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The Effect of Tibial Slope on the Biomechanics of Cruciate-Retaining TKA: a Musculoskeletal Simulation Study

Abstract

INTRODUCTION: Tibial slope can affect the outcomes of Total Knee Arthroplasty (TKA). More posterior slope potentially helps releasing a too tight flexion gap and it is generally associated with a wider range of post-operative knee flexion. However, the mechanism by which tibial slope affects the function of TKA during dynamic activities of daily living is rather complex and not well documented. The aim of this study was to investigate the effect of tibial slope on the kinematics of the tibiofemoral (TF) contact point, quadriceps muscle forces, and patellofemoral (PF) joint contact forces during squat. In addition, we studied the effect of anterior tibial cortex-referencing (ACR) versus center of tibial plateau-referencing (CPR), as two possible techniques to obtain the desired degree of tibial slope. METHODS: A previously validated musculoskeletal model of a 86-year-old male subject, having a cruciate-retaining (CR) TKA prosthesis, was used to simulate a squat activity [1]. Motion-capture data were input to a motion optimization algorithm to find the full body kinematics. Quadriceps muscle forces were then calculated using inverse-dynamics. The kinematics of the TF contact point and PF joint contact forces were simultaneously calculated using force-dependent kinematics. A baseline case with 0° tibial slope was simulated, plus four additional cases with anterior (-3°), and posterior (+3°, +6°, +9°) tibial slope using the ACR technique (Fig. 1a), and four using the CPR technique (Fig. 1b). RESULTS: Compared to the baseline, more posterior tibial slope with ACR technique resulted in a larger excursion of the TF contact point, which shifted to a more anterior position, on the lateral side, and a more posterior position, on the medial side, in extension (Fig. 2). With the CPR technique, the contact point in extension shifted gradually more posterior on both sides with more posterior slope, and in flexion it shifted gradually more posterior mainly on the lateral side. The peak quadriceps force decreased on average by 1.7 and 1.2 % BW per degree of more posterior slope, with the ACR and CPR techniques, respectively. However, due to the different relative position of patella and femur, the peak PF contact force was mainly reduced by increasing the posterior slope with the CPR technique (-3.9 % BW/degree), rather than with the ACR technique (-1.5 % BW/degree) (Fig. 3). DISCUSSION: Increasing the tibial slope using the ACR technique produced large changes in the TF kinematics: the pattern of the contact point became more unstable, with a larger AP movement observed on the lateral side, denoting increased anterior-posterior laxity. On the other hand, variations of tibial slope with CPR technique resulted in more stable TF kinematics, more posterior position of the TF contact point, and a greater reduction of the PF contact forces. It is advisable to pre-plan the desired amount of tibial slope and execute it using the CPR technique. The surgeon should be very careful applying too much tibial slope with the ACR technique in CR-TKA, as it may have devastating effects on the TF kinematics, laxity and PF forces. SIGNIFICANCE: This study provides new insights into the effect of variation of tibial slope in TKA using different surgical techniques, which were not documented before, and used a highly controlled and parameterized study design and dynamic loading conditions. Orthopedic surgeons can directly use these results as an indication for the clinical practice. The presented tool can also be very useful for educational/medical training purposes. REFERENCES: [1] Marra MA, Vanheule V, Fluit R, et al. A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of Total Knee Arthroplasty. ASME. J Biomech Eng. 2015;137(2):020904-020904-12 ACKNOWLEDGEMENTS: The research leading to these results has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 323091 awarded to N. Verdonschot.
The Effect of Tibial Slope on the Biomechanics of Cruciate-Retaining TKA: a Musculoskeletal Simulation Study
Marco A. Marra1, Marta Strzelczak1, Petra J.C. Heesterbeek2, Sebastiaan van de Groes1, Dennis Janssen1, Bart F.J.M. Koopman3, Ate B. Wymenga2,
Nico Verdonschot1,3
1Radboudumc, Nijmegen, The Netherlands, 2Sint Maartenskliniek, Nijmegen, The Netherlands, 3University of Twente, Enschede, The Netherlands,
Disclosures: M. Marra: None. M. Strzelczak: None. P. Heesterbeek: None. S. van de Groes: None. D. Janssen: None. B. Koopman: None. A. Wymenga:
None. N. Verdonschot: None.
INTRODUCTION: Tibial slope can affect the outcomes of Total Knee Arthroplasty (TKA). More posterior slope potentially helps releasing a too tight
flexion gap and it is generally associated with a wider range of post-operative knee flexion. However, the mechanism by which tibial slope affects the
function of TKA during dynamic activities of daily living is rather complex and not well documented. The aim of this study was to investigate the effect of
tibial slope on the kinematics of the tibiofemoral (TF) contact point, quadriceps muscle forces, and patellofemoral (PF) joint contact forces during squat. In
addition, we studied the effect of anterior tibial cortex-referencing (ACR) versus center of tibial plateau-referencing (CPR), as two possible techniques to
obtain the desired degree of tibial slope.
METHODS: A previously validated musculoskeletal model of a 86-year-old male subject, having a cruciate-retaining (CR) TKA prosthesis, was used to
simulate a squat activity [1]. Motion-capture data were input to a motion optimization algorithm to find the full body kinematics. Quadriceps muscle forces
were then calculated using inverse-dynamics. The kinematics of the TF contact point and PF joint contact forces were simultaneously calculated using force-
dependent kinematics. A baseline case with 0° tibial slope was simulated, plus four additional cases with anterior (-3°), and posterior (+3°, +6°, +9°) tibial
slope using the ACR technique (Fig. 1a), and four using the CPR technique (Fig. 1b).
