Microtextured CoCrMo alloy for use in metal-on-polyethylene prosthetic joint bearings: multi-directional wear and corrosion measurements

Cartilage-inspired surface textures for improved tribological performance of orthopedic implants

Joint replacements have become one of the most common orthopedic procedures due to the significant demands of retaining functional mobility. While these procedures are of great value to patients, there are some limitations. Durability is the most important limitation associated with joint replacement that needs to be addressed due to the increasing number of younger patients. Titanium is a commonly used implant material which has high biocompatibility, high strength-to-density ratio, and high corrosion resistance. However, current titanium implants have poor wear resistance which shortens their lifespan. In this study, microscale dimples with four different dimple shapes (circular, triangular, square, and star) of similar sizes to the pores found in natural articular cartilage were fabricated on titanium disks to improve implant lubrication and reduce wear. Biotribology tests were performed on dimpled and non-dimpled titanium disks in a condition similar to that inside of a patient's body. It was shown that dimpling the titanium disks optimized the lubricant film formation and decreased the wear rate significantly while also reducing the coefficient of friction (COF). The star-shaped dimples had the lowest COF and almost no detectable wear after 8 h of testing. To investigate whether dimpling increased bacterial colonization due to increased surface area, and to determine whether any increase could be limited by coating with antibacterial materials, bacterial colonization with Staphylococcus aureus was tested with non-dimpled and star-shaped dimpled titanium disks with and without coating with polydopamine (PDA), silver (Ag) nanoparticles (NPs), and PDA + Ag NPs. It was found that dimpling did not increase bacterial colonization, and that coating with PDA, Ag NPs, or PDA + Ag NPs did not decrease bacterial colonization. Nevertheless, we conclude that star-shaped dimpled titanium surfaces have potential utility as more durable orthopedic implants.

Evaluation of artificial intelligence models for osteoarthritis of the knee using deep learning algorithms for orthopedic radiographs

BACKGROUND

Deep learning, a form of artificial intelligence, has shown promising results for interpreting radiographs. In order to develop this niche machine learning (ML) program of interpreting orthopedic radiographs with accuracy, a project named deep learning algorithm for orthopedic radiographs was conceived. In the first phase, the diagnosis of knee osteoarthritis (KOA) as per the standard Kellgren-Lawrence (KL) scale in medical images was conducted using the deep learning algorithm for orthopedic radiographs.

AIM

To compare efficacy and accuracy of eight different transfer learning deep learning models for detecting the grade of KOA from a radiograph and identify the most appropriate ML-based model for the detecting grade of KOA.

METHODS

The study was performed on 2068 radiograph exams conducted at the Department of Orthopedic Surgery, Sir HN Reliance Hospital and Research Centre (Mumbai, India) during 2019-2021. Three orthopedic surgeons reviewed these independently, graded them for the severity of KOA as per the KL scale and settled disagreement through a consensus session. Eight models, namely ResNet50, VGG-16, InceptionV3, MobilnetV2, EfficientnetB7, DenseNet201, Xception and NasNetMobile, were used to evaluate the efficacy of ML in accurately classifying radiographs for KOA as per the KL scale. Out of the 2068 images, 70% were used initially to train the model, 10% were used subsequently to test the model, and 20% were used finally to determine the accuracy of and validate each model. The idea behind transfer learning for KOA grade image classification is that if the existing models are already trained on a large and general dataset, these models will effectively serve as generic models to fulfill the study’s objectives. Finally, in order to benchmark the efficacy, the results of the models were also compared to a first-year orthopedic trainee who independently classified these models according to the KL scale.

RESULTS

Our network yielded an overall high accuracy for detecting KOA, ranging from 54% to 93%. The most successful of these was the DenseNet model, with accuracy up to 93%; interestingly, it even outperformed the human first-year trainee who had an accuracy of 74%.

CONCLUSION

The study paves the way for extrapolating the learning using ML to develop an automated KOA classification tool and enable healthcare professionals with better decision-making.

