: does implant design affect outcome? Int Orthop. 2014;38(2):235-241.
- [Google Scholar]
- The registries: what do they tell us about knee arthroplasty? A narrative review of six national arthroplasty registers. J Orthop Traumatol. 2021;35(1):30-38.
- [Google Scholar]
- Improved design decreases wear in total knee arthroplasty with varus malalignment. Knee Surg Sports Traumatol Arthrosc. 2014;22(11):2635-2640.
- [Google Scholar]
- Impact of tibial baseplate malposition on kinematics, contact forces and ligament tensions in TKA: a numerical analysis. J Mech Behav Biomed Mater. 2020;103:103564.
- [Google Scholar]
- Clinical and radiographic results of attune and PFC sigma knee designs at 2-year follow-up: a prospective matched-pair analysis. J Arthroplasty. 2017;32(2):431-436.
- [Google Scholar]
- The evolution of implant design decreases the incidence of lateral release in primary total knee arthroplasty. J Arthroplasty. 2017;32(5):1505-1509.
- [Google Scholar]
- A comparison of clinical- and patient-reported outcomes of the cemented ATTUNE and PFC sigma fixed bearing cruciate sacrificing knee systems in patients who underwent total knee replacement with both prostheses in opposite knees. J Orthop Surg Res. 2018;13(1):54.
- [Google Scholar]
- Mid-term results show no significant difference in postoperative clinical outcome, pain and range of motion between a well-established total knee arthroplasty design and its successor: a prospective, randomized, controlled trial. Knee Surg Sports Traumatol Arthrosc. 2021;29(3):827-831.
- [Google Scholar]
- Early experience with the ATTUNE total knee replacement system. Acta Biomed. 2019;90(12-S):98-103.
- [Google Scholar]
- Modern cemented total knee arthroplasty design shows a higher incidence of radiolucent lines compared to its predecessor. Knee Surg Sports Traumatol Arthrosc. 2019;27(4):1148-1155.
- [Google Scholar]
- Technical Note: early tibial loosening of the cemented ATTUNE knee arthroplasty - just a question of design? Knee. 2021;30(4):170-175.
- [Google Scholar]
- Unusually high rate of early failure of tibial component in ATTUNE total knee arthroplasty system at implant-cement interface. J Knee Surg. 2017;30(5):435-439.
- [Google Scholar]
- A randomized controlled trial comparing tibial migration of the ATTUNE cemented cruciate-retaining knee prosthesis with the PFC-sigma design. Bone Joint Lett J. 2020;102-B(9):1158-1166.
- [Google Scholar]
- Finite element analysis of two total knee joint prostheses. Int J Interact Des Manuf. 2013;7:91.
- [Google Scholar]
- Comparison of kinematics in cruciate retaining and posterior stabilized for fixed and rotating platform mobile-bearing total knee arthroplasty with respect to different posterior tibial slope. BioMed Res Int. 2018;2018:5139074.
- [Google Scholar]
- Computational study on the effect of malalignment of the tibial component on the biomechanics of total knee arthroplasty: a Finite Element Analysis. Bone Joint Res. 2017;6(11):623-630.
- [Google Scholar]
- Mechanical properties of the posterolateral structures of the knee. Am J Sports Med. 2005;33(9):1386-1391.
- [Google Scholar]
- Comparative analysis of the structural properties of the collateral ligaments of the human knee. J Orthop Sports Phys Ther. 2012;42(4):345-351.
- [Google Scholar]
- Simulation of a knee joint replacement during a gait cycle using explicit finite element analysis. J Biomech. 2002;35(2):267-275.
- [Google Scholar]
- Influence of post-cam design on stresses on posterior-stabilized tibial posts. Clin Orthop Relat Res. 2006;450(9):150-156.
- [Google Scholar]
- Post-cam design and contact stress on tibial posts in posterior-stabilized total knee prostheses: comparison between a rounded and a squared design. J Arthroplasty. 2017;32(12):3757-3762.
- [Google Scholar]
- Effect of geometric variations on tibiofemoral surface and post-cam design of normal knee kinematics restoration. J Exp Orthop. 2018;5(1):53.
- [Google Scholar]
- The influence of total knee arthroplasty geometry on mid-flexion stability: an experimental and finite element study. J Biomech. 2013;46(7):1351-1357.
- [Google Scholar]
- Videofluoroscopic evaluation of the influence of a gradually reducing femoral radius on joint kinematics during daily activities in total knee arthroplasty. J Arthroplasty. 2020;35(10):3010-3030.
- [Google Scholar]
- Comparison of the contact stress between the sensor and real polyethylene insert in total knee arthroplasty: a finite element analysis. Ann Transl Med. 2020;8(21):1424.
- [Google Scholar]