Polyethylene Tibial Component Research Articles

Functional assessment of all polyethylene tibial monoblock component in total knee arthroplasty

Background: In a developing country like India the cost effectiveness of all polyethylene tibial components is a major boon, without compromising the functional outcome. In this study we have attempted to evaluate the functional outcome of all polyethylene tibial monoblock component in total knee arthroplasty. Methodology: The study was carried out on 86 patients who are operated for total knee arthroplasty with all polyethylene tibial monoblock component. Demographic, surgical and follow up data was collected from case sheets of patients and copied in Performa. The patients were called for five years follow up and examined in the outpatient department. Results: The mean age of study population was 62.8 years (range 50 – 72 years) with mean BMI of 27.6 kg/m2. Statistically significant improvement was seen in the range of movements in all the age groups. Both male and female patients had insignificant difference in knee scoring. Assessment of clinical functional abilities of knee scoring have observed to be higher in patients with lower BMI. Conclusion: Significant improvement in range of motion as well as knee score in all age range, emphasizes the fact that total knee arthroplasty with all polyethylene design in osteoarthritis is an excellent surgery to restore near normal life style.

Functional assessment of all polyethylene tibial monoblock component in total knee arthroplasty

Background: In a developing country like India the cost effectiveness of all polyethylene tibial components is a major boon, without compromising the functional outcome. In this study we have attempted to evaluate the functional outcome of all polyethylene tibial monoblock component in total knee arthroplasty. Methodology: The study was carried out on 86 patients who are operated for total knee arthroplasty with all polyethylene tibial monoblock component. Demographic, surgical and follow up data was collected from case sheets of patients and copied in Performa. The patients were called for five years follow up and examined in the outpatient department. Results: The mean age of study population was 62.8 years (range 50 – 72 years) with mean BMI of 27.6 kg/m2. Statistically significant improvement was seen in the range of movements in all the age groups. Both male and female patients had insignificant difference in knee scoring. Assessment of clinical functional abilities of knee scoring have observed to be higher in patients with lower BMI. Conclusion: Significant improvement in range of motion as well as knee score in all age range, emphasizes the fact that total knee arthroplasty with all polyethylene design in osteoarthritis is an excellent surgery to restore near normal life style.

Early failure of all polyethylene tibial components in bilateral total knee arthroplasty: A case report

Introduction: Outcomes of Total Knee Arthroplasty (TKA) performed with modern all polyethylene (AP) tibial components have been reported to be comparable with or better than those TKAs performed using metal-backed modular (MBM) tibial components in several medium and long term studies. As AP components also provide substantial cost savings, there has been increase in their use in primary TKA. In spite of such good results, failure of AP tibial components has been reported.Case Presentation: A sixty three year old lady operated for bilateral cruciate retaining PFC Sigma TKA utilizing AP tibial components without patellar resurfacing in 2011 presented to us in December 2014 with two-year history of severe pain in both knees and inability to walk or stand. She had marked varus deformity of both knees. Radiological examination revealed fracture of the medial tibial plateau with failure of AP tibial component and marked varus deformity. She was treated with bilateral staged revision TKA which resulted in a satisfactory outcome. Conclusion: This case report describes previously unreported complication of AP tibial component following cruciate retaining bilateral AP tibia PFC Sigma TKA in a patient of varus osteoarthritis of knee joint. Early collapse of medial tibial plateau leading to failure of bilateral TKA, which could be attributed to under correction of varus deformity and instability, was managed with bilateral revision TKA using tibial metaphyseal sleeves which led to a very satisfactory outcome and excellent five year follow up.

