Wear of ultra-high molecular weight polyethylene (UHMWPE) in total knee prostheses: a review of key influences

On the concerning early failure of a short stem press-fit humeral component

BACKGROUND

Anatomic total shoulder arthroplasty (TSA) is a common surgical intervention for various shoulder pathologies, predominantly glenohumeral osteoarthritis. While generally considered safe and effective, complications remain a challenge. Short stem implants, aim to preserve bone stock and reduce complications. However, concerns about a specific short stem implant (Univers Apex; Arthrex, Naples, FL, USA) have surfaced due to high reported rates relatively early aseptic loosening.

METHODS

This retrospective study analyzed 116 consecutive TSA patients with Univers Apex implants from 2004 to 2022. Fifteen revision cases were assessed for radiographic loosening and explanted implants were examined for damage using a 0-3 scale. Histopathological analysis evaluated cellular responses to wear debris.

RESULTS

Of the patients, 13% (15/116) required revision at 23.2 months on average. A distinct radiographic loosening pattern was identified, with humeral component subsidence and thinning of the proximal humeral cortex. Histopathology revealed a robust inflammatory response to wear debris, with a potential association between macrophage infiltration, hinge damage, and polyethylene wear.

CONCLUSION

This study reveals a notable rate of early aseptic humeral loosening with the Univers Apex short stem implant, emphasizing concerns raised in previous reports and providing a potential explanation for the high rate of early failure. Surgeons should exercise caution and closely monitor patients with this implant design.

Linear and Volumetric Polyethylene Wear Patterns after Primary Cruciate-Retaining Total Knee Arthroplasty Failure: An Analysis Using Optical Scanning and Computer-Aided Design Models

(1) Background: Analyses of retrieved inserts allow for a better understanding of TKA failure mechanisms and the detection of factors that cause increased wear. The purpose of this implant retrieval study was to identify whether insert volumetric wear significantly differs among groups of common causes of total knee arthroplasty failure, whether there is a characteristic wear distribution pattern for a common cause of failure, and whether nominal insert size and component size ratio (femur-to-insert) influence linear and volumetric wear rates. (2) Methods: We digitally reconstructed 59 retrieved single-model cruciate-retaining inserts and computed their articular load-bearing surface wear utilizing an optical scanner and computer-aided design models as references. After comprehensively reviewing all cases, each was categorized into one or more of the following groups: prosthetic joint infection, osteolysis, clinical loosening of the component, joint malalignment or component malposition, instability, and other isolated causes. The associations between volumetric wear and causes of failure were estimated using a multiple linear regression model adjusted for time in situ. Insert linear penetration wear maps from the respective groups of failure were further processed and merged to create a single average binary image, highlighting a potential wear distribution pattern. The differences in wear rates according to nominal insert size (small vs. medium vs. large) and component size ratio (≤1 vs. >1) were tested using the Kruskal-Wallis test and the Mann-Whitney test, respectively. (3) Results: Patients with identified osteolysis alone and those also with clinical loosening of the component had significantly higher volumetric wear when compared to those without both causes (p = 0.016 and p = 0.009, respectively). All other causes were not significantly associated with volumetric wear. The instability group differentiated from the others with a combined peripheral antero-posterior wear distribution. Linear and volumetric wear rates showed no significant differences when compared by nominal insert size (small vs. medium vs. large, p = 0.563 and p = 0.747, respectively) or by component (femoral-to-insert) size ratio (≤1 vs. >1, p = 0.885 and p = 0.055, respectively). (4) Conclusions: The study found increased volumetric wear in cases of osteolysis alone, with greater wear when combined with clinical loosening compared to other groups. The instability group demonstrated a characteristic peripheral anterior and posterior wear pattern. Insert size and component size ratio seem not to influence wear rates.

Projections and Epidemiology of Revision Hip and Knee Arthroplasty in the United States to 2040-2060

Background

National projections of future joint arthroplasties are useful in understanding the changing burden of surgery and related outcomes on the health system. The aim of this study is to update the literature by producing Medicare projections for revision total joint arthroplasty procedures from 2040 through 2060.

Methods

The study uses 2000-2019 data from the CMS Medicare Part-B National Summary and combines procedure counts using CPT codes for revision total joint arthroplasty procedures. In 2019, revision total knee arthroplasty (rTKA) and revision total hip arthroplasty (rTHA) procedures totaled 53,217 and 30,541, respectively, forming a baseline from which we generated point forecasts between 2020 and 2060 and 95% forecast intervals (FI).

Results

On average, the model projects an annual growth rate of 1.77% for rTHAs and 4.67% for rTKAs. By 2040, rTHAs were projected to be 43,514 (95% FI = 37,429-50,589) and rTKAs were projected to be 115,147 (95% FI = 105,640-125,510). By 2060, rTHAs was projected to be 61,764 (95% FI = 49,927-76,408) and rTKAs were projected to be 286,740 (95% FI = 253,882-323,852).

