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Computer-based analysis of different component positions and insert thicknesses on tibio-femoral and patello-femoral joint dynamics after cruciate-retaining total knee replacement
Corresponding author at: Department of Orthopaedics, Rostock University Medical Center, Doberaner Straße 142, 18057 Rostock, Germany. Fax: +49 381 494 9308.
Aesculap AG, Research and Development, Tuttlingen, GermanyLudwig Maximilians University Munich, Department of Orthopaedic Surgery, Physical Medicine and Rehabilitation, Campus Grosshadern, Munich, Germany
Positioning of the implant components and tibial insert thickness constitute critical aspects of total knee replacement (TKR) that influence the postoperative knee joint dynamics. This study aimed to investigate the impact of implant component positioning (anterior-posterior and medio-lateral shift) and varying tibial insert thickness on the tibio-femoral (TF) and patello-femoral (PF) joint kinematics and contact forces after cruciate-retaining (CR)-TKR.
Method
A validated musculoskeletal multibody simulation (MMBS) model with a fixed-bearing CR-TKR during a squat motion up to 90° knee flexion was deployed to calculate PF and TF joint dynamics for varied implant component positions and tibial insert thicknesses. Evaluation was performed consecutively by comparing the respective knee joint parameters (e.g. contact force, quadriceps muscle force, joint kinematics) to a reference implant position.
Results
The PF contact forces were mostly affected by the anterior-posterior as well as medio-lateral positioning of the femoral component (by 3 mm anterior up to 31 % and by 6 mm lateral up to 14 %). TF contact forces were considerably altered by tibial insert thickness (24 % in case of + 4 mm increase) and by the anterior-posterior position of the femoral component (by 3 mm posterior up to 16 %). Concerning PF kinematics, a medialised femoral component by 6 mm increased the lateral patellar tilt by more than 5°.
Conclusions
Our results indicate that regarding PF kinematics and contact forces the positioning of the femoral component was more critical than the tibial component. The positioning of the femoral component in anterior-posterior direction on and PF contact force was evident. Orthopaedic surgeons should strictly monitor the anterior-posterior as well as the medio-lateral position of the femoral component and the insert thickness.
In case of advanced knee osteoarthritis, total joint replacements constitute the gold standard surgical option for the patient. Despite improvements in surgical treatment and TKR technology, the rate of unsatisfied patients after total knee replacement (TKR) remains up to 20 % at a high level [
Laubach M, Hellmann JT, Dirrichs T, Gatz M, Quack V, Tingart M et al. Anterior knee pain after total knee arthroplasty: A multifactorial analysis. J Orthop Surg (Hong Kong) 2020; 28(2): 2309499020918947. https://doi.org/10.1177/2309499020918947.
]. Due to the large number of intraoperative parameters in terms of positioning, optimal TKR implantation is difficult to achieve; however, medio-lateral and anterior-posterior positioning of tibial and femoral component as well as tibial insert thickness have been demonstrated to affect the dynamics of the patello-femoral (PF) and tibio-femoral (TF) compartments as well as their interplay [
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
]. While surgical instrumentation and navigation are designed to optimise the positioning of the implant components to the patient's anatomy, the surgeon has several options to change the implant position to improve the knee joint mechanics intraoperatively.
In this context, it has been shown that the rotational and sagittal alignment and translational positioning of the implant components affect the total knee joint dynamics and contribute to postoperative pain, polyethylene wear, anterior knee pain, and increased TF loading [
Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure.
Effect of surgical parameters on the biomechanical behaviour of bicondylar total knee endoprostheses - A robot-assisted test method based on a musculoskeletal model.
Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty.
]. Clinically, some cruciate-retaining (CR)-TKR designs were observed to show pronounced paradoxical femoral anterior translation relative to the tibia during knee flexion, which can lead to increased PF loading and, ultimately, postoperative complications [
Videofluoroscopic Evaluation of the Influence of a Gradually Reducing Femoral Radius on Joint Kinematics During Daily Activities in Total Knee Arthroplasty.
