Polyethylene Failure Research Articles

Polyethylene Failure of the Patellar Component in New Jersey Low-Contact Stress Total Knee Arthroplasties

In a postoperative 5- to 12-year follow-up study of 598 New Jersey low-contact stress total knee arthroplasties, 32 required revision. All retrieved patellar components were examined for polyethylene damage. These 32 cases had 3 types of failure: split rupture (7 cases), peripheral wear (21), and cantilevering breakage (4), respectively 75%, 64.3%, and 100% of which showed subluxation and/or tilting of the patellar component on the prerevision roentgenograms. Misalignment at the joint contact surfaces and rotational blockage of the mobile patellar component were considered the major causes of the failure. A design of a flatter metallic button (giving larger focal thickness of the polyethylene) and a dome-shaped polyethylene (reducing stress concentration at the pinnacle) may alleviate the failure driving mechanism should subluxation or tilting of the patellar component take place.

Revision of a Charité artificial disc 9.5 years in vivo to a new Charité artificial disc: case report and explant analysis

This report describes a case of one-level total disc replacement (TDR) of L5-S1 requiring revision at 9.5 years following the index surgery due to polyethylene failure caused by high oxidation. Primary revision strategies for TDR include instrumented posterolateral fusion, or 360 degrees fusion with replacement of the prosthesis with cages or allograft bone. A revision of a TDR with a similar prosthesis has not been described in the literature. An active 42-year-old female underwent TDR with a Charité artificial disc. She remained active and pain free for 9.5 years before presenting with moderate low-back pain and sciatica. Radiographic studies confirmed a fragmented polyethylene core. The failed prosthesis was revised to a new Charité disc with the patient again active and pain free for 6 months following surgery. Chemical and physical analysis of the core indicated high oxidation due to gamma sterilization in air; a process changed to gamma sterilization in nitrogen in 1998 to meet industry standards. No evidence of wear debris was noted. Revision of an artificial disc with an artificial disc can be performed safely and adequately with the Charité disc prosthesis as an alternative to fusion necessitated by a device failure. An anterior revision approach carries significant risk and should only be performed by surgeons experienced in anterior lumbar surgery.

Challenges in total ankle arthroplasty.

In the past, total ankle arthroplasty was largely abandoned due to poor survivorship most often caused by loss of bone support. High complication rates were also reported. Despite this, there is renewed interest in ankle arthroplasty and encouraging results are seen in survivorship with midterm follow-up. The procedure, however, remains more challenging than total hip or total knee arthroplasty. With the limited soft tissue envelope, wound problems are not uncommon. Forces at the ankle are very large and yet the surface area for prosthetic support is small. Therefore, fixation can be more difficult. The strongest bone can be eccentric at the distal tibia. The tibial prosthesis can, therefore, tend to settle into the softer bone often laterally. Polyethylene needs to be sufficiently thick to maintain its integrity but that requires a larger bone resection, which weakens bone support. Polyethylene failure or wear leads to the majority of failures in hip and knee arthroplasty. There is a need for further basic science research in total ankle arthroplasty. The lessons learned from other arthroplasty should be considered in ankle arthroplasty design.

Long-Term Results of Low Contact Stress Mobile-Bearing Total Knee Replacements

Five hundred ninety-eight consecutive primary low contact stress total knee replacements were done in 502 patients between 1985 and 1990. Clinical review was available for 495 knees (406 patients), 228 knees with meniscal-bearing prostheses and 267 knees with rotating-platform prostheses. The average followup was 12 years (range, 10-15 years). The average postoperative knee and functional scores were 87 points and 75 points, respectively. The average postoperative range of motion was 110 degrees. Fifty-six knees (11%) required revision for excessive wear of the tibial insert (41), dislocation (10), patellar polyethylene breakage (one), component loosening (one patellar, one tibial), and infection (two). During revision, osteolysis (20 knees), patellar polyethylene failure (33), and femoral component fracture (one) were seen. The overall survivorship was 88.1% at 15 years using Kaplan-Meier analysis. The survival rate was 83% for the meniscal-bearing prostheses and 92.1% for the rotating-platform prostheses. The Low Contact Stress mobile-bearing knee prosthesis has no superiority over that of fixed-bearing knees, especially for the meniscal-bearing design in prevention of polyethylene failure or revision. Based on the results of this study, the use of the LCS meniscal-bearing prosthesis does not appear to be justified.