Conclusions

Based on 2019 total volume counts, the log-linear exponential model forecasts an increase in rTHA procedures of 42% by 2040 and 101% by 2060. Similarly, the estimated increase for rTKA is projected to be 149% by 2040 and 520% by 2060. An accurate projection of future revision procedure demands is important to understand future healthcare utilization and surgeon demand. This finding is only applicable to the Medicare population and demands further analysis for other population groups.

A Comparison of Wear Patterns on Retrieved and Simulator-Tested Total Knee Replacements

Aseptic implant loosening is the most common reason for revision surgery after total knee replacement. This is associated with adverse biological reactions to wear debris from the articulating implant components. To predict the amount of wear debris generated in situ, standard wear testing of total knee replacement (TKR) is carried out before its clinical use. However, wear data reported on retrievals of total knee replacement (TKR) revealed significant discrepancies compared with standard wear simulator studies. Therefore, the aim of the present study was to compare the wear patterns on identical posterior-cruciate-retaining TKR designs by analyzing retrieved and experimentally tested implants. The identification and classification of wear patterns were performed using 21 retrieved ultra-high-molecular-weight-polyethylene (UHMW-PE) inserts and four sets of inserts of identical design and material tested in a knee wear simulator. These four sets had undergone different worst-case conditions and a standard test in a wear simulator according to ISO 14243-1. Macroscopic and microscopic examinations of the polyethylene inserts were performed, including the determination of seven modes of wear that correspond to specific wear patterns, the calculation of wear areas, and the classification of the damage over the whole articulating area. Retrieved and standard wear simulator-tested UHMW-PE inserts showed significant differences in wear area and patterns. The total wear areas and the damage score were significantly larger on the retrievals (52.3% versus 23.9%, 32.7 versus 22.7). Furthermore, the range of wear patterns found on the retrievals was not reproducible in the simulator-tested inserts. However, good correspondence was found with the simulator-tested polyethylene inserts under worst-case conditions (third body wear), i.e., deep wear areas could be replicated according to the in vivo situation compared with other wear test scenarios. Based on the findings presented here, standard simulator testing can be used to directly compare different TKR designs but is limited in the prediction of their in situ wear. Preclinical wear testing may be adjusted by worst-case conditions to improve the prediction of in situ performance of total knee implants in the future.

Mid-Term Survival of Total Hip Arthroplasty in Patients Younger Than 55-year-old

BACKGROUND

Survivorship of total hip arthroplasty (THA) in younger patients is concerning given the inverse relationship between age and lifetime risk for revision. The purpose of this study is to determine if risk of revision has improved for patients aged 55 years or younger who undergo primary THA using modern polyethylene liners.

METHODS

A retrospective review identified 2,461 consented patients (2,814 hips) with minimum 2-year follow-up who underwent primary THA at our institution between September 2007 and August 2014 using components from a single manufacturer (Zimmer Biomet), all with vitamin E-infused highly crosslinked polyethylene acetabular inserts. There were 561 patients (643 THA; 23%) aged 55 or younger and 1,900 (2,171 THA; 77%) older than 55.

RESULTS

Mean follow-up was 5.0 years for both groups. There were more male patients in the younger (55%) than older (41%) group. Body mass index (BMI) was higher in younger patients independent of gender. Improvement in Harris hip score (HHS) was similar between groups. Kaplan-Meier survival to endpoint of all cause revision was similar between groups at 12 years (P = .8808) with 97.5% (95% CI: ±0.7%) for younger versus 97.1% (95% CI: ±0.6%) for older patients. Most frequent reason for revision overall was periprosthetic femoral fracture (21; 0.75%); univariate analysis revealed risk factors were female gender (P = .28) and age ≥65 years (P = .012).

CONCLUSION

Use of modern polyethylene, such as vitamin E-stabilized highly cross-linked, liners during THA may improve survivorship in younger patients undergoing THA. Younger patients undergoing primary THA with highly cross-linked polyethylene liners had no increased rate of revision at mid-term follow-up.

Surface wear in a custom manufactured temporomandibular joint prosthesis

The wear of a novel temporomandibular joint (TMJ) prosthesis was evaluated in an animal model. The prosthesis consisted of an additively manufactured titanium alloy (Ti₆Al₄V) mandibular condyle and glenoid fossa created through selective laser melting, with a machined vitamin E‐enriched ultra‐high molecular weight polyethylene (UHMWPE) surface attached to the fossa. Thirteen TMJ prosthesis were implanted in sheep, six of which had condylar heads coated with HadSat® diamond‐like carbon (H‐DLC). Euthanasia took place after 288 days, equaling 22 years of human mastication. Linear and volumetric wear analysis of the fossa was performed by optical scanning. The condylar head surfaces were assessed by scanning electron and confocal laser microscopy. The average linear UHMWPE wear, when combined with the coated condyle, was 0.67 ± 0.28 mm (range: 0.34–1.15 mm), not significantly differing (p = .3765, t‐test) from the non‐coated combination average (0.88 ± 0.41 mm; range: 0.28–1.48 mm). The respective mean volumetric wear volumes were 25.29 ± 11.43 mm³ and 45.85 ± 22.01 mm³, not significantly differing (p = .1448, t‐test). Analysis of the coated condylar surface produced a mean Ra of 0.12 ± 0.04 μm and Sa of 0.69 ± 0.07 μm. The non‐coated condylar surface measured a mean Ra of 0.28 ± 0.17 μm and Sa of 2.40 ± 2.08 μm. Both Sa (p = .0083, Mann–Whitney U test) and Ra (p = .0182, Mann–Whitney U test), differed significantly. The prosthesis exhibits acceptable wear resistance and addition of the H‐DLC‐coating significantly improved long‐term condylar surface smoothness.