A short-term study of clinical and radiological outcomes of total knee replacement using all polyethylene tibial component: A prospective observational study

Osteoarthritis (OA) of bone peripherally is frequently associated with pain, physical disability and worsening quality of life, which in turn leads to a considerable burden on the society and individuals. The surgical management of OA comprises of arthroscopy, high tibial osteotomy (HTO), unicompartmental knee arthroplasty and total knee arthroplasty (TKA). High tibial osteotomy and unicompartmental knee arthroplasty are potential alternatives if only a single compartment is involved with more data supporting unicompartmental knee arthroplasty as a good treatment option in this scenario. To conclude, early tibial component designs were almost uniformly all polyethylene and still continue to dominate the market. The total condylar designs using these tibial components have continued to show greater than 90% survivorship. No statistically significant improvement was seen in the radiological outcomes in patients undergoing All-Polyethylene tibial component at short term follow up. In this study, there was a significant improvement in the Knee society score, WOMAC score and Oxford score post operatively.

Optimal Conformity Design of Tibial Insert Component Based on ISO Standard Wear Test Using Finite Element Analysis and Surrogate Model

Total knee replacement is a standard surgical treatment used to treat osteoarthritis in the knee. The implant is complicated, requiring expensive designs and testing as well as a surgical intervention. This research proposes a technique concerning the optimal conformity design of the symmetric polyethylene tibial insert component for fixed-bearing total knee arthroplasty. The Latin Hypercube Sampling (LHS) design of the experiment was used to create 30 cases of the varied tibial insert conformity that influenced the total knee replacement wear volume. The combination of finite element analysis and a surrogate model was performed to predict wear volume according to the standard of ISO-14243:2014 wear test and to determine the optimal conformity. In the first step, the results could predict wear volume between 5.50 to 72.92 mm3/106 cycle. The Kriging method of a surrogate model has then created the increased design based on the efficient global optimization (EGO) method with improving data 10 design points. The result revealed that the optimum design of tibial insert conformity in a coronal and sagittal plane was 0.70 and 0.59, respectively, with a minimizing wear volume of 3.07 mm3/106 cycle. The verification results revealed that the area surface scrape and wear volume are similar to those predicted by the experiment. The wear behavior on the tibial insert surface was asymmetry of both sides. From this study it can be concluded that the optimal conformity design of the tibial insert component can be by using a finite element and surrogate model combined with the design of conformity to the minimized wear volume.

Primary total knee replacement using dished polyethylene with resected posterior cruciate ligament

<p><strong>Background: </strong>The choice between preserving, sacrificing or substituting the posterior cruciate ligament (PCL) is always a controversial topic in total knee replacement (TKR). Dished polyethylene insert with PCL resection enables correction of the commonly present fixed flexion and varus deformities. Additionally, the risk of premature wear of polyethylene is less because of the confirming articular geometry between the femoral and tibial component.<strong></strong></p><p><strong>Methods: </strong>This is a retrospective study in which we studied 120 knees in 95 consecutive patients undergoing primary TKR by the senior author at our institute. We used TKR system with dished metal backed polyethylene tibial component. PCL resection was performed in all cases. Pre-operative and post-operative functional assessment were done using knee society clinical scores and Western Ontario and McMaster universities osteoarthritis index (WOMAC). All radiographs were assessed using the knee society Roentgenographic scoring system (KSRES). Statistical analysis was performed using paired student t tests. Survivorship was determined using Kaplan-Meier survivorship curves. <strong></strong></p><p><strong>Results: </strong>Mean follow-up was 8 years. Range of motion increased from 75 degrees to 110 degrees. The knee society pain score increased from 30 to 94. The knee society function score increased from 35 to 75. WOMAC score increased in terms of pain, stiffness and physical function.<strong></strong></p><p><strong>Conclusions: </strong>We conclude that deep dish bearing is a viable option in presence of deficient PCL and provides adequate stability and functional outcome. We need a larger sample size, multicentre trial and longer follow-up to see for complication rate, revision rate and survival.</p>

Lateral unicompartmental knee arthroplasty: A review.