RESULTS: Compared to the baseline, more posterior tibial slope with ACR technique resulted in a larger excursion of the TF contact point, which shifted
to a more anterior position, on the lateral side, and a more posterior position, on the medial side, in extension (Fig. 2). With the CPR technique, the contact
point in extension shifted gradually more posterior on both sides with more posterior slope, and in flexion it shifted gradually more posterior mainly on the
lateral side. The peak quadriceps force decreased on average by 1.7 and 1.2 % BW per degree of more posterior slope, with the ACR and CPR techniques,
respectively. However, due to the different relative position of patella and femur, the peak PF contact force was mainly reduced by increasing the posterior
slope with the CPR technique (-3.9 % BW/degree), rather than with the ACR technique (-1.5 % BW/degree) (Fig. 3).
DISCUSSION: Increasing the tibial slope using the ACR technique produced large changes in the TF kinematics: the pattern of the contact point became
more unstable, with a larger AP movement observed on the lateral side, denoting increased anterior-posterior laxity. On the other hand, variations of tibial
slope with CPR technique resulted in more stable TF kinematics, more posterior position of the TF contact point, and a greater reduction of the PF contact
forces. It is advisable to pre-plan the desired amount of tibial slope and execute it using the CPR technique. The surgeon should be very careful applying too
much tibial slope with the ACR technique in CR-TKA, as it may have devastating effects on the TF kinematics, laxity and PF forces.
SIGNIFICANCE: This study provides new insights into the effect of variation of tibial slope in TKA using different surgical techniques, which were not
documented before, and used a highly controlled and parameterized study design and dynamic loading conditions. Orthopedic surgeons can directly use
these results as an indication for the clinical practice. The presented tool can also be very useful for educational/medical training purposes.
REFERENCES: [1] Marra MA, Vanheule V, Fluit R, et al. A Subject-Specific Musculoskeletal Modeling Framework to Predict In Vivo Mechanics of
Total Knee Arthroplasty. ASME. J Biomech Eng. 2015;137(2):020904-020904-12
ACKNOWLEDGEMENTS: The research leading to these results has received funding from the European Research Council under the European Union's
Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 323091 awarded to N. Verdonschot.
... 7,45,52,54 In other words, flexion improved if PCo was translated to the posterior direction and PTS increased, 7,45,55 and the quadriceps muscle and patellar tendon force and contact stress on the patellar button decreased if PTS increased. [49][50][51]56 This study showed the importance of preserving the original anatomy of the patient in TKa. although increased PTS provides good biomechanical effects, it should be moderated because it may cause knee instability. ...
Article
Objectives: Posterior condylar offset (PCO) and posterior tibial slope (PTS) are critical factors in total knee arthroplasty (TKA). A computational simulation was performed to evaluate the biomechanical effect of PCO and PTS on cruciate retaining TKA. Methods: We generated a subject-specific computational model followed by the development of ± 1 mm, ± 2 mm and ± 3 mm PCO models in the posterior direction, and -3°, 0°, 3° and 6° PTS models with each of the PCO models. Using a validated finite element (FE) model, we investigated the influence of the changes in PCO and PTS on the contact stress in the patellar button and the forces on the posterior cruciate ligament (PCL), patellar tendon and quadriceps muscles under the deep knee-bend loading conditions. Results: Contact stress on the patellar button increased and decreased as PCO translated to the anterior and posterior directions, respectively. In addition, contact stress on the patellar button decreased as PTS increased. These trends were consistent in the FE models with altered PCO. Higher quadriceps muscle and patellar tendon force are required as PCO translated in the anterior direction with an equivalent flexion angle. However, as PTS increased, quadriceps muscle and patellar tendon force reduced in each PCO condition. The forces exerted on the PCL increased as PCO translated to the posterior direction and decreased as PTS increased. Conclusion: The change in PCO alternatively provided positive and negative biomechanical effects, but it led to a reduction in a negative biomechanical effect as PTS increased.Cite this article: K-T. Kang, Y-G. Koh, J. Son, O-R. Kwon, J-S. Lee, S. K. Kwon. A computational simulation study to determine the biomechanical influence of posterior condylar offset and tibial slope in cruciate retaining total knee arthroplasty. Bone Joint Res 2018;7:69-78. DOI: 10.1302/2046-3758.71.BJR-2017-0143.R1.
Chapter
Over the past few decades, advancements in total knee arthroplasty (TKA) surgery techniques and implant design have aimed to reproduce as closely as possible the anatomy and biomechanics of the native knee. Posterior cruciate ligament-retaining (CR) TKA is the least constrained of the knee prostheses and in theory should have attained better postoperative knee proprioception, kinematics, and flexion due to retention of the posterior cruciate ligament (PCL) as compared to posterior-stabilized (PS) devices that sacrifice it. However, clinical results of CR TKA have not been shown to be consistently superior to those of PS TKA and patient perception has not appreciably improved over the past 20 years. It will be explored in this chapter whether new caliper-based kinematic alignment concepts may change the paradigm in favor of retaining the PCL. It will also focus on the importance of cementation technique in ensuring excellent longevity of cemented TKA.
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