Exploring the lubrication mechanisms of synovial fluids for joint longevity - A perspective

Synovial fluids are complex fluids responsible for the exceptional lubrication present in synovial joints. These fluids consist of various constituents, including hyaluronic acid, surface-active proteins (i.e., lubricin), surface-active phospholipids, as well as various other proteins such as human serum albumin and γ -globulin seric proteins, each of them playing an essential role in lubrication. Being the key to the most efficient biotribological systems, this article is intended to review the current understanding of the underlying lubrication mechanisms of the synovial fluids enables prospective usage in numerous applications, especially as a lubricant for hip and knee prosthetics in combatting osteoarthritis. Current research focuses on the determination of the role of proteins in prosthetic lubrication, optimal material combinations for prosthesis, and the effects of relevant physical variables in prosthetic lubrication. The characterization of prosthetic lubrication and wear mechanisms by synovial fluids represents a prominent challenge in tribological research, yet also an important hurdle to overcome towards optimal lubrication of articular prosthetics.

Projections and Epidemiology of Revision Hip and Knee Arthroplasty in the United States to 2030

BACKGROUND

As the incidence of primary total joint arthroplasty rises in the United States, it is important to investigate how this will impact rates of revision arthroplasty. The purpose of this study was to analyze the incidence and future projections of revision total hip arthroplasty (rTHA) and revision total knee arthroplasty (rTKA) to 2030. Anticipating surgical volume will aid surgeons in designing protocols to efficiently and effectively perform rTHA/rTKA.

METHODS

The national inpatient sample was queried from 2002 to 2014 for all rTHA/rTKA. Using previously validated measures, Poisson and linear regression analyses were performed to project annual incidence of rTHA/rTKA to 2030, with subgroup analyses on modes of failure and age.

RESULTS

In 2014, there were 50,220 rTHAs and 72,100 rTKAs. From 2014 to 2030, rTHA incidence is projected to increase by between 43% and 70%, whereas rTKA incidence is projected to increase by between 78% and 182%. The 55-64 and 65-74 age groups increased in revision incidence during the study period, whereas 75-84 age group decreased in incidence. For rTKA, infection and aseptic loosening are the 2 most common modes of failure, whereas periprosthetic fracture and infection are most common for rTHA.

CONCLUSION

The incidence of rTHA/rTKA is projected to increase, particularly in young patients and for infection. Given the known risk factor profiles and advanced costs associated with revision arthroplasty, our projections should encourage institutions to generate revision-specific protocols to promote safe pathways for cost-effective care that is commensurate with current value-based health care trends.

LEVEL OF EVIDENCE

IV.

Spherical center and rotating platform hinged knee prosthesis: Finite-element model establishment, verification and contact analysis

BACKGROUND

Biomechanical study is fundamental for the preclinical evaluation of knee prostheses. However, there are few reports on the contact characteristic investigation in the hinged knee prosthesis. The purpose of this study was to investigate the contact characteristics of a novel hinged knee prosthesis.

METHODS

All of the component models were designed and assembled using Solidworks. A comparison of the contact area and ultra-high-molecular-weight polyethylene (UHMWPE) deformation using the experimental method (EM) and finite-element analysis (FEA) under 3000 N with the prosthesis at different flexions was performed. The peak contact pressure and von Mises stress on tibial insert and bushing were investigated under nine specific samples that were extracted from a gait cycle using FEA (according to ISO 14243-1: 2009).

RESULTS

The largest contact area and UHMWPE deformation were 100.78 ± 8.71 mm² and 0.085 ± 0.015 mm in the EM, and 96.68 mm² and 0.096 mm in FEA. The peak contact pressure and von Mises stress on the tibial insert were 26.3071 MPa and 10.5115 MPa at 13% of the gait cycle and on bushing were consistently 0 MPa. The contact pressures were distributed at the posterior of the insert.

CONCLUSION

The finite-element model was validated to be applicable for predicting the real prosthesis behavior based on the good correlation of the results using the EM and FEA. The model can help to identify contact characteristics and be can used in optimization studies of this novel prosthesis during the design phase.

Influence of Congruency Design on the Contact Stress of a Novel Hinged Knee Prosthesis Using Finite Element Analysis

Objectives

To investigate the contact stress and the contact area o tibial inserts and bushings with respect to different congruency designs in a spherical center axis and rotating bearing hinge knee prosthesis under gait cycle loading conditions using finite element analysis.

Methods

Nine prostheses with different congruency (different degrees of tibiofemoral conformity and different distances between the spherical center and the bushing) designs were developed with the same femoral and tibial components. The models were transferred to finite element software. The peak contact stresses and contact areas on tibial inserts and bushings under the gait cycle loading conditions were investigated and compared.