Isolated lateral compartment osteoarthritis of the knee is a rare condition affecting approximately 1% of the population, which is ten times less common than osteoarthritis affecting only the medial compartment. Unicompartmental knee arthroplasty (UKA) has many potential advantages over total knee arthroplasty. The benefits of UKA include a smaller incision, preservation of more native tissue (including cruciate ligaments and bone), decreased blood loss, and better overall proprioception. When UKA was first introduced in the 1970s, the outcomes of medial UKA (MUKA) were poor, but the few cases of lateral UKA (LUKA) showed promise. Since that time, there has been a relative paucity of literature focused specifically on LUKA given it is a rare procedure. Refinements in patient selection criteria, implant design, and surgical technique have been made leading to increased popularity. A review of the recent literature reveals that LUKA is associated with excellent long-term clinical outcomes and implant survivorship when performed in properly selected patients. Implant design options include fixed vs mobile bearing as well as metal backed vs all polyethylene tibial component, with improved outcomes noted with fixed bearing designs. Three reasons cited for revision (i.e., fracture of the femoral component, fracture of the tibial component, and valgus malalignment) had been reported in past literature but not recently. Presently, while rare, the most common cause of failure and need for revision are osteoarthritis progression and aseptic loosening. Despite the need for an occasional revision procedure, the survivorship of LUKA is comparable to MUKA, although it should be noted that outcomes of MUKA have been notably varied. Continued pursuit of improved techniques and implant designs will continue to show LUKA to be an excellent procedure for appropriately indicated patients.

Less polyethylene wear in monobloc compared to modular ultra-high-molecular-weight-polyethylene inlays in hybrid total knee arthroplasty: A 5-year randomized radiostereometry study

BackgroundA modular polyethylene (PE) inlay in total knee arthroplasty (TKA) may wear on both sides. PE particles may induce osteolysis, which can lead to implant loosening. The aim of this study was to determine if PE wear in monobloc TKA differs from that ofmodular TKA at 60-month follow-up. Patients and methodsIn a prospective, patient-blinded trial, 50 patients were randomized to hybrid TKA surgery with either acementless high-porosity trabecular-metal tibial component with a monobloc UHMWPE inlay (MONO-TM) or a cementless low-porosity screw-augmented titanium fiber-mesh tibial component with a modular UHMWPE inlay (MODULAR-FM). Radiostereometry was used to measure PE wear and tibial component migration. ResultsAt 60-monthfollow-up, mean PE wear of the medial compartment was 0.24 mm and 0.61 mm and mean PE wear of the lateral compartment was 0.31 mm and 0.82 mm for the MONO-TM and the MODULAR-FM groups, respectively (p < 0.01). The PE wear-rate was 0.05 mm (95% CI 0.03–0.08) in the MONO-TM group and 0.14 mm (95% CI 0.12–0.17) in the MODULAR-FM group (p < 0.01). Total translation at 60 months was mean 0.30 mm (95% CI 0.10–0.51) less (p < 0.01) for MONO-TM compared with MODULAR-FM tibial components. The majority of tibial components were stable (<0.2 mm MTPM) from 12 to 24-month and 24 to 60-month follow-up. ConclusionAt mid-term follow-up, monobloc PE inlay wear was approximately 40% of that of the modular PE inlay wear, which suggest that back-side wear of modular PE inlays is a significant contributor of PE wear in hybrid TKA.

1.5-Stage Exchange Arthroplasty for Total Knee Arthroplasty Periprosthetic Joint Infections