] revealed that internal rotation of the tibial component significantly increased the retropatellar contact pressure. Other biomechanical studies have analysed various mechanical aspects of patellar maltracking [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
] showed that medio-lateral positioning of the femoral component significantly influenced the postoperative outcomes in terms of anterior knee pain and satisfaction after TKR, i.e., a more medial position led to less anterior knee pain.
One important design factor in TKR is the tibial insert thickness, whose contribution to the postoperative failure of TKRs has not been fully understood so far [
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
], there is a need for systematic analyses showing the effect of a 1 mm increment of tibial insert thickness in CR-TKR. However, the selection of under- or oversized polyethylene inserts, as is common in TKR [
Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty.
], might lead to an unfavourable thickness that severely influences the resulting TF kinematics, joint contact pressure, wear properties and survivorship of the implants [
] showed that the failure rates for patients with inserts of 14 mm or less was 0.7 % and for patients with inserts of 16 mm or higher was 2.3 %. Regarding the implant positioning, Steinbrueck et al. [
] showed that medio-lateral positioning of the tibial and femoral component affected the PF contact forces and kinematics after CR-TKR using a dynamic knee rig simulator on eight fresh frozen cadavers. They found that medialisation or lateralisation by 3 mm of the femoral component shifted and tilted the patella in the same direction but did not significantly increase the PF pressure and may not be clinically relevant to anterior knee pain [
], it was detected that 6 mm medialisation of the tibial component affected the ligament tension by more than 99 %. Concerning the tibial component, Didden et al. [
] deployed a knee simulator and showed that anterior positioning of the tibial component was associated with increased PF joint pressure; in contrast, the PF contact force decreased by 2.2 % for each additional millimetre of a posterior position of the tibial component.
These studies contributed to a better understanding of the positioning of implant components from a biomechanical point of view. However, there is a lack of studies that comprehensively analyse the biomechanical impact of the implant component positioning and tibial insert thickness on total knee joint dynamics and the resulting implications on TKR components and patient outcome [
]. Moreover, cadaver studies bear practical limitations: specimens’ decay thus restricts the time for analysis, different implant configurations require bone cuts making a systematic and comprehensive analysis of different TKR positions difficult, the early-flexion range is often not considered due to stability issues, and active muscle forces are usually not considered. Additionally, experimental and clinical studies could not directly separate the effect of implant positions from other parameters, showing that a systematical and reproducible analysis of intraoperative parameters under the same conditions is required. Finally, the research data were captured deploying different methods, patient geometries, and implant designs, making it difficult to compare different study data systematically. To overcome these limitations, computational models have shown significant merits and have also been proven to generate realistic results in accordance with in vivo data [
Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty.
Comparison of the biomechanical effect of posterior condylar offset and kinematics between posterior cruciate-retaining and posterior-stabilized total knee arthroplasty.
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
] during a dynamic squatting activity, the aim of our present study was to investigate the impact of implant component positioning (anterior-posterior and medio-lateral shift) and the tibial insert thickness on TF as well as PF kinematics and contact forces after bicondylar CR-TKR under systematic and reproducible conditions.