Results

For tibial insert, the peak contact stress was the highest in the low conformity‐long group (61.4486 MPa), and it was 1.88 times higher than that in the group with the lowest stress (moderate conformity‐short group, 32.754 MPa). The contact area was the largest in the low conformity‐long group (420.485 mm²), and it was 1.19 times larger than that in the group with the smallest area (moderate conformity‐middle group, 352.332 mm²). For bushing, the peak contact stress was the highest in the high conformity‐long group (72.8093 MPa), and it was 3.21 times higher than that in the group with the lowest stress (high conformity‐short group, 22.6928 MPa). The contact area was the largest in the low conformity‐short group (2.41 mm²), and it was 2.27 times larger than that in the group with the smallest area (high conformity‐middle group, 1.063 mm²).

Conclusion

The results of our study showed that the congruency of the tibiofemoral surface and bushing surface should be considered carefully in the design of the spherical center axis and rotating bearing hinge knee prosthesis. Different levels of contact performance were observed with different congruency designs. In addition, the influence of contact stress and contact area on the polyethylene wear of rotating hinge knee prostheses should be confirmed with additional laboratory tests.

Comportamiento ante el desgaste por deslizamiento en seco del acero inoxidable súper dúplex en un tribómetro bola sobre anillo

En el presente trabajo se realiza la caracterización del comportamiento ante el desgaste por deslizamiento en seco de un acero inoxidable súper dúplex. Los ensayos fueron desarrollados en un tribómetro tipo bola sobre anillo. Como material del anillo se empleó el acero inoxidable dúplex tipo SAF 2507 sin tratamiento térmico y como material para la bola se usó el acero AISI 52100. Los ensayos se realizaron sin lubricante en condiciones de ambiente (aire), temperatura y humedad estándar de laboratorio. Los parámetros seleccionados, a fin de estudiar sus efectos en el coeficiente desgaste por deslizamiento, fueron: velocidad de deslizamiento (0,9 m/s  y 2 m/s),  carga normal  (9 N, 19 N y 29 N) y distancias de deslizamiento (500 m, 1000 m y 2000 m). Se empleó un diseño experimental de Taguchi con nueve tratamientos y dos réplicas. En la caracterización del acero SAF 2507 se obtuvo valores del coeficiente de desgaste en el intervalo desde 0,19588 x 10-12 m2/N hasta 0,72381 x 10-12 m2/N, para las condiciones evaluadas. El factor que más afecta el coeficiente de desgaste es la velocidad de deslizamiento. El mecanismo de desgaste identificado para el SAF 2507 es de adhesión y delaminación de alta velocidad.

What Is the Incidence of Cobalt-Chromium Damage Modes on the Bearing Surface of Contemporary Femoral Component Designs for Total Knee Arthroplasty?

BACKGROUND

The purpose of this study was to determine the incidence of metal release in contemporary total knee arthroplasty and the patient-related factors associated with this release.

METHODS

In total, 256 retrieved cobalt-chromium femoral components were collected through a multi-institutional orthopedic implant retrieval program (implanted: 1-15 years). Implants were mainly revised for loosening (84/256), instability (62/256), and infection (46/256). Third-body damage was assessed using a semiquantitative scoring method. Microscale electro-corrosion damage (MECD) was evaluated using digital optical microscopy. Radii of curvature were measured from representative components to calculate anterior-posterior and medial-lateral ratios. Femoral component surface roughness was measured using a white light interferometer. Using a multivariable linear model, associations between damage score, implant, and patient factors were tested. Spearman's ρ correlation tests were performed to determine the association between roughness measurements and damage score.

RESULTS

Mild to severe damage was observed in 52% (134/256) of the components. In the multivariable linear model, anterior-posterior ratio (β = -8.07; P < .001), loosening (β = -0.52; P = .006), and patient weight (β = 0.01; P = .007) were associated with damage score. Suspected MECD damage was observed in 82% (209/256) of components. The R_a value (ρ = 0.196; P = .002) and R_q value (ρ = 0.157; P = .012) increased as the damage score increased.

CONCLUSION

The findings of this retrieval study support that similar damage mechanisms exist in contemporary and long-term total knee arthroplasty devices. Additionally, we observed associations between loosening, anterior-posterior conformity, and patient weight with increased surface damage.

An Improved Tibial Force Sensor to Compute Contact Forces and Contact Locations In Vitro After Total Knee Arthroplasty

Contact force imbalance and contact kinematics (i.e., motion of the contact location in each compartment during flexion) of the tibiofemoral joint are both important predictors of a patient's outcome following total knee arthroplasty (TKA). Previous tibial force sensors have limitations in that they either did not determine contact forces and contact locations independently in the medial and lateral compartments or only did so within restricted areas of the tibial insert, which prevented them from thoroughly evaluating contact force imbalance and contact kinematics in vitro. Accordingly, the primary objective of this study was to present the design and verification of an improved tibial force sensor which overcomes these limitations. The improved tibial force sensor consists of a modified tibial baseplate which houses independent medial and lateral arrays of three custom tension-compression transducers each. This sensor is interchangeable with a standard tibial component because it accommodates tibial articular surface inserts with a range of sizes and thicknesses. This sensor was verified by applying known loads at known locations over the entire surface of the tibial insert to determine the errors in the computed contact force and contact location in each compartment. The root-mean-square errors (RMSEs) in contact force are ≤ 6.1 N which is 1.4% of the 450 N full-scale output. The RMSEs in contact location are ≤ 1.6 mm. This improved tibial force sensor overcomes the limitations of the previous sensors and therefore should be useful for in vitro evaluation of new alignment goals, new surgical techniques, and new component designs in TKA.

