Total Knee Replacement: Subject-Specific Modeling, Finite Element Analysis, and Evaluation of Dynamic Activities

Machine Learning Approaches for 3D Motion Synthesis and Musculoskeletal Dynamics Estimation: A Survey

The inference of 3D motion and dynamics of the human musculoskeletal system has traditionally been solved using physics-based methods that exploit physical parameters to provide realistic simulations. Yet, such methods suffer from computational complexity and reduced stability, hindering their use in computer graphics applications that require real-time performance. With the recent explosion of data capture (mocap, video) machine learning (ML) has started to become popular as it is able to create surrogate models harnessing the huge amount of data stemming from various sources, minimizing computational time (instead of resource usage), and most importantly, approximate real-time solutions. The main purpose of this paper is to provide a review and classification of the most recent works regarding motion prediction, motion synthesis as well as musculoskeletal dynamics estimation problems using ML techniques, in order to offer sufficient insight into the state-of-the-art and draw new research directions. While the study of motion may appear distinct to musculoskeletal dynamics, these application domains provide jointly the link for more natural computer graphics character animation, since ML-based musculoskeletal dynamics estimation enables modeling of more long-term, temporally evolving, ergonomic effects, while offering automated and fast solutions. Overall, our review offers an in-depth presentation and classification of ML applications in human motion analysis, unlike previous survey articles focusing on specific aspects of motion prediction.

Assessing the behavior of a hybrid model of the knee with contact surrogate under parameter uncertainties

Modeling the knee is an important factor in increasing the quality of life of both healthy individuals and patients. Nevertheless, the intricate nature of the knee makes this problem complicated. In this study, an extension to an established planar knee joint model with Hertzian contact pairs is proposed with contact mechanics based on polynomial chaos expansion surrogate. Firstly, the finite element (FE) model is made representing a contact pair of sphere-to-plane type with two layers on both bodies, corresponding to the cartilage and the bone. Five variables corresponding to both geometry and material parameters are used to parametrize this model. Then, 128 distinct variants of the FE model are created based on a quasi-Monte Carlo sequence. This dataset is used to train and validate the surrogate. The trained surrogate is proven to have predictive capabilities with an average nRMSE of 0.2% in randomized test/train splits. When included in a model of the knee and tested under parameter uncertainties in Monte Carlo simulations, it results in nRMSE of 58% for angular coordinate compared to the original model with Hertzian pair. This signifies the high influence of contact formulation on the model output and the need for more physically based models in knee contact modeling.

Computational Lower Limb Simulator Boundary Conditions to Reproduce Measured TKA Loading in a Cohort of Telemetric Implant Patients

Recent advancements in computational modeling offer opportunities to refine total knee arthroplasty (TKA) design and treatment strategies. This study developed patient-specific simulator external boundary conditions (EBCs) using a PID-controlled lower limb finite element (FE) model. Calibration of the external actuation required to achieve measured patient-specific joint loading and motion was completed for nine patients with telemetric implants during gait, stair descent, and deep knee bend. The study also compared two EBC scenarios: activity-specific hip AP motion and pelvic rotation (that was averaged across all patients for an activity) and patient-specific hip AP motion and pelvic rotation. Including patient-specific data significantly improved reproduction of joint-level loading, reducing root mean squared error between the target and achieved loading by 28.7% and highlighting the importance of detailed patient data in replicating joint kinematics and kinetics. The principal component analysis (PCA) of the EBCs for the patient dataset showed that one component represented 77.8% of the overall variation, while the first three components represented 97.8%. Given the significant loading variability within the patient cohort, this group of patient-specific models can be run individually to provide insight into expected TKA mechanics variability, and the PCA can be utilized to further create reasonable EBCs that expand the variability evaluated.

