Current treatment for end-stage osteoarthritis is total knee replacement. Given that the number of total knee replacement surgeries is expected to approach 3.48 million by 2030, understanding long-term failure is important. One of the preclinical tests for total knee replacements is carried out using mechanical wear testing under generic walking conditions. Used for this purpose is the International Standards Organization's generic walking profile. Recently this standard was updated by reversing the direction of anterior/posterior translation and internal/external rotation. The effects of this change have not been investigated, and therefore, it is unknown if comparisons between wear tests utilizing the old and new version of the standard are valid. In this study, we used a finite element model along with a frictional energy-based wear model to compare the kinematic inputs, contact conditions, and wear from the older and newer versions of the ISO standard. Simulator-tested components were used to validate the computational model. We found that there were no visible similarities in the contact conditions between the old and new versions of the standard. The new version of the standard had a lower wear rate but covered a larger portion of the articular surface. Locations of wear also varied considerably. The results of the study suggest that major differences between the old and new standard exist, and therefore, historical wear results should be compared with caution to newly obtained results.
Polyethylene wear particles have been linked to osteolysis after total ankle arthroplasty. There is no consensus on the importance of highly cross-linked polyethylene in total ankle arthroplasty with regard to implant wear. This is the first nonindustry study to compare the polyethylene wear rate, particle size, and particle shape of fixed-bearing total ankle arthroplasty conventional polyethylene versus highly cross-linked polyethylene. The lower wear rate and different particle size/morphology of highly cross-linked polyethylene could be beneficial in vivo to decrease osteolysis.
Total knee arthroplasty is on the rise worldwide. Despite its success, revision surgeries are also increasing. According to the American Joint Replacement Registry 2020, 3.3% of revision surgeries are due to wear, and 24.2% are due to mechanical loosening. The combination of shear stresses and wear particles occurring at the bone/implant interface can lead to local osteolysis. Although the shear stresses are partially driven by joint friction, relatively little is known about the evolution of the coefficient of friction (CoF) during a gait cycle in total knee replacement. Here we describe the CoF during a gait cycle and investigate its association with kinematics (slide–roll-ratio), applied load, and relative velocity. The artificial knee was simulated by cobalt–chromium condyle on a flat ultra-high-molecular-weight polyethylene (UHMWPE) tibial plateau, lubricated by either water or proteinaceous solution. We found that the CoF is not a constant but fluctuates between the values close to 0 and 0.15. Cross-correlation suggested that this is primarily an effect of the slide–roll ratio and the contact pressure. There was no difference in the CoF between water and proteinaceous solution. Knowledge about the CoF behavior during a gait cycle will help to increase the accuracy of future computational models of total knee replacement.
Bone microarchitectural parameters significantly contribute to implant fixation strength but the role of bone matrix composition is not well understood. To determine the relative contribution of microarchitecture and bone matrix composition to implant fixation strength, we placed titanium implants in 12‐week‐old intact Sprague–Dawley rats, ovariectomized‐Sprague–Dawley rats, and Zucker diabetic fatty rats. We assessed bone microarchitecture by microcomputed tomography, bone matrix composition by Raman spectroscopy, and implant fixation strength at 2, 6, and 10 weeks postimplantation. A stepwise linear regression model accounted for 83.3% of the variance in implant fixation strength with osteointegration volume/total volume (50.4%), peri‐implant trabecular bone volume fraction (14.2%), cortical thickness (9.3%), peri‐implant trabecular crystallinity (6.7%), and cortical area (2.8%) as the independent variables. Group comparisons indicated that osseointegration volume/total volume was significantly reduced in the ovariectomy group at Week 2 (~28%) and Week 10 (~21%) as well as in the diabetic group at Week 10 (~34%) as compared with the age matched Sprague–Dawley group. The crystallinity of the trabecular bone was significantly elevated in the ovariectomy group at Week 2 (~4%) but decreased in the diabetic group at Week 10 (~3%) with respect to the Sprague–Dawley group. Our study is the first to show that bone microarchitecture explains most of the variance in implant fixation strength, but that matrix composition is also a contributing factor. Therefore, treatment strategies aimed at improving bone‐implant contact and peri‐implant bone volume without compromising matrix quality should be prioritized.
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