BackgroundPeriprosthetic joint infection (PJI) in total knee arthroplasty (TKA) is a challenging problem. The purpose of this study was to outline a novel technique to treat TKA PJI. We define 1.5-stage exchange arthroplasty as placing an articulating spacer with the intent to last for a prolonged time. MethodsA retrospective review was performed from 2007 to 2019 to evaluate patients treated with 1.5-stage exchange arthroplasty for TKA PJI. Inclusion criteria included: articulating knee spacer(s) remaining in situ for 12 months and the patient deferring a second-stage reimplantation because the patient had acceptable function with the spacer (28 knees) or not being a surgical candidate (three knees). Thirty-one knees were included with a mean age of 63 years, mean BMI 34.4 kg/m2, 12 were female, with a mean clinical follow-up of 2.7 years. Cobalt-chrome femoral and polyethylene tibial components were used. We evaluated progression to second-stage reimplantation, reinfection, and radiographic outcomes. ResultsAt a mean follow-up of 2.7 years, 25 initial spacers were in situ (81%). Five knees retained their spacer(s) for some time (mean 1.5 years) and then underwent a second-stage reimplantation; one of the five had progressive radiolucent lines but no evidence of component migration. Three knees (10%) had PJI reoccurrence. Four had progressive radiolucent lines, but there was no evidence of component migration in any knees. Conclusions1.5-stage exchange arthroplasty may be a reasonable method to treat TKA PJI. At a mean follow-up of 2.7 years, there was an acceptable rate of infection recurrence and implant durability.

Catastrophic failure of biconcave unicompartmental polyethylene bearings

BackgroundA biconcave polyethylene (PE) bearing was developed for mobile-bearing unicompartmental knee arthroplasties (UKA) to reduce PE dislocation. MethodsA modification of the BalanSys Unicompartmental knee system with a biconcave PE and convex tibial component was used in 32 prostheses in 28 patients. Clinical outcomes and five cases of PE fracture are reported and extensively analyzed ex vivo. ResultsVisual Analogue Score of pain and satisfaction, and Knee Society Scores improved for all patients. The passive range of motion was 130°. No PE bearings dislocated. Five bearings fractured with oxidation, cracking and delamination at the thinnest central region of the PE. The combination of increased stress and decreased poly thickness was associated with increased creep. PE oxidation caused embrittlement and contributed to fractures in the thin waist of the implant. ConclusionsThe unforeseen consequence of a novel design of a UKA that resulted in a specific mechanical and tribological mode of failure is reported. We conclude the PE failed due to a biconcave design that increased stress on the implant at its region of risk combined with a decrease of the polyethylene thickness by 1 mm in the central area.

Cemented all-poly tibia in resource constrained country, affordable and cost-effective care. Is it applicable at this era? Review article.

Osteoarthritis of knee is a progressive disease requiring total knee replacement in advanced stage. TKR is being performed in high numbers in developing countries as well. It carries significant economic burden on health system including high cost of implants. Initially, tibial components were cemented all polyethylene monoblock constructs. Subsequent studies showed excellent long term follow up in terms of durability up to 20 years.Successive studies reported aseptic loosening as the cause of failure but such studies failed to address factors responsible for failure other than implant. Cemented metal-backed non-modular tibial components (MBT) are implants in current use. They provide modularity in terms of polyethylene thickness, stems wedges. A literature reported cost saving of $1.17 million, by operating 16,500 total joints using all poly-tibial tibial component rather than metal backed tibial component. studies have reported no significant difference in terms of survivorship, function and backside wear.MethodsFor this study only English written articles were included. Studies included case reports, case series, RCTs and systemic reviews related to all polyethylene tibial components. Articles reporting all levels of evidence – Level I to IV- were included as part of our research. PubMed, Google Scholar and Cochrane Reviews databases from 2000 to 2016 were searched for studies.ResultsInformation was gathered and thoroughly studied from 30 articles with overall result in favor of the APTC implant.ConclusionAll polyethylene tibial component (APTC) is an appealing and cost effective alternative, and is associated with the excellent survivorship and lower risk of revision. In light of the present-day economic evidence and long-term functional outcome, all-polyethylene should be in more use than metal backed especially in resource-constrained setting.

All-Polyethylene Tibial Components in Total Knee Replacement: Early Failures.

