Nanoscale Surface Refinement of CoCrMo Alloy for Artificial Knee Joints via Chemical Mechanical Polishing.

In this study, we address the challenge of surface roughness in CoCrMo alloys, typically used in artificial knee joints, which can initiate a cascade of biological responses causing inflammation, osteolysis, joint instability, and increased susceptibility to infection. We propose the application of a chemical mechanical polishing (CMP) technique, using an ecologically responsible slurry composed of 4 wt% SiO2, 0.3 wt% H2O2, 1.0 wt% glycine, and 0.05 wt% benzotriazole. Our innovative approach demonstrated significant improvements, achieving a material removal rate of 30.9 nm/min and reducing the arithmetic mean roughness from 20.76 nm to 0.25 nm, thereby enhancing the nanoscale surface quality of the artificial knee joint alloy. The smoother surface is attributed to a decrease in corrosion potential to 0.18 V and a reduction in corrosion current density from 9.55 µA/cm2 to 4.49 µA/cm2 with the addition of BTA, evidenced by electrochemical tests. Furthermore, the preservation of the phase structure of the CoCrMo alloy, as confirmed by XRD analysis and elemental mapping, ensures the structural integrity of the treated surfaces. These outcomes and our simulation results demonstrate the effectiveness of our CMP method in engineering surface treatments for artificial knee joints to optimize friction behavior and potentially extend their lifespans.

Rotation-hinged knee prosthesis for the treatment of Charcot arthropathy: a case report and literature review.

Charcot arthropathy is a type of destructive osteoarthropathy characterized by neurotrophic and sensory disorders. The condition is relatively rare, with an insidious onset, and it is easily misdiagnosed. Total knee arthroplasty (TKA) can cause excessive joint wear, continuous inflammatory stimulation of the prosthesis, postoperative residual cavity, prosthesis loosening and subsidence, peripheral fracture, infection, and other complications. Furthermore, these complications are more likely to occur in patients with Charcot arthropathy because of disease-specific pathological characteristics, when TKA is performed. Therefore, Charcot arthropathy was once a contraindication to TKA. Recently, with the optimization of joint prostheses and the maturity of surgical techniques, more studies have reported successful cases of TKA in patients with Charcot arthropathy. We report a case of Charcot arthropathy in our hospital, and describe the patient's medical history, clinical symptoms, signs, imaging findings, diagnosis, and the entire TKA process, to explore the TKA strategy and prosthesis selection in a patient with Charcot arthropathy.

Effects of knee simulator control method and radiation dose on UHMWPE wear rate, and relationship between wear rate and clinical revision rate in National Joint Registry.

The wear rate of five types of cruciate-retaining artificial knee joint ultrahigh-molecular-weight polyethylene (UHMWPE) inserts was examined using two custom-made knee joint simulators satisfying ISO 14243-1 (load control) and ISO 14243-3 (displacement control). The wear rate of knee joints composed of a UHMWPE insert and a Co-Cr-Mo alloy or oxidized zirconium femoral component linearly increased with increasing number of wear cycles, and the volumetric wear rate per million cycles was approximately 6-18 mm3/Mc. The wear rate was the lowest in the highly crosslinked knee joint irradiated at 90 kGy (Scorpio) among the five UHMWPE inserts. The extent of oxidation in UHMWPE after a knee simulator test of up to 5 × 106 cycles was small. The load-controlled wear rates measured in this work were close to the displacement-controlled wear rates reported in the literature. The effect of the control method on the wear rate was small for Nexgen and Scorpio knee joints. However, it was larger for the PFC Sigma knee joint having a high curvature of the surface. The wear rate of various knee joints made of highly crosslinked UHMWPE (XLPE) markedly decreased when they were subjected to a radiation dose of 40 kGy or more. The 10-year cumulative percentage revision rate since the primary operation slightly decreased with decreasing volumetric knee simulator wear rate for conventional UHMWPE (CPE) and XLPE knee joint inserts. The XLPE knee joint was shown to exhibit reduced in vivo wear and lower rates of revision for total knee replacement. On the other hand, Nexgen and PFC Sigma (both CPE) knee joints showed the lowest revision rate in the AOA and NJR national joint replacement registries. The volumetric wear rates of 3 mm3/Mc for XLPE and 15 mm3/Mc for CPE knee joint inserts are recommended as a goal for the development of new knee joints.

