Computational wear assessment of hard on hard hip implants subject to physically demanding tasks

Perioperative Complications after Hip and Knee Revision Arthroplasty in the over 80 Years Old Population: A Retrospective Observational Case–Control Study

Background: The number of joint revision arthroplasties has increased in the elderly population, which is burdened by several perioperative risks. Methods: Patients who underwent hip and knee revision arthroplasty were retrospectively included, and they were divided into two groups by age: <80 years old (Group 1) and ≥80 years old (Group 2). The primary outcome was to compare perioperative complication rates. The secondary outcome was to compare the 30-day, 90-day, and 1-year readmission rates. Results: In total, 74 patients in Group 1 and 75 patients in Group 2 were included. Postoperative anemia affected 13 patients in Group 1 (17.6%) and 25 in Group 2 (33.3%, p 0.027); blood units were transfused in 20 (26.7%) and 11 (14.9%, p 0.076) patients, respectively. In Group 1, two (2.7%) patients reported wound infection. In Group 2, eight (10.7%) patients presented hematomas, and two (2.7%) patients reported dislocations. No significant differences in the two groups were observed for 30-day (p 0.208), 90-day (p 0.273), or 1-year readmission rates (p 0.784). Conclusion: The revision arthroplasty procedure in patients over 80 years old is not associated with a higher risk of perioperative complications, or higher readmission rate compared with younger patients undergoing hip and knee revision surgery.

Adopted walking condition for computational simulation approach on bearing of hip joint prosthesis: review over the past 30 years

Bearing on artificial hip joint experiences friction, wear, and surface damage that impact on overall performance and leading to failure at a particular time due to continuous contact that endangers the user. Assessing bearing hip joint using clinical study, experimental testing, and mathematical formula approach is challenging because there are some obstacles from each approach. Computational simulation is an effective alternative approach that is affordable, relatively fast, and more accessible than other approaches in examining various complex conditions requiring extensive resources and several different parameters. In particular, different gait cycles affect the sliding distance and distribution of gait loading acting on the joints. Appropriate selection and addition of gait cycles in computation modelling are crucial for accurate and reliable prediction and analysis of bearing performance such as wear a failure of implants. However, a wide spread of gait cycles and loading data are being considered and studied by researchers as reported in literature. The current article describes a comprehensive literature review adopted walking condition that has been carried out to study bearing using computational simulation approach over the past 30 years. Many knowledge gaps related to adoption procedures, simplification, and future research have been identified to obtain bearing analysis results with more realistic computational simulation approach according to physiological human hip joints.

In-vitro tribological study and submodeling finite element technique in analyzing wear of zirconia toughened alumina against alumina with bio-lubricants for hip implants

Tribological study of zirconia toughened alumina against alumina is investigated using ball-on-disk tribometer with different bio-lubricants. Friction and wear coefficients are estimated for these bio-lubricants under four different loading conditions which are equivalent to regular and risky human gait activities. Experiments are carried out for a total sliding distance of 10 km with each bio-lubricant to estimate its friction and wear coefficients. Using submodeling finite element approach, cumulative linear and volumetric wear is estimated with the help of contact pressure. The sesame oil bio-lubricant showed better wear coefficient for risky gait activities and Ringer's solution exhibited minimum wear coefficient for normal walking gait activity. Overall minimum cumulative linear and volumetric wear for 2 million cycles was obtained for Ringer's solution.

The Effect of Bottom Profile Dimples on the Femoral Head on Wear in Metal-on-Metal Total Hip Arthroplasty

Wear and wear-induced debris is a significant factor in causing failure in implants. Reducing contact pressure by using a textured surface between the femoral head and acetabular cup is crucial to improving the implant’s life. This study presented the effect of surface texturing as dimples on the wear evolution of total hip arthroplasty. It was implemented by developing finite element analysis from the prediction model without dimples and with bottom profile dimples of flat, drill, and ball types. Simulations were carried out by performing 3D physiological loading of the hip joint under normal walking conditions. A geometry update was initiated based on the patient’s daily routine activities. Our results showed that the addition of dimples reduced contact pressure and wear. The bottom profile dimples of the ball type had the best ability to reduce wear relative to the other types, reducing cumulative linear wear by 24.3% and cumulative volumetric wear by 31% compared to no dimples. The findings demonstrated that surface texturing with appropriate dimple bottom geometry on a bearing surface is able to extend the lifetime of hip implants.