In total primary knee replacement surgery, the use of all-polyethylene tibial (APT) components has many advantages, including no backside wear and no linear dissociation. In addition, the greater polyethylene thickness permits more conservative bone resection compared with that for metal-backed components, with a lower unit cost and similar functional results. Thus, the use of an APT in primary total knee arthroplasty remains an attractive option. This is a review of 158 patients who underwent primary knee replacement using APT components from a single manufacturer. Data collection included age, American Society of Anesthesiology physical status classification, body mass index (BMI), type of deformity, the presence of diabetes mellitus, rate of revision, and characteristics associated with early failure of the components. Average follow-up time was 40 months. The revision rate for any reason was 5.6%, and the average BMI in revision cases was 37.6. Patients with a higher BMI (≥ 37.6) were significantly more likely to require revision surgery than patients with a lower BMI (p = 0.04). In our sample, high BMI was a contributing factor for early failures in total knee replacements using an APT component. Generally, polyethylene tibial components used for primary knee replacements are safe and effective, with good outcomes and subsequent lower costs to the health care system.

Functional outcome of patients with osteoarthrosis of knee in south Indian population treated with total knee arthroplasty using all polyethylene tibial component: A prospective analysis

Introduction: Osteoarthrosis is the commonest of all joint diseases. Degenerative arthritis of the knee is a common affliction in our Indian population with major functional, medical, psychosocial and financial effects on the affected person, family and society. Knee replacement provides a way to overcome all afflictions of arthritis and is one of the most successful orthopaedic surgeries with immense patient satisfaction. Aim of the study: To analyse the functional outcome of patients with Osteoarthrosis of knee treated with Total Knee Arthroplasty using all – poly Tibial component based on the range of motion, radiological measures and associated complications.Materials and methods: This is a prospective study of Osteoarthrosis of the knee joint and treated with Total knee arthroplasty using all-poly Tibial component during the period from June 2016 to August 2018 at Rajah Muthiah Medical College Hospital. A total of 14 total knee replacements done on 14 patients were included and followed up in the study. The pre-operative status and the post-operative functional outcome and pain relief of our patients were assessed using the Knee society scoring system and Visual analogue scale respectively.Results: 12 patients had excellent results, 2 patients had good results. 12 patients were satisfied following their replacements (80%), 2 patients (20%) were not very satisfied and none of the patients were dissatisfied. The commonest complications we encountered were knee stiffness, persistent knee pain and transient foot drop.Conclusion: The results of total knee arthroplasty using all polyethylene tibial component in our study population, when treated with standard operative techniques, post-operative rehabilitation protocol, proper patient education and lifestyle modification are comparable to that of any other prosthesis used for TKR.

Comparison of CMM and Micro-CT Volumetric Analysis of Polyethylene Tibial Knee Inserts in Total Knee Replacement

Ultrahigh molecular weight polyethylene (UHMWPE) bearings are used widely in orthopaedic joint replacement as a prominent material for improving the longevity, which is dramatically influenced by wear of polyethylene. Polyethylene tibial knee components from knee simulators under two different input conditions were analyzed using CMM and Micro-CT measurement techniques for volumetric loss with gravimetric measurement as reference. Based on the coordinates and image slices obtained, the surface curve fitting and image digitization methodology were used for the creation of nominal “original” surface in the case of no prewear data provided. The comparison results indicate that gravimetric remains the gold standard and the CMM measurement took less time and had better precision, accuracy, and repeatability compared to Micro-CT measurement technique.

Radiographic assessment of distal femur cemented stems in tumor endoprostheses.