2. Materials and methods
2.1 Musculoskeletal multibody simulation model of the knee joint
Within this study, we used a previously described and validated musculoskeletal multibody simulation (MMBS) model of the lower right extremity [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
]. We computationally reconstructed the 3D bone segments (pelvis, femur, patella, tibia, fibula, and pes) as well as the implant component geometries (femoral component, patellar button, tibial insert, and tibial tray), which were then implemented into the kinematic chain of the right lower extremity [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
Briefly, the implant and bone geometries were implemented based on the medical imaging data of a male patient who received an instrumented CR-TKR due to primary osteoarthritis. The data was released as part of the 4th Grand Challenge Competition To Predict In Vivo Knee Loads [
]. This dataset consists of an 88-year-old male patient (height = 168 cm, weight = 66.7 kg) who received an instrumented CR-TKR (P.F.C. Sigma, DePuy Synthes, Raynham, MA, U.S.A.) for its implantation into the right knee [
], comprising capsular soft tissue structures around TF and PF joint included in the right knee. The force exerted by the ligament bundles was assumed to be quadratic at low strains and linear at high strains [
]. Precisely, we implemented the posterior cruciate ligament (PCL), medial collateral ligament (MCL), lateral collateral ligament (LCL), oblique popliteal ligament (OPL), lateral part of the arcuate popliteal ligament (APL), posterior capsule (pCAP) as medial and lateral part, medial patellofemoral ligament (MPFL), lateral patellofemoral ligament (LPFL), and the patellar ligament (PL). The patellar ligament (PL) was modelled as a rigid coupling element between apex patellae and tuberositas tibiae with a fixed length [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
The posterolateral attachments of the knee: a qualitative and quantitative morphologic analysis of the fibular collateral ligament, popliteus tendon, popliteofibular ligament, and lateral gastrocnemius tendon.
] and verified by an experienced orthopaedic surgeon. Note that the anterior cruciate ligament was not modelled since it was resected during the TKR surgery. The muscles of the lower extremity were divided into several structural elements based on the size of the anatomical attachment area as described in Carbone et al. [
Within an inverse kinematic analysis, the experimentally obtained motion trajectories of reflective skin markers from motion capturing were used to derive the generalised coordinates in the joint space. An inverse dynamics analysis coupled with a variant of the computed muscle control algorithm [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
]. As the knee joint consists of two complex articulating compartments, the TF and PF joints were modelled with six degrees of freedom each by means of a polygon contact model (PCM) [
]. This algorithm for contact interaction between complex geometries in multibody dynamics is based on the representation of the articulating contacting body surfaces by polygon meshes. The accompanying contact force determination is based on the elastic foundation theory [
]. For this, the geometries of the virtually implanted femoral, tibial, and patellar components of the patient’s TKR were represented by triangulated polygon meshes using the software Geomagic Studio (v.2013, 3D Systems, Rock Hill, SC, USA) to enable homogenous distribution. First, the PF joint was modelled using the PCM [
], representing the articulation between the femoral component and the medial as well as lateral tibial component for physiological-like roll-glide kinematics. In this manner, the resulting dynamics of the TF and PF joint depend on the forces exerted by the articulating surface contact of the implant components, soft tissues, muscles, and skeletal system. Finally, the MMBS model (Figure 1-A-C) with the distributed contact conditions of the TF and PF joint compartments was implemented using the multibody software environment SIMPACK (V9.7, Dassault Systèmes Deutschland GmbH, Gilching, Germany). To predict the muscle forces of the squat motion, the computed muscle control algorithm with static optimisation was implemented in MATLAB/Simulink® (v8.1, 2013a, The MathWorks Inc., Natick, MA, USA) and connected with the MMBS model in SIMPACK as part of a co-simulation [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
during the dynamic squat motion was based on experimentally obtained motion capturing during squatting activity with a posterior cruciate-retaining total knee replacement
(A). Kinematics of the implant components indicating the femoral rollback at selected knee flexion angles during the squat motion. Note that the ligament and muscle structures were not depicted for the sake of clarity (B). The musculoskeletal multibody model consists of bones, muscles, ligaments, and implanted total knee replacement in the right knee joint (C). Based on this model, the implant components were modified based on the coordinate systems for the medio-lateral (ml) and anterior-posterior (ap) positioning of the femoral and tibial components as well as the variation of the tibial insert thickness t (D).
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
], where the predicted TF contact forces were compared against the in vivo knee forces that were measured using the telemetric CR-TKR (same design as in our model) from the experimental squat trials [
]. Briefly, the successfully validated MMBS model closely captured the overall pattern and timing of the in vivo measured TF contact force. Additionally, the TF and PF kinematics and quadriceps force were compared with previous studies [
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
], depending on the penetration of the articulating implant surfaces (Figure 2-A).
