How accurate and reproducible are the identification of cruciate and collateral ligament insertions using MRI?

The use of virtual reality to assess the bony landmarks at the knee joint - The role of imaging modality and the assessor's experience

BACKGROUND

At present, extended reality technologies such as virtual reality (VR) have gained popularity in orthopedic surgery. The first aim of this study was to assess the precision of VR and other imaging modalities - computed tomography (CT), magnetic resonance imaging (MRI) - to localize bony landmarks near the knee joint. Secondly, the impact of the educational level of the assessor - medical master students, orthopedic residents, and orthopedic surgeons - on the precision with which landmarks near the knee joint could be localized was analyzed.

METHODS

We included a total of 77 participants: 62 medical master students, 10 orthopedic residents, and 5 orthopedic surgeons to analyze three cadaver legs. Every participant localized a series of sixteen bony landmarks on six different imaging modalities (CT, MRI, 3D-CT, 3D-MRI, VR-CT, VR-MRI).

RESULTS

Concerning the imaging modality, the inter- and intra-observer variability were lowest for 3D and VR, higher for MRI (respectively 7.6 mm and 6.9 mm), and highest for CT (respectively 9 mm and 8.7 m).Concerning the educational level of the assessor, inter- and intra-observer variability in VR were lowest for surgeons, (respectively 3.2 mm and 3.6 mm), higher for residents (respectively 5.9 mm and 6.5 mm) and medical students (respectively 5.9 mm and 5.8 mm).

CONCLUSIONS

VR can be considered a reliable imaging technique. Localization of landmarks tends to be more precise in VR and on 3D than on conventional CT and MRI images. Furthermore, orthopedic surgeons localize landmarks more precisely than orthopedic residents and medical students in VR.

How reproducible are clinical measurements in robotic knee surgery?

PURPOSE

Robotic-assisted surgery has been recently introduced to improve biomechanical restoration, and thus better clinical and functional outcomes, after knee joint arthroplasty operations. Robotic-assisted uni-compartmental knee arthroplasty (UKA) aims indeed to improve surgical bone resection and alignment accuracy, optimized component positioning and knee balancing, relying on a series of calibration measurements performed during the surgery. These advantages focus therefore on improving the reproducibility of UKA surgeries, reducing (if not eliminating) eventual differences among high- and low-volume surgeons. The purpose of this study is to investigate and quantify the reproducibility of in-vivo measurements performed with a robotic system: the intra- and inter-observer variability of a series of measurements was therefore analyzed and compared among differently experienced operators.

METHODS

Five patients were analyzed and underwent robotic-assisted UKA using a semi-active robotic system. Three different observers with different experience levels were involved to independently perform the measurements of two parameters of the preoperative knee (Hip-Knee-Ankle angle [HKAa], Internal-External Rotation) at different degrees of knee flexion. Inter-observer and intra-observer comparisons were performed.

RESULTS

The average variability in the measurements obtained from the intra-observer and inter-observer comparisons were always < 0.68° for HKAa and < 2.59° for internal-external rotation, and the ICCs showed excellent agreement (> 0.75) for most cases and good agreement (> 0.60) in the remaining ones.

CONCLUSION

This study demonstrated high reproducibility of the measurements obtainable in clinical environment with the robotic system. The inter-observer results furthermore showed that the level of confidence with the robotic system is not significantly influencing the measurement.

Experimental and clinical analysis of the use of asymmetric vs symmetric polyethylene inserts in a mobile bearing total knee arthroplasty

Purpose

This study compared the effects of symmetric and asymmetric designs for mobile bearing polyethylene insert for total knee arthroplasty (TKA), both clinically and biomechanically through experimental cadaver tests.

Methods

303 patients implanted with a mobile bearing TKA were retrospectively analyzed up to 2-year follow-up with relative scores. The same femoral and tibial components were used for all the patients; 151 patients received a Symmetric Design (SD) insert and 152 an Asymmetric Design (AD). A biomechanical experimental test was performed to improve the comprehension of the clinical results, analyzing passive squat on 5 cadaveric knee specimens: internal-external rotations of femur and tibial insert respect to the tibia tray were analyzed in native and implanted configurations (with both symmetrical and asymmetrical inserts for each specimen).

Results

After surgery, patients' average flexion improved from 105° (with preoperative extension deficit of 5°), to 115° (SD-group) and 120° (AD-group) at the 2-year follow-up. There was no postoperative extension deficit. AD-group presented better ability to perform certain routines and wasn't affected by any pain, while antero-lateral pain was reported in some SD-group patients. The experimental tests returned no statistically relevant difference in tibio-femoral flexion-extension and internal-external rotations among all the three configurations tested; a statistically significant difference is found for insert-tray internal-external rotations between SD and AD configurations; in details, the AD insert showed insert-tray angles comparable to the ones found for femoral component-tibial tray, while the SD insert returned lower angular values.