Distal femoral endoprosthesis (DFE) has become the optimal method of reconstruction in the skeletally mature patients treated for malignant bone tumor. Albeit literature has reported wide range of aseptic loosening in cemented components (6-32%), few authors showed that cement was not detrimental to long-term success of primary distal femoral implants possibly relating to cementing technique. A series of consecutive of DFE (MRS and GMRS, Styker Orthopaedics, Mahwah, NJ) was retrospectively reviewed for evidence of loosening on plain radiographs. All prostheses had the standard straight 127-mm stem and a cemented polyethylene tibial component. Cementing technique involved reaming line to line to the selected stem size and cementing without pressurization. Radiographs were assessed by two independent blinded reviewers and scored for radiolucent zones (>1mm) and graded as not loose, possibly, probable and definite loose. Furthermore, the final reamer/stem diameters, length of resection, tumor type, adjuvant treatment modalities, bushing exchange/revision surgery and infection rate were recorded. There were 70 patients and none were lost to follow-up. The average radiographic follow-up was 7.2years (58% had f/u >5years). Examiner A found 89% of femoral components to be "Not Loose" and 11% (n=6) "Possibly Loose". Examiner B found 96% of femoral components to be "Not Loose" and 4% (n=2) to be "Possibly Loose". No components scored as probably or definitely loose. Two DFE stems were reported as "Possibly Loose" by both reviewers. No femoral stem required revisions for either loosening, femur fracture or metal failure. Although infection was frequent, there was no septic loosening. Despite our study limitations, no radiographic evidence of loosening was found. Cementing distal femur prosthesis with a tight canal fit and with a thin and inconsistent cement mantle appears to be a viable option at short and medium term.

PEEK-OPTIMA™ as an alternative to cobalt chrome in the femoral component of total knee replacement: A preliminary study.

PEEK-OPTIMA™ (Invibio Ltd, UK) has been considered as an alternative joint arthroplasty bearing material due to its favourable mechanical properties and the biocompatibility of its wear debris. In this study, the potential to use injection moulded PEEK-OPTIMA™ as an alternative to cobalt chrome in the femoral component of a total knee replacement was investigated in terms of its wear performance. Experimental wear simulation of three cobalt chrome and three PEEK-OPTIMA™ femoral components articulating against all-polyethylene tibial components was carried out under two kinematic conditions: 3 million cycles under intermediate kinematics (maximum anterior-posterior displacement of 5 mm) followed by 3 million cycles under high kinematic conditions (anterior-posterior displacement 10 mm). The wear of the GUR1020 ultra-high-molecular-weight polyethylene tibial components was assessed by gravimetric analysis; for both material combinations under each kinematic condition, the mean wear rates were low, that is, below 5 mm3/million cycles. Specifically, under intermediate kinematic conditions, the wear rate of the ultra-high-molecular-weight polyethylene tibial components was 0.96 ± 2.26 mm3/million cycles and 2.44 ± 0.78 mm3/million cycle against cobalt chrome and PEEK-OPTIMA™ implants, respectively (p = 0.06); under high kinematic conditions, the wear rates were 2.23 ± 1.85 mm3/million cycles and 4.44 ± 2.35 mm3/million cycles, respectively (p = 0.03). Following wear simulation, scratches were apparent on the surface of the PEEK-OPTIMA™ femoral components. The surface topography of the femoral components was assessed using contacting profilometry and showed a statistically significant increase in measured surface roughness of the PEEK-OPTIMA™ femoral components compared to the cobalt chrome implants. However, this did not appear to influence the wear rate, which remained linear over the duration of the study. These preliminary findings showed that PEEK-OPTIMA™ gives promise as an alternative bearing material to cobalt chrome alloy in the femoral component of a total knee replacement with respect to wear performance.

Crosslink Density Is Reduced and Oxidation Is Increased in Retrieved Highly Crosslinked Polyethylene TKA Tibial Inserts