Torsional friction behavior of the contact interface between the materials of an artificial knee joint replacement.

The torsional friction behavior of the materials (CoCrMo alloy and ultra-high-molecular-weight polyethylene (UHMWPE)) that are used in artificial knee joint replacement (AKJR) were investigated under dynamic loading. The torsional friction torque, wear loss and scars and stress distribution were analyzed and compared. The results show the following: (1) the friction torque declines rapidly at the beginning of the experiments, and meanwhile, the maximum normal load and the torsional angle amplitude show very little effect on the steady value; (2) the wear loss decreases with the increased torsional angle amplitude but increases with the increased maximum normal load; additionally, as the cycle times increase, the wear rate decreases, and the wear is minimal; (3) unloading and secondary loading significantly reduce the friction and wear of the materials, and thus, patients should rest after prolonged exercise to reduce wear; (4) the margins of UHMWPE and CoCrMo are worn, and the wear mechanism is abrasive wear; (5) around the center of the UHMWPE, the surface is peeled off, and the wear mechanism is fatigue wear; and (6) in terms of the compressive stress and shear stress, the calculated results from a finite element model match the experimental results well.

Fractal Characterization and Classification Characteristics of the Artificial Joint Wear Particles / 医用生物力学

Objective To study the morphology and fractal characterization of UHMWPE wear particles by simulation experiment on knee joint, analyze the classification characteristics of wear particles and discuss the correlation between fractal dimension and wear state. Methods The knee joint simulator was used to realize the knee joint wear motion. The forged CoCrMo alloy and UHMWPE were selected as artificial joint prosthesis materials. The wear particle extraction was based on ISO 17853. The automatic extraction and fractal identification system of wear particles were used to investigate fractal characteristics of wear particles. Three kinds of models were established to classify and recognize wear particles, by using the meshing method, cluster analysis and genetic simulated annealing algorithm, respectively. Results The fractal characteristics of UHMWPE single wear particles was very obvious. The fractal dimension calculated by radar fractal method decreased, during the transition from the larger size of strip debris to the smaller size of roundness debris, and the fractal dimension D of spherical debris was close to zero. The weighted sum of squared error values of fractal dimension for wear particle population classification was the smallest by the model of genetic simulated annealing algorithm, and the clustering feature was very obvious. When the wear cycles were low, the large fractal dimension of strip, needle and fibrous abrasive debris with larger fractal dimension had the largest proportion, and the main abrasion modes were the ploughing and spalling wears. With the extension of wear period, the proportion of wear particles with large fractal dimension decreased, and the proportion of flaky, blocky and near-spherical wear particles with low fractal dimension increased clearly. The wear mechanism changed to the fatigue and adhesive wear, and the wear state transited to the composite wear period. During the stable wear period, the proportion of all kinds of abrasive grains changed little. Due to the increase in the number of small particles, the fractal dimension decreased in stable wear state. Conclusions Based on the improved radar graph method, the fractal dimension of wear particles with different profiles could be obtained by automatic extraction and fractal identification system of wear particles. The research findings can be used in shape extraction, fractal dimension calculation and parameter statistics, as well as providing a new digital analysis tool for identification and diagnosis for wear particles of artificial prosthesis.

Functional in situ assessment of human articular cartilage using MRI: a whole-knee joint loading device.