Influence of Cross-Shear and Contact Pressure on Wear Mechanisms of PEEK and CFR-PEEK in Total Hip Joint Replacements

With the increasing market demand for artificial hip joints, total hip joint replacement has gradually become an effective means of treating a series of hip joint diseases. In order to improve the service life of artificial hip joints, some new artificial hip joint materials, including polyetheretherketone (PEEK) and carbon fiber reinforced polyetheretherketone (CFR-PEEK), have been developed. In this paper, pin-on-plate wear tests under different cross-shear ratios and contact pressures were carried out to study the wear mechanism and worn surface topography of PEEK and CFR-PEEK. The experimental results showed that the wear of PEEK was associated with cross-shear, while CFR-PEEK was not. When the cross-shear ratio was 0.039 and contact pressure was 3.18 MPa, PEEK had poor wear resistance and its wear factor was about eight times that of ultra-high molecular weight polyethylene (UHMWPE). The wear resistance of CFR-PEEK had a significant advantage, since its wear factor was about 30% of that of PEEK. The wear factors of PEEK and CFR-PEEK increased as the contact pressure increased. The arithmetic average of the height amplitude of the surface, Sa, also increased gradually according to the topography of the worn surface. The wear mechanisms of PEEK and CFR-PEEK were scratching, plough cutting, and abrasion Since CFR-PEEK had good wear resistance and insensitivity to cross-shear motion, it is suitable for making artificial hip joints under low contact pressure condition.

Surface Texturing of Prosthetic Hip Implant Bearing Surfaces: A Review

More than 300,000 total hip replacement surgeries are performed in the United States each year to treat degenerative joint diseases that cause pain and disability. The statistical survivorship of these implants declines significantly after 15-25 years of use because wear debris causes inflammation, osteolysis, and mechanical instability of the implant. This limited longevity has unacceptable consequences, such as revision surgery to replace a worn implant, or surgery postponement, which leaves the patient in pain. Innovations such as highly cross-linked polyethylene and new materials and coatings for the femoral head have reduced wear significantly, but longevity remains an imminent problem. Another method to reduce wear is to add a patterned microtexture composed of micro-sized texture features to the smooth bearing surfaces. We critically review the literature on textured orthopedic biomaterial surfaces in the context of prosthetic hip implants. We discuss the different functions of texture features by highlighting experimental and simulated results documented by research groups active in this area. We also discuss and compare different manufacturing techniques to create texture features on orthopedic biomaterial surfaces and emphasize the key difficulties that must be overcome to produce textured prosthetic hip implants.

The Effect of Texture Floor Profile on the Lubricant Film Thickness in a Textured Hard-On-Soft Bearing With Relevance to Prosthetic Hip Implants

Polyethylene wear debris limits the longevity of prosthetic hip implants. We design a pattern of axisymmetric texture features to increase hydrodynamic pressure and lubricant film thickness and, thus, reduce solid-on-solid contact, friction, and wear in hard-on-soft prosthetic hip implant bearings. Specifically, we study the effect of the texture floor profile on the lubricant film thickness using a soft elastohydrodynamic lubrication model. We compute the optimum texture parameters that maximize the lubricant film thickness for different texture floor profiles, as a function of bearing operating conditions. Flat texture floor profiles create thicker lubricant films than sloped or curved texture floor profiles for their respective optimum texture design parameters. We find that the texture feature volume is the most important parameter in terms of maximizing the lubricant film thickness, because a linear relationship exists between the texture feature volume with optimum texture parameters and the corresponding optimum lubricant film thickness, independent of the texture floor profile.

Maximizing the Lubricant Film Thickness Between a Rigid Microtextured and a Smooth Deformable Surface in Relative Motion, Using a Soft Elasto-Hydrodynamic Lubrication Model

We design a pattern of microtexture features to increase hydrodynamic pressure and lubricant film thickness in a hard-on-soft bearing. We use a soft elastohydrodynamic lubrication model to evaluate the effect of microtexture design parameters and bearing operating conditions on the resulting lubricant film thickness and find that the maximum lubricant film thickness occurs with a texture density between 10% and 40% and texture aspect ratio between 1% and 14%, depending on the bearing load and operating conditions. We show that these results are similar to those of hydrodynamic textured bearing problems because the lubricant film thickness is almost independent of the stiffness of the bearing surfaces in full-film lubrication.