The wear resistance of highly crosslinked polyethylene depends on crosslink density, which may decrease with in vivo loading, leading to more wear and increased oxidation. The relationship among large and complex in vivo mechanical stresses, breakdown of the polyethylene crosslinks, and oxidative degradation is not fully understood in total knee arthroplasty (TKA). We wished to determine whether crosslink density is reduced at the articular surfaces of retrieved tibial inserts in contact areas exposed to in vivo mechanical stress. (1) Does polyethylene crosslink density decrease preferentially in regions of the articular surface of thermally stabilized crosslinked polyethylene tibial components exposed to mechanical stress in vivo; and (2) what is the ramification of decreased crosslink density in TKA in terms of accompanying oxidation of the polyethylene? From May 2011 to January 2014, 90 crosslinked polyethylene tibial components were retrieved during revision surgery as a part of a long-standing implant retrieval program. Forty highly crosslinked polyethylene tibial inserts (27 posterior-stabilized designs and 13 cruciate-retaining designs) retrieved for instability (15 cases), stiffness (11), infection (six), aseptic loosening (four), pain (two), and malposition (two) after a mean time of 18 months were inspected microscopically to identify loaded (burnished) and unloaded (unburnished) regions on the articular surfaces. Swell ratio testing was done according to ASTM F2214 to calculate crosslink density and infrared spectroscopy was used according to ASTM F2102 to measure oxidation. The region of the tibial insert influenced crosslink density. Loaded surface regions had a mean crosslink density of 0.19 (95% confidence interval [CI], 0.18-0.19) mol/dm3, lower than the other three regions (loaded subsurface, unloaded surface, and unloaded subsurface), which had crosslink densities of 0.21 (95% CI, 0.21-0.22; p < 0.01) mol/dm3. Peak oxidation levels were higher in loaded regions with a mean oxidation index (OI) of 0.67 (95% CI, 0.56-0.78) versus unloaded regions with a mean OI of 0.36 (95% CI, 0.27-0.45; p < 0.01). Peak oxidation levels were higher in annealed samples with a mean OI of 0.66 (95% CI, 0.52-0.81) versus remelted samples with a mean OI of 0.40 (95% CI, 0.34-0.47; p < 0.01). The results suggest that the crosslink density decreases and accompanying oxidation is driven predominantly by contact stress conditions. If crosslink density continues to decrease with continued loading over time, crosslinked polyethylene may not provide a clinical advantage over conventional polyethylene in the long term for TKA. Therefore, we will continue to collect longer term retrievals to evaluate mechanical property changes in crosslinked polyethylenes. Although we found a decrease in crosslink density and increase in oxidation in the tibial inserts, the degree of oxidation does not suggest, for now, a reason for concern in these early retrievals. The OI values of the tibial inserts in this study were lower than the critical oxidation level (OI > 3) reported in the literature where polyethylene may lose mechanical properties and have the compromised ability to withstand mechanical loading.

The influence of lubricant temperature on the wear of a metal-free knee implant

Event Abstract Back to Event The influence of lubricant temperature on the wear of a metal-free knee implant Raelene Cowie1*, Adam Briscoe2*, John Fisher1 and Louise M. Jennings1* 1 University of Leeds, Institute of Medical and Biological Engineering, United Kingdom 2 Invibio Biomaterials Solutions, United Kingdom Introduction: PEEK Optima® has been considered for use as an alternative arthroplasty bearing material due to its biocompatibility and favourable material properties[1]. In this study, the wear of all polymer tibial components was assessed articulating against PEEK Optima femoral components under different environmental conditions; experimental wear simulation of conventional metal-on-polyethylene implant materials was carried out in parallel. Materials and Methods: Six size C cruciate retaining PEEK Optima femoral components (Invibio Biomaterials Solutions, UK) and six cobalt chrome femorals of similar initial surface topography and geometry were tested against GUR 1020 all polyethylene tibial components (conventional, EO sterilised) in a 6 station ProSim Knee simulator (Simulation Solutions, UK). N=3 of each material type was tested under room temperature conditions as per standard practice at Leeds and n=3 under elevated temperature conditions where the bulk lubricant temperature was maintained at approximately 33°C by incorporation of a heater system into the simulator. The lubricant used was 25% serum supplemented with 0.03% sodium azide and the simulation was run under Leeds high kinematics[2]. 5 million cycles (MC) of wear simulation was carried out under room temperature and 9MC under elevated temperature. The wear of the UHMWPE tibials was assessed by their loss in mass by gravimetric analysis with unloaded soak controls used to compensate for moisture uptake. Statistical analysis was carried out using ANOVA with significance taken at p<0.05 Results: Figure 1 shows the wear of the UHMWPE tibials under the different test conditions. At room temperature, the wear of the UHMWPE tibial was similar against the different femoral materials (p>0.05). Under elevated temperature conditions, the wear rate of UHMWPE was lower than at room temperature for both femoral materials. A high density of light scratches was observed on all the PEEK Optima implants but this did not influence the wear rate which remained constant over the duration of the study. Discussion: The study shows a similar rate of wear of UHMWPE tibials against PEEK Optima and cobalt chrome femorals of similar initial geometry and surface topography independent of the temperature of the bulk lubricant. Testing at an elevated temperature reduced the wear of the UHMWPE against both femoral materials, which may be attributed to deposition of protein from the lubricant onto the articulating surfaces artificially protecting the implants. Conclusion: This study shows that PEEK Optima has the potential for use as a metal-free knee and that testing under elevated lubricant temperature conditions may have introduced a test artefact which would not occur under room temperature conditions or in vivo. Invibio Biomaterials Solutions Ltd. provided funding and materials for this study.