The response to loading of human articular cartilage as assessed by magnetic resonance imaging (MRI) remains to be defined in relation to histology and biomechanics. Therefore, an MRI-compatible whole-knee joint loading device for the functional in situ assessment of cartilage was developed and validated in this study. A formalin-fixed human knee was scanned by computed tomography in its native configuration and digitally processed to create femoral and tibial bone models. The bone models were covered by artificial femoral and tibial articular cartilage layers in their native configuration using cartilage-mimicking polyvinyl siloxane. A standardized defect of 8 mm diameter was created within the artificial cartilage layer at the central medial femoral condyle, into which native cartilage samples of similar dimensions were placed. After describing its design and specifications, the comprehensive validation of the device was performed using a hydraulic force gauge and digital electronic pressure-sensitive sensors. Displacement-controlled quasi-static uniaxial loading to 2.5 mm [Formula: see text] and 5.0 mm [Formula: see text] of the mobile tibia versus the immobile femur resulted in forces of [Formula: see text] N [Formula: see text] and [Formula: see text] N [Formula: see text] (on the entire joint) and local pressures of [Formula: see text] MPa [Formula: see text] and [Formula: see text] MPa [Formula: see text] (at the site of the cartilage sample). Upon confirming the MRI compatibility of the set-up, the response to loading of macroscopically intact human articular cartilage samples ([Formula: see text]) was assessed on a clinical 3.0-T MR imaging system using clinical standard proton-density turbo-spin echo sequences and T2-weighted multi-spin echo sequences. Serial imaging was performed at the unloaded state [Formula: see text] and at consecutive loading positions (i.e. at [Formula: see text] and [Formula: see text]. Biomechanical unconfined compression testing (Young's modulus) and histological assessment (Mankin score) served as the standards of reference. All samples were histologically intact (Mankin score, [Formula: see text]) and biomechanically reasonably homogeneous (Young's modulus, [Formula: see text] MPa). They could be visualized in their entirety by MRI and significant decreases in sample height [[Formula: see text]: [Formula: see text] mm; [Formula: see text]: [Formula: see text] mm; [Formula: see text]: [Formula: see text] mm; [Formula: see text] (repeated-measures ANOVA)] as well as pronounced T2 signal decay indicative of tissue pressurization were found as a function of compressive loading. In conclusion, our compression device has been validated for the noninvasive response-to-loading assessment of human articular cartilage by MRI in a close-to-physiological experimental setting. Thus, in a basic research context cartilage may be functionally evaluated beyond mere static analysis and in reference to histology and biomechanics.

Long-term clinical evaluation of the automatic stance-phase lock-controlled prosthetic knee joint in young adults with unilateral above-knee amputation.

PURPOSE: The purpose of this study was to clinically evaluate the automatic stance-phase lock (ASPL) knee mechanism against participants' existing weight-activated braking (WAB) prosthetic knee joint. METHOD: This prospective crossover study involved 10 young adults with an above-knee amputation. Primary measurements consisted of tests of walking speeds and capacity. Heart rate was measured during the six-minute walk test and the Physiological Cost Index (PCI) which was calculated from heart rate estimated energy expenditure. Activity was measured with a pedometer. User function and quality of life were assessed using the Lower Limb Function Questionnaire (LLFQ) and Prosthetic Evaluation Questionnaire (PEQ). Long-term follow-up over 12 months were completed. RESULTS: Walking speeds were the same for WAB and APSL knees. Energy expenditure (PCI) was lower for the ASPL knees (p = 0.007). Step counts were the same for both knees, and questionnaires indicated ASPL knee preference attributed primarily to knee stability and improved walking, while limitations included terminal impact noise. Nine of 10 participants chose to keep using the ASPL knee as part of the long-term follow-up. CONCLUSIONS: Potential benefits of the ASPL knee were identified in this study by functional measures, questionnaires and user feedback, but not changes in activity or the PEQ.