Conclusion

Clinically and biomechanically, an asymmetric mobile bearing insert could represent a valid alternative to symmetric mobile bearing insert.

Level of evidence

III, Case-control study Retrospective comparative study.

Change in knee biomechanics during squat and walking induced by a modification in TKA size

The purpose of this study is to analyze the effects of TKA under-dimensioning during daily activities. A regular ("control") size and an undersized design of the same fixed bearing asymmetric PS prosthesis were analyzed during walking and squat using finite element analysis. The two models showed similar internal-external rotations and antero-posterior displacements during both activities. Slightly higher displacements, wider contact areas and lower contact pressure were found in the control size. Post-cam engagement angles were similar on both sizes. Changes in TKA size slightly affected knee kinematics and kinetics, with post-cam related differences leading to minor changes in kinetic patterns.

Development and validation of an in-silico virtual testing rig for analyzing total knee arthroplasty performance during passive deep flexion: A feasibility study

The use of in-silico finite element (FE) models has become more common in orthopedic applications and in the design of biomedical devices, since they can provide results comparable to in vitro experiments while maintaining lower cost. The main downside of this kind of analysis is the high computing time, as it can reach hours or even days to complete; this limitation makes it then not suitable for time-sensitive applications, such as probabilistic analyses or helping clinicians in surgical pre-planning or intra-operative setting. In-silico multibody (MB) simulations, on the other hand, are significantly faster than FE simulations (considering each component of the model as a rigid body); although deformability of each model component is a necessary feature in some applications (e.g. simulation of implant-bone micromotions), several outputs of interest in orthopedic applications, such as implant kinematics and contact forces, do not require a fully deformable model. Therefore, this feasibility study aimed to develop a MB model of a human knee joint implanted with a Total Knee Arthroplasty; a 10 second flexion movement up to 105° was then simulated and the results compared with validated FE models results (under similar boundary conditions) from literature, to perform a preliminary validation in terms of kinematic and kinetic results between the two methods. The agreement and relatively low computing time obtaining with this approach represent a promising starting point for subsequent studies and applications of such techniques in the clinical field.

High congruency MB insert design: stabilizing knee joint even with PCL deficiency

PURPOSE

PCL management and choice of insert design and mobility in total knee arthroplasty are still debated in the literature. Consequently, the purpose of this study was to analyze the biomechanics of a fixed and a mobile bearing total knee arthroplasty with conventional and ultra-congruent insert during walking and squat activities, using finite element analysis, and to check the performance in a knee with healthy and deficient PCL.

METHODS

The study was based on an already validated and published knee model. Fixed bearing and mobile bearing cruciate-retain designs were selected for this study. Implant kinematics and kinetics were calculated, following previously experimental tests, during a walking cycle and a loaded squat in a knee with intact and with deficient PCL.

RESULTS

Mobile bearing design, due to its higher congruency, was able to complete the task in intact and deficient PCL conditions, with similar internal-external femoral rotation and with a slight higher anterior translation of the one of the intact knees. Such outcomes were also in agreement with the results of different experimental studies of native knee specimens under similar boundary conditions. Contrariwise, fixed bearing design was able to accomplish the task only in healthy PCL conditions.

CONCLUSION

Results demonstrated how the high congruency of the mobile bearing design is able to guarantee proper knee stability and kinematics even when the PCL is deficient. Instead, the fixed bearing insert, with lower congruency, is not able, in the absence of the PCL, to stabilize the joint inducing irregular kinematic pattern and component dislocation. Surgeons will have to consider these findings to guarantee the best outcome for the patient and the related change in stability in case of PCL deficiency.

Accuracy of manual and automatic placement of an anatomical coordinate system for the full or partial radius in 3D space

Accurate placement of a coordinate system on the radius is important to quantitatively report 3D surgical planning parameters or joint kinematics using 4D imaging techniques. In clinical practice, the scanned length of the radial shaft varies among scanning protocols and scientific studies. The error in positioning a radial coordinate system using a partially scanned radius is unknown. This study investigates whether the imaged length of the radius significantly affects the positioning of the coordinate system. For different lengths of the radius, the error of positioning a coordinate system was determined when placed automatically or manually. A total of 85 healthy radii were systematically shortened until 10% of the distal radius remained. Coordinate systems were placed automatically and manually at each shortening step. A linear mixed model was used to associate the positioning error with the length of the radial shaft. The accuracy and precision of radial coordinate system placement were compared between automatic and manual placement. For automatic placement of the radial coordinate system, an increasing positioning error was associated with an increased shortening of the radius (P = < 0.001). Automatic placement is superior to manual placement; however, if less than 20% of the radial shaft length remains, manual placement is more accurate.