A 3D finite element model to investigate prosthetic interface stresses of different posterior tibial slope.

Posterior tibial slope that is created during proximal tibial resection in total knee arthroplasty has emerged as an important factor in the mechanics of the knee joint and the surgical outcome. But the ideal degree of posterior tibial slope for recovery of the knee joint function and preventions of complications remains controversial and should vary in different racial groups. The objective of this paper is to investigate the effects of posterior tibial slope on contact stresses in the tibial polyethylene component of total knee prostheses. Three-dimensional finite element analysis was used to calculate contact stresses in tibial polyethylene component of total knee prostheses subjected to a compressive load. The 3D finite element model of total knee prosthesis was constructed from the images produced by 3D scanning technology. Stresses in tibial polyethylene component were calculated with four different posterior tibial slopes (0°, 3°, 6° and 9°). The 3D finite element model of total knee prosthesis we presented was well validated. We found that the stress distribution in the polythene as evaluated by the distributions of the von Mises stress, the maximum principle stress, the minimum principle stress and the Cpress were more uniform with 3° and 6° posterior tibial slopes than with 0° and 9° posterior tibial slopes. Moreover, the peaks of the above stresses and trends of changes with increasing degree of knee flexion were more ideal with 3° and 6° posterior slopes. The results suggested that the tibial component inclination might be favourable to 7°-10° so far as the stress distribution is concerned. The range of the tibial component inclination also can decrease the wear of polyethylene. Chinese posterior tibial slope is bigger than in the West, and the current domestic use of prostheses is imported from the West, so their demands to tilt back bone cutting can lead to shorten the service life of prostheses; this experiment result is of important clinical significance, guiding orthopaedic surgeon after the best angle to cut bone.

Control of Lay on Cobalt Chromium Alloy Finished Surfaces Using Magnetic Abrasive Finishing and Its Effect on Wettability

Freeform surfaces, including the femoral components of knee prosthetics, present a significant challenge in manufacturing. The finishing process is often performed manually, which leads to surface finish variations. In the case of knee prosthetics, this can be a factor leading to accelerated wear of the polyethylene tibial component. The wear resistance of polyethylene components might be influenced by not only the roughness but also the lay of femoral component surfaces. This study applies magnetic abrasive finishing (MAF) for nanometer-scale finishing of cobalt chromium alloys, which are commonly used in knee prosthetics and other freeform components. Using flat disks as workpieces, this paper shows the dominant parameters for controlling the lay in MAF and demonstrates the feasibility of MAF to alter the lay while controlling the surface roughness. The manually finished disk surfaces (with roughness around 3 nm Sa), consisting of random cutting marks, were compared to MAF-produced surfaces (also with roughness around 3 nm Sa) with different lays. Tests using deionized water droplets show that the lay influences the wetting properties even if the surface roughness changes by no more than a nanometer. Surfaces with unidirectional cutting marks exhibit the least wettability, and increasing the cross-hatch angle in the MAF-produced surfaces increases the wettability. Surfaces consisting of short, intermittent cutting marks were the most wettable by deionized water.