Finite element submodeling technique to analyze the contact pressure and wear of hard bearing couples in hip prosthesis

Finite element (FE) simulation plays a major role in computing stress and predicting the failure of biomedical components. Normally in past, researchers focused on developing a global computational model from the scanned data of patients to analyze the stresses and deformations. To compute the wear of the hip prosthesis, mostly the global model (GM) is used to predict the expected life for million cycles using nodal updating technique which leads to high computational effort and time. The proposed work utilizes a submodeling finite element technique to analyze the contact pressure and wear of biomaterials for three different combinations in hip prosthesis including metal, ceramic and polycrystalline diamond materials. Initially the global model boundary and loading conditions are transferred to the submodel. The mesh is refined further using finer mesh and then the results are computed which consumes lesser time. The contact stress as well as the linear wear of biomaterials is found to be quite high for the local model (LM) when compared with the global model. However, no changes in volumetric wear of these biomaterials are observed when compared with previous experimental results. The computational time as well as accuracy in estimating the contact stress and the wear of bearings is improved effectively. Among local model with different element sizes, 0.75 mm element size of local model showed improved results in estimating the contact stress and linear wear of bearing.

Reducing stress concentration on the cup rim of hip implants under edge loading

High stress concentration under edge loading on the cup rim contact due to micro-separation causes accelerated striping wear, fracture, and fatigue in hip implant components. While continuous effort is devoted into improving bearing design and surgical procedure to tackle the problem, the concern still has remained forcing biomedical engineers to seek for new and alternative solutions. The current paper aims to investigate the effect of a new geometry "spline" introduced at the cup's rim corner to minimise stress concentration under edge loading. Three-dimensional finite element modelling of a metal-on-metal hip implant is developed, where contact pressure, von Mises stress, and strain are predicted for three spline geometries, ie, equivalent characteristic arc radius (R = 0.5, 1.0, and 1.5 mm) at four micro-separations (of 1.0, 1.5, 2.0, and 2.5 mm) simulating edge loading on the rim contact via the application of a constant vertical load of 3 kN. The efficacy of the spline is compared with that of circular arc and sharp corner (ie, no arc) geometries. Overall, the spline outperforms both sharp corner and circular arc in reducing contact pressure, stress, and strain. The benefit of the spline over the circular arc is quite promising at larger micro-separation but fairly marginal at smaller arc radius and micro-separation. The findings indicate that, as an alternative to the circular fillet, the spline can be considered a potential geometry to be incorporated at the rim corner of the cup.

Mechanical loading characteristics of total hip prosthetics subjected to dynamic loading cycles

The selection of best material pair in the hip prosthetics design for improved performance and life relies on the estimation of hip joint contact stresses and contact pressure distribution during various dynamic loading cycles: Climbing Upstairs, Climbing downstairs and Knee bending. The maximum Von Mises stress, contact pressure and deformation are considered factors in selecting the material pair in this current study. This is done by analysis of a three-dimensional finite element model of the acetabular component during the different dynamics cycles using ANSYS®. The different material combination of bearing couples considered for this analysis are metal in contact with plastic, metal on metal, metal on ceramic, ceramic on plastic, ceramic on metal and ceramic on ceramic. The numerical results were validated by comparing them with the FEA results of Hai-Bo Jiang et al. for the existing material combinations and a high correlation of 92% was observed. We found that the Alumina femoral head paired with ultra-high molecular weight polyethylene (UHMWPE) cup reduces the maximum Von Mises stress and maximum contact pressure developed at the interface amongst other material pairs.