Analysis of Carbon Fiber Reinforced PEEK Hinge Mechanism Articulation Components in a Rotating Hinge Knee Design: A Comparison of In Vitro and Retrieval Findings

Carbon fiber reinforced poly-ether-ether-ketone (CFR-PEEK) represents a promising alternative material for bushings in total knee replacements, after early clinical failures of polyethylene in this application. The objective of the present study was to evaluate the damage modes and the extent of damage observed on CFR-PEEK hinge mechanism articulation components after in vivo service in a rotating hinge knee (RHK) system and to compare the results with corresponding components subjected to in vitro wear tests. Key question was if there were any similarities or differences between in vivo and in vitro damage characteristics. Twelve retrieved RHK systems after an average of 34.9 months in vivo underwent wear damage analysis with focus on the four integrated CFR-PEEK components and distinction between different damage modes and classification with a scoring system. The analysis included visual examination, scanning electron microscopy, and energy dispersive X-ray spectroscopy, as well as surface roughness and profile measurements. The main wear damage modes were comparable between retrieved and in vitro specimens (n = 3), whereby the size of affected area on the retrieved components showed a higher variation. Overall, the retrieved specimens seemed to be slightly heavier damaged which was probably attributable to the more complex loading and kinematic conditions in vivo.

Posterior cruciate ligament balancing in total knee arthroplasty: a numerical study with a dynamic force controlled knee model

Background

Adequate soft tissue balancing is a key factor for a successful result after total knee arthroplasty (TKA). Posterior cruciate ligament (PCL) is the primary restraint to posterior translation of the tibia after cruciate retaining TKA and is also responsible for the amount of joint compression. However, it is complex to quantify the amount of ligament release with its effects on load bearing and kinematics in TKA and limited both in vivo and in vitro. The goal of this study was to create a dynamic and deformable finite element model of a full leg and analyze a stepwise release of the PCL regarding knee kinematics, pressure distribution and ligament stresses.

Methods

A dynamic finite element model was developed in Ansys V14.0 based on boundary conditions of an existing knee rig. A cruciate retraining knee prosthesis was virtually implanted. Ligament and muscle structures were simulated with modified spring elements. Linear elastic materials were defined for femoral component, inlay and patella cartilage. A restart algorithm was developed and implemented into the finite element simulation to hold the ground reaction force constant by adapting quadriceps force. After simulating the unreleased PCL model, two models were developed and calculated with the same boundary conditions with a 50% and 75% release of the PCL stiffness.

Results

From the beginning of the simulation to approximately 35° of flexion, tibia moves posterior related to the femur and with higher flexion anteriorly. Anterior translation of the tibia ranged from 5.8 mm for unreleased PCL to 3.7 mm for 75% PCL release (4.9 mm 50% release).

A decrease of maximum von Mises equivalent stress on the inlay was given with PCL release, especially in higher flexion angles from 11.1 MPa for unreleased PCL to 8.9 MPa for 50% release of the PCL and 7.8 MPa for 75% release.

Conclusions

Our study showed that dynamic FEM is an effective method for simulation of PCL balancing in knee arthroplasty. A tight PCL led in silico to more anterior tibia translation, a higher collateral ligament and inlay stress, while retropatellar pressure remained unchanged. Surgeons may take these results in vivo into account.

Glenoid articular conformity affects stress distributions in total shoulder arthroplasty

BACKGROUND

The stress applied to the glenoid component in total shoulder arthroplasty (TSA) remains an important concern because of the risk of wear and loosening. The purpose of this study was to determine the stress pattern in the glenoid component with 3 different surface designs.

METHODS

Computer models of 9 scapulae of patients scheduled for TSA were created from computerized tomography images. Each glenoid was virtually reamed, and 3 different glenoid component designs (conforming, nonconforming, and hybrid) were placed. Using finite element analysis, superior translation of the humeral head was modeled. Maximum stress and shear stress were measured at 3 different locations in the glenoid component: center, transition, and superior regions.

RESULTS

All 3 designs showed a similar level of maximum stress at the center and transition regions, while the maximum stress at the superior periphery was significantly higher in the conforming design than in the other 2 designs (P = .0017). The conforming design showed significantly higher shear stress at the superior periphery (P < .0001).

DISCUSSION

Stress from periphery loading is higher than from the center and transition region regardless of component design and is highest in the conforming design. The stress at the transition region of the hybrid design was not higher than the other 2 designs. The hybrid design has favorable characteristics based on its low stress at the periphery and greater contact area with the humeral head at the center.