Figure 2Depiction of the patello-femoral and tibio-femoral contact force (A). Evaluation of patello-femoral (B) and tibio-femoral (C) kinematics with respect to the defined coordinate systems [
]. Depiction of the femur coordinate system fi, tibia coordinate system ti and patellar coordinate system pi. Note that the muscle structures were not depicted for the sake of clarity.
]. Accordingly, a Cartesian coordinate system was established in the femoral bone fi, with the origin at the border of the intercondylar notch. The patellar Cartesian coordinate system pi was generated based on anatomical landmarks, which comprise the most medial and lateral as well as the most proximal and distal points of the patellar bone. The origin was placed at the volumetric centre of the patella and aligned to the femoral coordinate system (Figure 2-B). For this, a Cartesian coordinate system fi was established, with the mechanical axis and the origin at the centre of the transepicondylar axis (Figure 2-C). TF kinematics were defined as relative translations (medial–lateral, anterior-posterior) and rotation (internal-external). Consequently, PF kinematics were defined as relative translations (medial–lateral shift) and rotations (medial–lateral tilt, medial–lateral rotation) of the patellar coordinate system with respect to the femur-fixed coordinate system.
2.4 Analysis of different implant component positions and tibial insert thicknesses
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
]. Based on this reference, a comprehensive parameter study on different translational implant positions and tibial insert thicknesses was conducted to evaluate the impact on TF and PF contact forces and kinematics (Figure 3).
Figure 3Depiction of the implant components of the virtually implanted posterior cruciate-retaining total knee replacement (A). The entirety of different implant positions and insert thicknesses is depicted in (B): positioning of the femoral and tibial component (anterior-posterior and medio-lateral shift) as well as different tibial insert thicknesses (t).
The position of the implant components was changed based on the above described coordinate systems. For instance, the medio-lateral positioning was varied by medial or lateral translation of the centre of the implant components along the medio-lateral axis, defined as fixed to the bone geometry. In the following, different implant positions and tibial insert thicknesses were analysed (compared with the reference configuration), i.e. positioning of the femoral and tibial component in medio-lateral (m-l) by ± 3 mm and ± 6 mm and anterior-posterior (a-p) direction by ± 3 mm direction (Figure 3). Furthermore, the thickness (t) of the tibial insert was also varied by increasing the thickness of the reference configuration using an increment size of 1 mm (t = 12–16 mm). According to the database, the patient was originally treated using t = 12 mm (reference configuration). The values for each parameter (Figure 3-C) were systematically varied based on values reported from clinical [
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
] studies. Each of the implant variations used for the simulation trials was approved by an experienced orthopaedic surgeon.
In order to evaluate the resulting impact of different implant component positions and tibial insert thicknesses on total knee joint dynamics, the following joint parameters were finally calculated: PF contact force, TF contact force, and the force of the musculus quadriceps femoris. Concerning joint kinematics, the TF internal-external rotation, medio-lateral, and anterior-posterior translation as well as the patellar shift, tilt, and rotation were evaluated. The impact of each parameter variation was evaluated with respect to the reference configuration as a function of the knee flexion angle. All MMBS were performed on an off-the-shelf computer (Intel® Xeon E5-1650 v4 CPU @3.60 GHz, 32 GB RAM).
3. Results
For all simulations, similar anterior-posterior translation was observed with an anterior femoral sliding during low flexion angles up to 35°, followed by an increased posterior femoral translation with increasing flexion. Although results were evaluated for all described implant variations, only the most important findings are reported here.
3.1 Effects of different implant positions and insert thicknesses on tibio- and patello-femoral kinetics and kinematics
Medialisation or lateralisation of the implant components caused only minor changes in the TF contact force and quadriceps force (Figure 4-A1-B1, A3-B3). Concerning the PF contact force, only the medio-lateral position of the femoral component showed an effect, i.e., a 6 mm medialised femoral component decreased the PF contact force up to 10 % at 90° knee flexion (Figure 4-A2). Contrarily, lateralisation of the femoral component by 6 mm increased the PF contact force by up to 14 % at 90° knee flexion. The tibial insert thickness (+4 mm) increased the TF contact force by up to 24 % at 90° knee flexion. Contrarily, the PF contact force decreased by up to 11.5 %, and the quadriceps force decreased by up to 11 % (Figure 4-C1-C3).