Musculoskeletal multi-body dynamic simulation on patient-specific total knee replacement during right-turn gait / 医用生物力学

Objective To develop a musculoskeletal multi-body dynamic model of the patient-specific total knee replacement (TKR), and to simulate knee joint biomechanical characters of the patient during right-turn gait. Methods Based on the musculoskeletal dynamic software AnyBody and the method of force-dependent kinematics as well as the related data from a patient with TKR, the corresponding patient specific lower extremity musculoskeletal multi-body dynamic model was constructed and then used to simulate the right-turn gait of the patient. The knee contact forces, motion, muscle activations and ligament forces were predicted simultaneously by inverse dynamics analysis on such right-turn gait. ResultsThe root mean square error of the predicted average tibiofemoral medial contact force and lateral contact force were 285 N and 164 N, respectively, and the correlation coefficients were 0.95 and 0.61, respectively. The predicted average patellar contact force was 250 N. The predicted contact forces and muscle activations were consistent with those in vivo measurements obtained from the patient. In addition, the model also predicted the average range of tibiofemoral rotations of flexion-extension, internal-external, varus-valgus as 3°-47°, -3.4°-1.5°, 0.2°--1.5°, and the average range of tibiofemoral translations of anterior-posterior, inferior-superior, medial-lateral as 2.6-9 mm, 1.6-3.2 mm, 4.2-5.2 mm, respectively. The predicted average peak value of the medial, lateral collateral ligament force and posterior cruciate ligament force were 190, 108, 108 N, respectively. Conclusions The developed model can predict in vivo knee joint biomechanics, which offers a robust computational platform for future study on the failure mechanisms of knee prosthesis in clinic.

Tribological characteristics of polyethylene glycol (PEG) as a lubricant for wear resistance of ultra-high-molecular-weight polyethylene (UHMWPE ) in artificial knee join.

For the longevity of total knee joint prostheses, we have developed an artificial lubricant using polyethylene glycol (PEG) for the prevention of wear of ultra-high-molecular-weight polyethylene (UHMWPE). In the present study, the lubricative function of this PEG lubricant was evaluated by a wear test using Co-Cr alloy and UHMWPE counter surface samples. As a result, human synovial fluid including the PEG lubricant showed good result regarding the wear volume and a worn surface of UHMWPE. Considering its lubrication mechanism, it is suspected that interaction between the PEG molecules and the proteins in synovial fluid was involved. Since PE molecules are also organic compounds having a hydroxyl group at one or both ends, the albumin and PEG molecule complex would have bound more strongly to the metal oxide surface and UHMWPE surfaces might enhance and stabilize the lubricating film between the contact surfaces under the boundary lubrication. This study suggests that PEG lubricant as an intra-articular viscous supplement has the potential to prevent wear of UHMWPE by mixing with synovial fluid and to contribute to the longevity of knee joint prostheses.

Total knee arthroplasty:Goodness-of-fit analysis of intraoperative knee society score of Peking Union Medical College / 中国组织工程研究

BACKGROUND:Knee society score of Peking Union Medical Col ege has been promoted and used in the 306th Hospital of PLA for 2 years and we have accumulated some clinical data. OBJECTIVE:To analyze the stability and feasibility for suitable clinical medical practice of knee society score of Peking Union Medical Col ege. METHODS:Fifty-five patients with osteoarthritis of the knee were included, and the patients were divided into three groups:the preoperative group;3 months postoperative fol ow-up group;6 months postoperative fol ow-up group. The measurement results obtained by the application of the scale were compared to those of the Western Ontario and McMaster Universityies Ostroarthritis Index, visual analog scale, and hospital for special surgery score, and then knee society score goodness-of-fit analysis was performed based on the structural equation model. RESULTS AND CONCLUSION:Knee society score performance assessment of the signs and symptoms of osteoarthritis of the knee patients was positively correlated with the pain severity of visual analog scale score;the overal knee society score of the patients after 6-month fol ow-up was significantly improved compared with that before treatment. The knee society score after 3-and 6-month fol ow-up was significantly higher than that before treatment, and the score was quite with the hospital for special surgery score. The overal assessment of the knee society score after treated for 3 and 6 months was improved for more than grade Ⅰ, the visual analog scale score was decreased for more than 30%. The pain assessment items and physiological functional assessment items of Western Ontario and McMaster Universityies Ostroarthritis Index after 6-month fol ow-up were significantly better than those before treatment (Pgoodness-of-fit analysis showed that the scale had good goodness which had scientific nature and application value.