Influence of posterior cruciate ligament tension on tibiofemoral and patellofemoral joint contact mechanics in cruciate-retaining total knee replacement: a combined musculoskeletal multibody and finite-element simulation

The influence of posterior cruciate ligament (PCL) tension on the clinical outcome of cruciate-retaining total knee replacement (CR-TKR) remains controversial. Various numerical approaches have been used to study this influence systematically, but the models used are limited by certain assumptions and simplifications. Therefore, the objective of this computational study was to develop a combined musculoskeletal multibody and finite-element simulation during a squat motion to 90° knee flexion with a CR-TKR design to overcome previous limitations regarding model inputs. In addition, different PCL tensions (tight, lax, resected) were modeled and the influence on tibiofemoral and resurfaced patellofemoral joint dynamics and contact stresses was evaluated. The effect of the PCL on knee joint dynamics and contact stresses was more pronounced at higher flexion angles. Tibiofemoral joint dynamics were influenced and a tight PCL induced increased posterior femoral translation during flexion. The maximum contact stress in the tibial insert increased from 20.6 MPa to 22.5 MPa for the resected and tightest PCL at 90° knee flexion. Patellofemoral joint dynamics were only slightly affected by PCL tension. However, the maximum contact stress in the patellar component decreased from 58.0 MPa to 53.7 MPa for the resected and tightest PCL at 90° knee flexion. The combination of musculoskeletal multibody and finite-element simulation is a sufficient method to comprehensively investigate knee joint dynamics and contact stresses in CR-TKR. The PCL tension after CR-TKR affects joint dynamics and contact stresses at the articulating implant surfaces.

A novel computational workflow to holistically assess total knee arthroplasty biomechanics identifies subject-specific effects of joint mechanics on implant fixation

Computational studies of total knee arthroplasty (TKA) often focus on either joint mechanics (kinematics and forces) or implant fixation mechanics. However, such disconnect between joint and fixation mechanics hinders our understanding of overall TKA biomechanical function by preventing identification of key relationships between these two levels of TKA mechanics. We developed a computational workflow to holistically assess TKA biomechanics by integrating musculoskeletal and finite element (FE) models. For our initial study using the workflow, we investigated how tibiofemoral contact mechanics affected the risk of failure due to debonding at the implant-cement interface using the four available subjects from the Grand Challenge Competitions to Predict In Vivo Knee Loads. We used a musculoskeletal model with a 12 degrees-of-freedom knee joint to simulate the stance phase of gait for each subject. The computed tibiofemoral joint forces at each node in contact were direct inputs to FE simulations of the same subjects. We found that the peak risk of failure did not coincide with the peak joint forces or the extreme tibiofemoral contact positions. Moreover, despite the consistency of joint forces across subjects, we observed important variability in the profile of the risk of failure during gait. Thus, by a combined evaluation of the joint and implant fixation mechanics of TKA, we could identify subject-specific effects of joint kinematics and forces on implant fixation that would otherwise have gone unnoticed. We intend to apply our workflow to evaluate the impact of implant alignment and design on TKA biomechanics.

[Innovative image-based planning in musculoskeletal surgery]

BACKGROUND

For the preparation of surgical procedures in orthopedics and trauma surgery, precise knowledge of imaging and the three-dimensional imagination of the surgeon are of outstanding importance. Image-based, preoperative two-dimensional planning is the gold standard in arthroplasty today. In complex cases, further imaging such as computed tomography (CT) or magnetic resonance imaging is also performed, generating a three-dimensional model of the body region and helping the surgeon in the planning of the surgical treatment. Four-dimensional, dynamic CT studies have also been reported and are available as a complementary tool.

DIGITAL AIDS

Furthermore, digital aids should generate an improved representation of the pathology to be treated and optimize the surgeon's imagination. The finite element method allows patient-specific and implant-specific parameters to be taken into account in preoperative surgical planning. Intraoperatively, relevant information can be provided by augmented reality without significantly influencing the surgical workflow.

Stress distribution patterns during the gait cycle in patients with anterior femoral notching following total knee replacement

Background

Anterior femoral notching (AFN) is a severe complication of total knee replacement (TKR), which in a percentage of patients may lead to fractures after surgery. The purpose of this study was to investigate the stress distribution in patients with AFN and the safety depth of AFN during the gait cycle.