Figure 4Effects of the medio-lateral positioning of the femoral component (A1-A3) and tibial component (B1-B3) as well as the variation of the tibial insert thickness (C1-C3) on the tibio-femoral and patello-femoral kinetics. Impact of the medio-lateral positioning of the implant components (tibial and femoral component) and varying tibial insert thickness on the tibio-femoral contact force (A1, B1, and C1), patellofemoral contact force (A2, B2, and C2), and quadriceps force (A3, B3, and C3). Note that the occurrence of the maximum absolute deviations is depicted as black diamonds.
The anterior-posterior positioning of the femoral component influenced the PF dynamics (Figure 5): the anterior position considerably increased the PF contact force by 31 % at 60° knee flexion (1656 N), and the posterior position was associated with lower PF contact forces (979 N) by 23 % at 60° knee flexion (Figure 5-A2). In contrast, the TF contact force showed an opposite behaviour in the anterior-posterior position of the femoral component, e.g., a posterior position yielded an increase of the TF contact force by up to 16 % at 60° knee flexion (Figure 5-A1). For all simulations, the force of the musculus quadriceps femoris was increased during knee flexion and only affected by the anterior-posterior position of the femoral component with an increase by 15 % at 90° knee flexion in case of 3 mm anterior translation (Figure 5-A3 black diamond purple dotted line).
Figure 5Effects of the anterior-posterior positioning of the femoral component (A1-A3) and tibial component (B1-B3) on the tibio-femoral and patello-femoral kinetics. Impact of the anterior-posterior positioning of the implant components (tibial and femoral component) on the tibio-femoral (A1, B1), patellofemoral contact force (A2, B2), and the quadriceps force (A3, B3). Note that the occurrence of the maximum absolute deviations is depicted as black diamonds.
Concerning the TF kinematics, medialisation of the tibial component slightly increased the posterior translation and the internal rotation (Figure 6-B2, B3). The medio-lateral position of the tibial component shifted the tibia in the opposite direction, e.g., a lateralised tibial component resulted in a more medial shift of the tibia and vice versa.
Figure 6Effects of the medio-lateral positioning of the femoral (A1-A3) and tibial component (B1-B3) as well as the variation of the tibial insert thickness (C1-C3) on the tibio-femoral kinematics. Impact of the medio-lateral positioning of the implant components (tibial and femoral component) and varying tibial insert thickness on the tibial medio-lateral translation (A1, B1, and C1), femoral anterior-posterior translation (A2, B2, and C2), and tibial internal-external rotation (A3, B3, and C3). Note that the occurrence of the maximum absolute deviations is depicted as black diamonds.
Although the PF dynamics remained almost unchanged in the case of the medio-lateral position of the tibial component, there was a substantial difference in PF kinematics regarding patellar tilt and rotation (Figure 7-B2, B3). In the case of the femoral component, medialisation and lateralisation led to an alteration in the patellar shift, tilt, and rotation. The 6 mm lateral position considerably increased the lateral patellar shift by more than 6 mm (Figure 7-A1) during knee flexion. Consequently, the patella was also tilted and rotated in the same direction after the medio-lateral position of the femoral and tibial component (Figure 7-A2, B2, A3, B3). A medial position of the femoral component by 6 mm increased the patellar tilt by more than 5° at 90° knee flexion (Figure 7-A2).
Figure 7Effects of the medio-lateral positioning of the femoral (A1-A3) and tibial component (B1-B3) as well as the variation of the tibial insert thickness (C1-C3) on the patello-femoral kinematics. Impact of the medio-lateral positioning of the implant components (tibial and femoral component) and varying tibial insert thickness on the patellar shift (A1, B1, and C1), patellar tilt (A2, B2, and C2), and patellar rotation (A3, B3, and C3). Patellar tilt: + indicates medial patellar tilt; − indicates lateral patellar tilt. Note that the occurrence of the maximum absolute deviations is depicted as black diamonds.