LEVEL OF EVIDENCE

Basic Science Study, Biomechanical Computer Simulation Study.

Surface damage versus tibial polyethylene insert conformity: a retrieval study

BACKGROUND

Surface damage of the tibial polyethylene insert in TKA is thought to diminish with increasing conformity, based on computed lower contact stresses. Added constraint from higher conformity may, however, result in greater forces in vivo.

QUESTIONS/PURPOSES

We therefore determined whether increased conformity was associated with increased surface pitting, delamination, creep, and polishing in a group of retrieved tibial inserts.

METHODS

We compared 38 inserts with a dished articular surface (conforming group) with 31 inserts that were unconstrained and nonconforming in the sagittal plane (less conforming group). The two groups had identical polyethylene composition and processing history. The articulating surfaces were scored for pitting, delamination, deformation/creep, and polishing. Evidence of edge loading and the presence of embedded bone cement were also recorded.

RESULTS

The conforming inserts were associated with higher delamination and pitting scores but lower polishing scores, even after adjusting for the effects of sex, age, insert thickness, and implantation duration. Long implantation duration and male sex were also associated with increased delamination, pitting, and polishing, whereas long shelf life was associated only with increased delamination. The conforming group also had approximately a fourfold greater prevalence of edge loading and approximately a threefold greater prevalence of embedded bone cement. The latter was associated with higher scores and proportions of delamination and pitting.

CONCLUSIONS

These findings suggest more conformity may increase surface fatigue damage in TKA. Higher constraint-induced stresses during secondary motions and more possibility for edge loading and bone cement capture on a dished surface may account for these results.

CLINICAL RELEVANCE

The selection of materials with high fatigue resistance may be particularly important for high-conformity/constraint tibial inserts. In addition, awareness of the benefits and trade-offs with conformity may allow better matching of TKA design to patient.

In vivo oxidation contributes to delamination but not pitting in polyethylene components for total knee arthroplasty

The aim of this study was to better understand how in vivo oxidation contributes to fatigue damage in total knee arthroplasty (TKA). A total of 119 tibial inserts were consecutively collected after revision surgery. Of the 119 polyethylene retrievals, 29 were gamma sterilized in air (historical), whereas the remaining 90 were gamma sterilized in nitrogen (conventional). Surface damage assessment and characterization of oxidation were performed on all the retrievals. Delamination was significantly more prevalent and extensive in the longer-term, highly oxidized, historical tibial inserts. Pitting damage, in contrast, seemed to be equally prevalent between both retrieval groups and was not correlated with in vivo oxidation. Our findings support our hypothesis that in vivo oxidation is a contributing factor to delamination, but not pitting, in TKA. Despite the lower oxidation displayed by conventional retrievals, this study provides strong evidence that delamination secondary to in vivo oxidation may occur during the second decade of implantation.

Material and surface factors influencing backside fretting wear in total knee replacement tibial components

Retrieval studies have shown that the interface between the ultra-high molecular weight polyethylene insert and metal tibial tray of fixed-bearing total knee replacement components can be a source of substantial amounts of wear debris due to fretting micromotion. We assessed fretting wear of polyethylene against metal as a function of metal surface finish, alloy, and micromotion amplitude, using a three-station pin-on-disc fretting wear simulator. Overall, the greatest reduction in polyethylene wear was achieved by highly polishing the metal surface. For example, highly polished titanium alloy surfaces produced nearly 20 times less polyethylene wear compared with blasted titanium alloy, whereas, decreasing the micromotion amplitude from 200 to 50microm produced approximately four times less polyethylene wear for the same blasted titanium alloy surface. Although the effect of the metal alloy was much smaller than the effect of metal surface roughness or the micromotion amplitude, CoCr discs produced slightly greater polyethylene fretting wear than titanium alloy discs under each condition. The results are essential in design and manufacturing decisions related to fixed-bearing total knee replacements.

An 8- to 10-year review of the Rotaglide total knee replacement

Mobile-bearing knee arthroplasty (MBKA) is an alternative to fixed-bearing knee arthroplasty. This was a retrospective study of the Rotaglide Total Knee System. We present the results of the monitoring of 77 patients (85 knees) with a median duration to failure or end of follow up of 8.5 years (range 0.4 to 10.1 years). Patients were clinically and radiologically assessed at dedicated follow up clinics. The Hospital for Special Surgery (HSS) and Knee Society Score (KSS) systems were used to describe the clinical and radiological findings. The prosthesis had an estimated survival probability of 93.5% (standard error 3.4%) at 9 years. It is associated with good rates of patient satisfaction and high scores on the HSS and KSS systems. No knees were revised for aseptic loosening. This knee replacement has a survival rate equivalent to other prostheses. It is a safe and reliable prosthesis associated with good clinical outcome.