Methods

We performed a finite element (FE) analysis to analyse the mechanics around the femur during the gait cycle in patients with AFN. An adult volunteer was selected as the basis of the model. The TKR models were established in the 3D reconstruction software to simulate the AFN model during the TKR process, and the 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm AFN models were established, after which the prosthesis was assembled. Three key points of the gait cycle (0°, 22°, and 48°) were selected for the analysis.

Results

The stress on each osteotomy surface was stable in the 0° phase. In the 22° phase, the maximum equivalent stress at 3 mm was observed. In the 48° phase, with the increase in notch depth, each osteotomy surface showed an overall increasing trend, the stress range was more extended, and the stress was more concentrated. Moreover, the maximum equivalent force value (158.3 MPa) exceeded the yield strength (115.1 MPa) of the femur when the depth of the notch was ≥ 3 mm.

Conclusions

During the gait cycle, if there is an anterior femoral cortical notch ≥ 3 mm, the stress will be significantly increased, especially at 22° and 48°. The maximum equivalent stress exceeded the femoral yield strength and may increase the risk of periprosthetic fractures.

Superimposition of ground reaction force on tibial-plateau supporting diagnostics and post-operative evaluations in high-tibial osteotomy. A novel methodology

BACKGROUND

A fully personalised combination of Gait Analysis (GA), including Ground Reaction Force (GRF), and patient-specific knee joint morphology has not yet been reported. This can provide valuable biomechanical insight in normal and pathological conditions. Abnormal knee varus results in medial knee condylar hyper-compression and osteoarthritis, which can be prevented by restoring proper condylar load distribution via High Tibial Osteotomy (HTO).

RESEARCH QUESTION

This study was aimed at reporting on an original methodology, merging GA, GRF and Computer-Tomography (CT) to depict a patient-specific representation of the knee mechanical condition during locomotion. It was hypothesised that HTO results in a lateralized pattern of GRF with respect to the tibial plateau.

METHODS

Four patients selected for HTO received clinical, radiological and instrumental examinations, pre- and post-operatively at 6-month follow-up. GA was performed during level walking and more demanding motor tasks using a 9-camera motion-capture system, combined with two force platforms, and an established protocol. Additional skin markers were positioned around the tibial-plateau rim. Weight-bearing CT scans of the knee were collected while still wearing these markers. Proximal tibial and marker morphological models were reconstructed. The markers from CT reconstruction were then registered to the corresponding trajectories as tracked by GA data. Resulting registration matrices were used to report GRF vectors on the plane best matching the tibial-plateau model and the intersection paths were calculated.

RESULTS AND SIGNIFICANCE

The registration procedure was successfully executed, with a max registration error of about 3 mm. GRF intersection paths were found medially to the tibial plateau pre-op, and lateralized post-op, thus much closer to the knee centre, as expected after HTO. The exploitation of the present methodology offers personalised quantification of the original mechanical misalignment and of the effect of surgical correction which could enhance diagnostics and planning of HTO as well as other knee treatments.

Future Directions in Patellofemoral Imaging and 3D Modeling

PURPOSE OF REVIEW

Patellofemoral instability involves complex, three-dimensional pathological anatomy. However, current clinical evaluation and diagnosis relies on attempting to capture the pathology through numerous two-dimensional measurements. This current review focuses on recent advancements in patellofemoral imaging and three-dimensional modeling.

RECENT FINDINGS

Several studies have demonstrated the utility of dynamic imaging modalities. Specifically, radiographic patellar tracking correlates with symptomatic instability, and quadriceps activation and weightbearing alter patellar kinematics. Further advancements include the study of three-dimensional models. Automation of commonly utilized measurements such as tibial tubercle-trochlear groove (TT-TG) distance has the potential to resolve issues with inter-rater reliability and fluctuation with knee flexion or tibial rotation. Future directions include development of robust computational models (e.g., finite element analysis) capable of incorporating patient-specific data for surgical planning purposes. While several studies have utilized novel dynamic imaging and modeling techniques to enhance our understanding of patellofemoral joint mechanics, these methods have yet to find a definitive clinical utility. Further investigation is required to develop practical implementation into clinical workflow.