Concerning the anterior-posterior position (Figure 8), a more posterior position of the femoral component was associated with increased femoral rollback by more than 3.5 mm at 90° knee flexion compared to the reference and led to an earlier occurrence of rollback (25° knee flexion) compared to the reference configuration (35° knee flexion).
Figure 8Effects of the anterior-posterior positioning of the femoral (A1-A3) and tibial component (B1-B3) on the tibio-femoral kinematics. Impact of the anterior-posterior positioning of the implant components (tibial and femoral component) on the tibial medio-lateral translation (A1, B1), femoral anterior-posterior translation (A2, B2), and tibial internal-external rotation (A3, B3). Note that the occurrence of the maximum absolute deviations is depicted as black diamonds.
Anterior-posterior position of the tibial component only had a minor influence on PF kinematics (Figure 9-B1-B3). However, a posterior position of the femoral component led to a considerable influence on patellar tilt and rotation, e.g., a more posterior position of the femoral component increased the lateral patellar tilt by almost 5° at 30° knee flexion (Figure 9-A2).
Figure 9Effects of the anterior-posterior positioning of the femoral (A1-A3) and tibial component (B1-B3) on the patellofemoral kinematics. Impact of the anterior-posterior positioning of the implant components (tibial and femoral component) on the patellar shift (A1, B1), patellar tilt (A2, B2), and patellar rotation (A3, B3). Patellar tilt: + indicates medial patellar tilt; − indicates lateral patellar tilt. Note that the occurrence of the maximum absolute deviations is depicted as black diamonds.
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
] on total knee joint dynamics. The most important finding of this study was that the characterisation of kinematics and kinetics in both knee joint compartments during a squat motion for the investigated CR-TKR mainly depends on the anterior-posterior and medio-lateral positioning of the femoral component and varying tibial insert thickness. Despite the high success rates in the current practice of TKR surgery and the implant design used (P.F.C. Sigma CR) [
Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure.
] reported that patients still have pain during the squat movement after TKR. In our study, we identified some potential factors that may explain the risk of anterior knee pain. In line with previous studies [
], our results of the investigated total knee implant showed a paradoxical femoral anterior translation relative to the tibia during early knee flexion, which was also clinically observed and can lead to increased PF loading [
Videofluoroscopic Evaluation of the Influence of a Gradually Reducing Femoral Radius on Joint Kinematics During Daily Activities in Total Knee Arthroplasty.
Laubach M, Hellmann JT, Dirrichs T, Gatz M, Quack V, Tingart M et al. Anterior knee pain after total knee arthroplasty: A multifactorial analysis. J Orthop Surg (Hong Kong) 2020; 28(2): 2309499020918947. https://doi.org/10.1177/2309499020918947.
]. At the same time, studies have shown that lower forces of the musculus quadriceps femoris and PF contact force can contribute to reduce anterior knee pain [
Laubach M, Hellmann JT, Dirrichs T, Gatz M, Quack V, Tingart M et al. Anterior knee pain after total knee arthroplasty: A multifactorial analysis. J Orthop Surg (Hong Kong) 2020; 28(2): 2309499020918947. https://doi.org/10.1177/2309499020918947.
In this context, we observed that loading of the retro-patellar joint compartment was mostly affected by the anterior-posterior (by 3 mm anterior increased up to 31 %) and medio-lateral positioning (by 6 mm lateral increased up to 14 %) of the femoral component. The higher PF contact forces could lead to an overload of the PF joint and anterior knee pain [
] showed that patients with a femoral shield anterior to the cortex showed a significantly worse outcome than patients with neutral or posterior positioning. Although a 3 mm posterior position of the femoral component decreased the PF contact forces by 22 % in our study, this position also led to an abnormal patellar tracking, which may cause further clinical problems. For instance, a posterior positioning of the femoral component can lead to a femoral notching, which is associated with a higher risk of periprosthetic bone fracture [
Anterior femoral notching ≥ 3 mm is associated with increased risk for supracondylar periprosthetic femoral fracture after total knee arthroplasty: a systematic review and meta-analysis.