The influence of femoral condylar lift-off on the wear of artificial knee joints

In vivo fluoroscopic studies of patients with total knee replacements (TKRs) have shown lift-off of the femoral condyles from the tibial insert. This study investigated the influence of femoral condylar lift-off on the ultra-high molecular weight polyethylene (UHMWPE) wear of fixed bearing (FB) and rotating platform mobile bearing (RP MB) total knee replacements, using a physiological knee joint simulator. In the absence of lift-off, the RP MB knees exhibited a lower wear rate of 5.2 +/- 2.2 mm3 per million cycles (mm3/MC) compared with 8.8 +/- 4.8 mm3/MC for the FB knees. The presence of femoral condylar lift-off was found to accelerate the wear of the FB and RP MB knees tested in this study to 16.4 +/- 2.9 and 16.9 +/- 2.9 mm3/MC respectively. For the RP MB knees the increase in wear rate was more marked, resulting in a similar wear rate for both designs of knee under lift-off conditions. In both cases the medial condyle displayed more wear damage. This study has shown that a small amount of abduction/adduction lift-off and medial-lateral shift increases wear and that the increase in wear is design dependent. In this simulator test, lift-off was simulated on every cycle, whereas the amount of wear and effect of lift-off clinically would depend on the frequency of occurrence of lift-off in vivo.

Wear in the Prosthetic Shoulder: Association With Design Parameters

Total replacement of the glenohumeral joint provides an effective means for treating a variety of pathologies of the shoulder. However, several studies indicate that the procedure has not yet been entirely optimized. Loosening of the glenoid component remains the most likely cause of implant failure, and generally this is believed to stem from either mechanical failure of the fixation in response to high tensile stresses, or through osteolysis of the surrounding bone stock in response to particulate wear debris. Many computational studies have considered the potential for the former, although only few have attempted to tackle the latter. Using finite-element analysis an investigation, taking into account contact pressures as well as glenohumeral kinematics, has thus been conducted, to assess the potential for polyethylene wear within the artificial shoulder. The relationships between three different aspects of glenohumeral design and the potential for wear have been considered, these being conformity, polyethylene thickness, and fixation type. The results of the current study indicate that the use of conforming designs are likely to produce slightly elevated amounts of wear debris particles when compared with less conforming joints, but that the latter would be more likely to cause material failure of the polyethylene. The volume of wear debris predicted was highly influenced by the rate of loading, however qualitatively it was found that wear predictions were not influenced by the use of different polyethylene thicknesses nor fixation type while the depth of wearing was. With the thinnest polyethylene designs (2mm) the maximum depth of the wear scar was seen to be upwards of 20% higher with a metal-backed fixation as opposed to a cemented design. In all-polyethylene designs peak polymethyl methacrylate tensile stresses were seen to reduce with increasing polyethylene thickness. Irrespective of the rate of loading of the shoulder joint, the current study indicates that it is possible to optimize glenoid component design against abrasive wear through the use of high conformity designs, possessing a polyethylene thickness of at least 6mm.

Elasto-plastic contact analysis of an ultra-high molecular weight polyethylene tibial component based on geometrical measurement from a retrieved knee prosthesis

The wear phenomenon of ultra-high molecular weight polyethylene (UHMWPE) in knee and hip prostheses is one of the major restriction factors on the longevity of these implants. Especially in retrieved knee prostheses with anatomical design, the predominant types of wear on UHMWPE tibial components are delamination and pitting. These fatigue wear patterns of UHMWPE are believed to result from repeated plastic deformation owing to high contact stresses. In this study, the elasto-plastic contact analysis of the UHWMPE tibial insert, based on geometrical measurement for retrieved knee prosthesis, was performed using the finite element method (FEM) to investigate the plastic deformation behaviour in the UHMWPE tibial component. The results suggest that the maximum plastic strain below the surface is closely related to subsurface crack initiation and delamination of the retrieved UHMWPE tibial component. The worn surface whose macroscopic geometrical congruity had been improved due to wear after joint replacement showed lower contact stress at macroscopic level.

Contact stresses in the glenoid component in total shoulder arthroplasty

Several studies of retrieved glenoid components from total shoulder arthroplasty show an erosion of the rim, surface irregularities, component fracture and wear resulting from polyethylene deformation in vivo. Particles resulting from polyethylene wear might be one of the reasons for the very high rate of glenoid component loosening found clinically. Because wear can be the result of high contact stresses, the aim of this study is to find out whether or not contact stresses are high enough to cause wear of the glenoid component and what influence the component type and geometry have on polyethylene contact stresses for different humerus abduction angles. Elasticity theory is used in a parametric study of contact stresses in several glenoid component designs. A finite element method is used to confirm the accuracy of the analytical solution. The analysis shows that the peak stress generated in glenoid components under conditions of normal living can be as high as 25 MPa; since this exceeds the polyethylene yield strength, wear and also cold flow of the components can be expected. It is predicted that more conforming components have lower contact stresses, which might result in lower wear rate and less cold flow. It is also found that a metal-backed component promotes higher contact stresses than an all-polyethylene component with the same total thickness, therefore it can be expected that metal-backed components have inferior wear properties.