Ring-Shaped Surface Microstructures for Improved Lubrication Performance of Joint Prostheses

The microstructuring of surfaces is a highly researched field that is aimed at enhancing the tribological behavior of sliding surfaces such as artificial joints, which are subject to wear. Lubrication of the joint interface plays a key role in the wear process, although the mechanisms of lubrication are quite complex. In order to improve the lubrication, the surfaces of the articulating components can be modified by pulsed femtosecond-laser microstructuring. Through microstructuring, the apparent dynamic viscosity of the synovial fluid between the artificial joint can be increased due to its non-Newtonian properties. This may lead to better hydrodynamic lubrication and, therefore, reduced particle abrasion. Femtosecond laser-induced microstructures were investigated in a modified rheometer setup featuring a reduced gap size in order to reproduce and measure the interface between fluid and implant surface more accurately. As a test fluid, a synovial fluid substitute was used. The study has shown that an increase in the viscosity of the synovial fluid substitute can be achieved by microstructuring. Compared to a smooth implant surface, the apparent viscosity of the synovial fluid substitute increased by over 30% when ring-shaped microstructures of 100 µm diameter with an aspect ratio of 0.66 were implemented.

Polydopamine-Assisted Immobilization of Chitosan Brushes on a Textured CoCrMo Alloy to Improve its Tribology and Biocompatibility

Due to their bioinert and reliable tribological performance, cobalt chromium molybdenum (CoCrMo) alloys have been widely used for articular joint implant applications. However, friction and wear issues are still the main reasons for the failure of implants. As a result, the improvement of the tribological properties and biocompatibility of these alloys is still needed. Thus, surface modification is of great interest for implant manufacturers and for clinical applications. In this study, a strategy combining laser surface texturing and chitosan grafting (mussel inspired) was used to improve the tribological and biocompatible behaviors of CoCrMo. The microstructure and chemical composition were investigated by atomic force microscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The tribological properties were discussed to determine their synergistic effects. To evaluate their biocompatibility, osteoblast cells were cocultured with the modified surface. The results show that there is a distinct synergistic effect between laser surface texturing and polymer brushes for improving tribological behaviors and biocompatibility. The prepared chitosan brushes on a textured surface are a strong mechanism for reducing friction force. The dimples took part in the hydrodynamic lubrication and acted as the container for replenishing the consumed lubricants. These brushes also promote the formation of a local lubricating film. The wear resistance of the chitosan brushes was immensely improved. Further, the worn process was observed, and the mechanism of destruction was demonstrated. Co-culturing with osteoblast cells showed that the texture and grafting have potential applications in enhancing the differentiation and orientation of osteoblast cells.

Predicting the polyethylene wear rate in pin-on-disc experiments in the context of prosthetic hip implants: deriving a data-driven model using machine learning methods

Pin-on-disc (PoD) experiments are widely used to quantify and rank wear of different material couples for prosthetic hip implant bearings. However, polyethylene wear results obtained from different PoD experiments are sometimes difficult to compare, which potentially leaves information inaccessible. We use machine learning methods to implement several data-driven models, and subsequently validate them by quantifying the prediction error with respect to published experimental data. A data-driven model can supplement results from PoD wear experiments, and enables predicting polyethylene wear of new PoD experiments based on its operating parameters. It also reveals the relative contribution of individual PoD operating parameters to the resulting polyethylene wear, thus informing design of experiments, and potentially reducing the need for time consuming PoD wear measurements.

Friction between a polyethylene pin and a microtextured CoCrMo disc, and its correlation to polyethylene wear, as a function of sliding velocity and contact pressure, in the context of metal-on-polyethylene prosthetic hip implants

The longevity of metal-on-polyethylene prosthetic hip implant bearings, in which a polished CoCrMo femoral head articulates with a polyethylene liner, is limited by mechanical instability or inflammation resulting from osteolysis caused by polyethylene wear debris. We use pin-on-disc experiments to measure friction and wear of a polyethylene pin that articulates with different microtextured CoCrMo surfaces, covering a wide range of operating conditions including sliding velocity and contact pressure. We determine how the lubrication regime changes as a function of operating conditions, and show that the microtexture accelerates the transition from boundary to elastohydrodynamic lubrication. Additionally, we illustrate that the microtexture could enable tailoring the hip implant to the specific patient needs based on activity level, gender, and age.