] showed that a more medial position of the femoral component results in less postoperative pain, which could be explained with our results showing lower PF contact forces by up to 10 % for a medialised femoral component for the same implant. Conversely, Steinbrueck et al. [
] found no significant influence of medio-lateral femoral component positioning on PF contact pressure but only investigated component displacements of ± 3 mm, while we observed differences in PF contact forces for displacements of ± 6 mm. Considering the medial tracking of the patella after TKR [
], a medial positioning of the femoral component could lead to an optimal tracking in the trochlear groove. The TF contact forces were considerably increased by the tibial insert thickness (up to 24 % in case of + 4 mm increase) and the posterior positioning of the femoral component (by 3 mm posterior up to 16 %). Contrarily, a thicker tibial insert yielded a reduced PF contact force by up to 11.5 %, while the required quadriceps force to perform the squat movement decreased by up to 11 %. These results may explain why thicker tibial inserts reduce the potential risk of anterior knee pain in line with previous studies [
] reported a higher revision rate with thicker tibial inserts, which could be explained with the higher TF force and thus loading of the implant components. Furthermore, our results demonstrated that variations in the medio-lateral and anterior-posterior direction of the femoral component had a considerably larger impact on PF contact force, quadriceps force, femoral anterior-posterior translation, and patellar tracking than corresponding variations in the tibial component.
The findings emphasised the impact of the implant component’s positions alongside the anterior-posterior direction, especially for the femoral component, which is in agreement with prior studies [
]. For instance, the force of the musculus quadriceps femoris was increased in the case of the anterior positioning of the femoral component, which often leads to a reduced flexion angle, as previously described [
]. This can be explained by the higher contact forces resulted from the anteriorly shifted centre of rotation of the knee, which can lead to a decreased moment arm and thus to an increased quadriceps force. TF contact forces, on the contrary, had only a minor effect and decreased with an increase in the anterior positioning of the femoral component. Nevertheless, a more posterior position of the tibial component slightly decreased the PF contact forces, which is in agreement with the results reported by Didden et al. [
]. This discrepancy can be attributed to the experimental setup, where the mechanical behaviour of the muscle structures, PF ligaments and contact surfaces are highly influential to the results and further stress the importance of maintaining these structures in biomechanical models. Therefore, the differences may have been caused by the experimental approach of Didden et al. [
], where the muscle structures and PF ligaments were emulated with cables in a knee rig.
Medialisation and lateralisation of the implant components did also impact the femoral anterior-posterior translation, which is in agreement with the computational study by Fottner et al. [
]. As the medialisation or lateralisation of the tibial component had no considerable impact on PF contact forces, it is therefore most likely not a critical factor for knee pain compared to the femoral component [
]. In our study the medio-lateral positioning of the implant components shifted and tilted the patella in the same direction, i.e. medialisation of the femoral component decreased the lateral patellar shift and increased the medial tilt of the patella, which corresponds with previous findings [
]. Compared to the femoral component, the medio-lateral positioning of the tibial component had only a minor effect on the patellar shift, which is in contrast to a previous study [
]. A possible explanation is the use of different methodologies and TKRs. Differences in the geometry of the anterior flange of the femoral component can negate other influences observed at different TKRs.
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
], no studies have addressed the effect of a 1-mm increment tibial insert thickness in CR-TKR. Our comprehensive study showed that the thickness considerably influenced TF contact forces by up to 24 % in case of + 4 mm insert thickness due to an increased tightening of the ligament structures. The thickness is, therefore, an important factor that can cause wear of polyethylene components [
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
]. Contrarily, increased insert thickness led to lower PF contact forces. This can be explained with the accompanying decrease in internal rotation of the TF joint in the mid-flexion range during squatting and the increased femoral rollback, which is in good agreement with previous studies [
Besides experimental and clinical studies, one advantage of our present computer-based study is the use of the MMBS model with a detailed knee joint and the representation of relevant muscles of the lower extremity, as previous studies assumed the muscles with constant loads [
Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure.
Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure.
], which may limit the applicability of our results. However, in our study, all the simulation variables were highly controlled, thus overcoming the limitations of previous experimental and clinical studies [
Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty.
]. Additional simulations to more activities (e.g., rising from a chair and walking) may be helpful in the future for a more robust investigation and to support the presented findings. Further analysis using a larger patient population and more TKR designs is needed for clinical validation. Moreover, future studies should also focus on patella morphology as the influence; e.g., the height of the patella has not yet been extensively investigated [
Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure.
]. In future studies, combined effects regarding different implant designs as well as the rotational alignment and translational positioning of the implant components will be analysed.
In conclusion, our computational study provides a better understanding of the effect of the intraoperative implant component positioning and tibial insert thickness on knee joint dynamics. For the CR-TKR design investigated, we could show that medio-lateral and anterior-posterior positioning of the femoral component has a considerable impact on TF and PF contact force and should therefore be taken with care intraoperatively as described in clinical studies. Although the posterior positioning of the femoral component was beneficial due to a decreased PF contact force, it is important to avoid excessive posterior translation due to a high influence on patellar tracking and TF loading. In this regard, the femoral component seems to constitute a more critical factor than the tibial component. While an increased insert thickness led to a reduction in PF contact and quadriceps force, TF contact force increased at the same time. Our computational model can further contribute to computer-assisted preclinical testing of TKRs and may support clinical decision-making within preoperative planning and intraoperative navigation. However, further studies are necessary to analyse the clinical consequences in terms of postoperative complications after CR-TKR.
Ethical approval
Approval was not required as human subjects and animals were not involved in this study.
Informed consent
This was not required for this study.
Funding
This research project was supported by Aesculap AG, Research and Development, Tuttlingen, Germany.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
References
Bourne R.B.
Chesworth B.M.
Davis A.M.
Mahomed N.N.
Charron K.D.J.
Patient satisfaction after total knee arthroplasty: who is satisfied and who is not?.
Laubach M, Hellmann JT, Dirrichs T, Gatz M, Quack V, Tingart M et al. Anterior knee pain after total knee arthroplasty: A multifactorial analysis. J Orthop Surg (Hong Kong) 2020; 28(2): 2309499020918947. https://doi.org/10.1177/2309499020918947.
A Current Prosthesis With a 1-mm Thickness Increment for Polyethylene Insert Could Result in Fewer Adjustments of Posterior Tibial Slope in Cruciate-Retaining Total Knee Arthroplasty.
Is there a biomechanical explanation for anterior knee pain in patients with patella alta?: influence of patellar height on patellofemoral contact force, contact area and contact pressure.
Effect of surgical parameters on the biomechanical behaviour of bicondylar total knee endoprostheses - A robot-assisted test method based on a musculoskeletal model.
Flexing and downsizing the femoral component is not detrimental to patellofemoral biomechanics in posterior-referencing cruciate-retaining total knee arthroplasty.
Videofluoroscopic Evaluation of the Influence of a Gradually Reducing Femoral Radius on Joint Kinematics During Daily Activities in Total Knee Arthroplasty.
Musculoskeletal Multibody Simulation Analysis on the Impact of Patellar Component Design and Positioning on Joint Dynamics after Unconstrained Total Knee Arthroplasty.
Comparison of the biomechanical effect of posterior condylar offset and kinematics between posterior cruciate-retaining and posterior-stabilized total knee arthroplasty.
The posterolateral attachments of the knee: a qualitative and quantitative morphologic analysis of the fibular collateral ligament, popliteus tendon, popliteofibular ligament, and lateral gastrocnemius tendon.
Anterior femoral notching ≥ 3 mm is associated with increased risk for supracondylar periprosthetic femoral fracture after total knee arthroplasty: a systematic review and meta-analysis.
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