The causes of insert backside wear in total knee arthroplasty

Wear of the insert backside occurs ostensibly because of micromotion at the undersurface articulation that occurs with loading. When a cyclic axial load was applied to contemporary knee implants, all inserts tested moved 2 to 25 microm in the shear plane relative to the metal backing suggesting that undersurface motion may be inevitable. Variables that increase the forces between the insert and metal backing can worsen relative micromotion and backside wear. Forces at the undersurface articulation, created during physiologic loading, are influenced by insert type, articular design, and surgical technique. Increasing articular insert constraint can cause forces at the main articulation to be resisted and transferred to this and the other interfaces. Designs with a cam post mechanism that force rollback at a certain flexion angle create a significant force in this shear plane. Inserts with highly conforming articular geometries can have a similar affect if used to inhibit anteroposterior or mediolateral motion of the femur on the tibial insert. Component alignment and position, and ligament balance also may influence backside wear as suggested by the great variability of wear patterns seen on like insert retrievals and by kinematic differences observed in fluoroscopic studies of the same implant design. Only by understanding these potential causes of backside motion and subsequent wear, can backside wear be mitigated.

How surface topography relates to materials' properties

The topography of a surface is known to substantially affect the bulk properties of a material. Despite the often nanoscale nature of the surface undulations, the influence they have may be observed by macroscopic measurements. This review explores many of the areas in which the effect of topography is macroscopically relevant, as well as introducing some recent developments in topographic analysis and control.

Factors affecting polyethylene wear in total knee arthroplasty

A complication of total knee arthroplasty (TKA) is fatigue-type wear, which can destroy a tibial inlay in <10 years. This deleterious wear mechanism occurs during cyclic loading if the yield stress of polyethylene is exceeded. Because increased stress on and within the polyethylene inlay is associated with increased wear, it is important to reduce the inlay stress by either activity restrictions or conformity changes of design. All stress parameters are more sensitive to conformity changes (eg, design changes) than to load changes (eg, activity restrictions). However, the reduction of stress on and within the polyethylene through increased conformity will increase the stress at the tibial fixation interfaces. An attempt was made to solve this problem with the introduction of mobile-bearing designs. Many mobile-bearing designs exist with good long-term results. One important difference among the various designs is the amount of flexion range with full conformity between the femoral component and the tibial inlay. Although a single radius design reduces polyethylene stress throughout the flexion range, it may be disadvantageous for a revision design to intraoperatively adapt to different degrees of constraint. Aseptic loosening and osteolysis due to small abrasive and adhesive wear particles have also been reported as a cause of failure. The design and material parameters affecting polyethylene wear in TKAs, as well as the potential detrimental effects of wear particle size, are the key issues in defining the life of a TKA.

Mobile bearings in primary knee arthroplasty

Mobile-bearing knee arthroplasty (MBKA) has potential advantages compared with conventional fixed-bearing total knee arthroplasty (TKA). By allowing unconstrained axial rotation, MBKA can offer greater articular conformity without an increased probability of loosening due to increased axial torque. Increased articular conformity minimizes polyethylene contact stresses, thereby reducing linear wear and subsurface fatigue failure. Axial rotation of the platform also enables self-correction of tibial component malrotation. Despite these advantages, the long-term clinical results obtained with current MBKA devices are similar to those obtained with well-designed fixed-bearing TKA prostheses, with no data suggesting their superiority. The disadvantages of MBKA include bearing dislocation and breakage, soft-tissue impingement, a steep technique learning curve, and concerns about volumetric wear. Hypothetically, longer-term follow-up of MBKA results may reveal a significant difference from fixed-bearing TKA results as the fatigue failure threshold of incongruent polyethylene is exceeded.

Contact stress on polyethylene components of a new rotating hinge with a spherical contact surface

OBJECTIVE

To assess the nonlinear contact stress of a new rotating hinge of our knee prosthesis at various rotation angles.

DESIGN

The contact surface between the metal tibial bearing and the ultra-high-molecular weight polyethylene plate of a conventional rotating hinge is of cylindrical design. We have designed a new type of rotating hinge with a congruous spherical contact surface.

BACKGROUND

The endoprosthesis for reconstruction of limb after wide resection of malignant tumor around knee usually incorporates a rotating hinge. Our new rotating hinge with a spherical contact surface incorporates the benefits of an increased contact surface and potentially increased rotational stability during axial loading.

METHODS

We utilized the ABAQUS finite element program to assess the nonlinear contact stress of this new rotating hinge at rotation angles of 0 degrees, 4 degrees and 8 degrees, based on a contact force of about 2800 N.

RESULTS

The results show that von Mises stress for the finite element model of the polyethylene component of this rotating hinge ranges from 4.90 x 10(-6) to 8.22 MPa at the aforementioned rotational angles. The von Mises stress is about 1.31--1.82 MPa on the major parts of the ultra-high-molecular weight polyethylene plate, including both flanks. There is a mild stress concentration on the outer edge of polyethylene component, especially at 4 degrees and 8 degrees of rotation. The maximum values of von Mises stress at the contact surface at 0 degrees, 4 degrees and 8 degrees of rotation are 5.92, 7.49 and 8.22 MPa, respectively. These contact stresses are within the safety range of the ultra-high-molecular weight polyethylene (compressive yield strength, 14 MPa).

CONCLUSIONS

This new rotating hinge has an evenly distributed contact stress during axial load because of congruous contact design.