Development and validation of a robust patellar reference coordinate system for biomechanical and clinical studies

BACKGROUND

This study aimed to develop and validate a reference coordinate system for the human patella, based on the registration of bony landmarks on a computed tomography (CT) scan.

METHODS

Thirty-three native cadaveric specimens were scanned, and an observer marked a set of seven anatomical landmarks on each of them. Such markers were used to define the reference coordinate system. In order to validate its robustness, statistical distribution of the point registration was then studied. Afterwards, three different observers marked the anatomical landmarks on a sub-sample of six specimens and the intra-observer and inter-observer variability of the point registration was performed.

RESULTS

Results of this study showed the highest values to be 1.46 mm (intra) and 4.08 mm (inter), both observed for the patellar ridge top. The intra-class correlation coefficient (ICC) for inter-observer variability ranked higher than 0.8 for all the landmarks used for the identification of the reference frame, and ranged from 0.4-0.9 for other landmarks.

CONCLUSIONS

This study demonstrates low intra-observer and inter-observer variability in the CT registration of landmarks that define and validate a robust coordinate system of the patella that could be used to perform accurate biomechanical and clinical studies.

Asymmetric polyethylene inserts promote favorable kinematics and better clinical outcome compared to symmetric inserts in a mobile bearing total knee arthroplasty

PURPOSE

This study aims at comparing the effects of symmetric and asymmetric designs for the polyethylene insert currently available and also for mobile bearing total knee arthroplasty (TKA). The investigation was performed both clinically and biomechanically through finite element analysis.

METHODS

303 patients, with a mobile bearing TKA, were analyzed retrospectively. All patients received the same femoral and tibial components; for the insert, 151 patients received a symmetric design (SD) and 152 an asymmetric design (AD). Additionally, a 3D finite element model of a lower leg was developed, resurfaced with the same TKAs and analysed during gait and squat activities. TKA kinematics, and bone-stresses were investigated for the two insert solutions.

RESULTS

After surgery, patients' average flexion improved from 105°, with 5° of preoperative extension deficit, to 120° (AD-group) and 115° (SD-group) at the latest follow-up. There was no postoperative extension deficit. No pain affected the AD-group, while an antero-lateral pain was reported in some patients of the SD-group. Patients of the AD-group presented a better ability to perform certain physical routines. Biomechanically, the SD induced higher tibial-bone stresses than the AD. Both designs replicated similar kinematics, comparable to literature. However, SD rotates more on the tray, reducing the motion between femoral and polyethylene components, while AD permits greater insert rotation.

CONCLUSION

The biomechanical analysis justifies the clinical findings. TKA kinematics is similar for the two designs, although the asymmetric solution shows less bone stress, thus resulting as more suitable to be cemented, avoiding lift-off issues, inducing less pain. Clinically, and biomechanically, an asymmetric mobile bearing insert could be a valid alternative to symmetric mobile bearing insert.

LEVEL OF EVIDENCE

Case-control study retrospective comparative study, III.

Sensitivity analysis of the material properties of different soft-tissues: implications for a subject-specific knee arthroplasty

Introduction

While developing a subject-specific knee model, different kinds of data-inputs are required. If information about geometries can be definitely obtained from images, more effort is necessary for the in vivo properties. Consequently, such information are recruited from the literature as common habit. However, the effects of the combined sources still need to be evaluated.

Methods

This work aims at developing an intact native subject-specific knee model for performing a sensitivity analysis on soft-tissues. The impacts on the biomechanical outputs were analysed during a daily activity for which articular knee kinetics and kinematics were compared among the different configurations. Prior to the sensitivity analysis, experimental and literature data were checked for the model reliability.

Results

Average values of mixed sources allowed the agreement with experimental data for personalized outputs. From the sensitivity analysis, knee kinematics did not significantly change in the selected ranges of properties for the soft-tissues (in rotation less than 0.5°), while contact stresses were greatly affected, especially for the articular cartilage (with differences in the results more than 100%).

Conclusion

In conclusion, during the development of a personalized knee model, the selection of the correct material properties is fundamental because wrong values could highly affect the numerical results.

Level of evidence

III a.