Revision of well-fixed cementless acetabular components for polyethylene failure.

The results of revision of well-fixed Porous Coated Anatomic cementless acetabular components for polyethylene failure or periacetabular osteolysis in 18 hips (14 patients) are reported. Revisions were done with larger diameter cementless acetabular components replacing one-piece Porous Coated Anatomic devices for which no replacement liner was available. The objective was to determine the increase in size of the revision acetabular component and to assess clinical and radiographic outcomes. The Porous Coated Anatomic components were in place for an average of 7.8 years. At an average followup of 68 months, all revision components remain in place. Preoperatively, 12 hips in 10 patients had radiographic osteolysis, and 25 osteolytic lesions in 17 patients were grafted at revision. All grafted lesions showed partial or complete evidence of bone graft consolidation. The average revision component size increased 8.5 mm in diameter (range, 3-14 mm) compared with the primary component size. This corresponded to an average 6.5-mm increase in the acetabular cavitary diameter. When locking mechanism failure in a well-fixed cementless acetabular component prevents polyethylene liner replacement, acetabular component revision can provide good clinical and radiographic results with acceptable bone loss and improved access to osteolytic areas for debridement and grafting.

Polyethylene damage on the nonarticular surface of modular total knee prostheses.

Modular tibial implants submitted for retrieval analysis were examined for evidence of cold flow, wear, or polyethylene failure. All retrieved components showed areas of cold flow and wear. Significant damage, defined as pitting, gouging, or delamination was observed in 77% of the retrieved implants. Cold flow deformation commonly was observed at the junction of the polyethylene and locking mechanisms or junction of the polyethylene and the edge of the tibial tray. Control implants did not show such areas of damage. Clinical factors such as age, activity status, length of implantation, limb alignment before revision, and thickness of the tibial insert did not correlate with backside wear. No association was found between polyethylene thickness, time of implantation, limb or prosthesis alignment, or activity status or weight of the patient.

Subtrochanteric shortening and derotational osteotomy in primary total hip arthroplasty for patients with severe hip dysplasia: 5-year follow-up

Twenty-one primary hip arthroplasties were performed in Crowe grade 3 or 4 hip dysplasia using a subtrochanteric shortening osteotomy. Average patient age was 48.2 years. Average follow-up was 5.8 years (minimum, 2 years). Femoral fixation was cemented in 10 hips and uncemented in 11 hips. All acetabular components were uncemented, with 33% requiring structural autograft. Ninety-one percent of femoral osteotomies healed without complication. Two osteotomy nonunions required revision. Two acetabular revisions were performed for malposition and polyethylene failure. Three patients experienced postoperative dislocation. One cemented femoral component was revised for loosening. However, no neurologic deficiencies were identified. Harris hip score improved from 32.5 to 73.6. Limp improved in 60% of patients and dependence on assistive walking device improved in 40% of patients. Subtrochanteric shortening osteotomy is a safe and predictable method of restoring the anatomic hip center in high developmental hip dislocation. However, the complication rate in these patients is higher than primary hip arthroplasty for osteoarthritis. © 2003 Elsevier Inc. All rights reserved.

Posterior femoral impingement causing polyethylene failure in total knee arthoplasty

Several reports in the literature describe dislocation and fractures of the meniscal bearings as a result of polyethylene failure after total knee arthroplasty. In this case of an asymptomatic patient with a clinically uneventful 7-year follow-up, who died a year later of an unrelated cause, we found impressive damage of the polyethylene components. This damage, at the posterior corner of the meniscal bearing elements, was caused by regrowth of the posterior femoral osteophytes. The primary osteophytes had been resected adequately during the arthroplasty. These osteophytes are related to a bone–polyethylene impingement that occurs at >110° of knee flexion. The possible range of motion of an artificial joint, owing to its design, is less than the range of flexion sometimes reached clinically by the patient. This is a problem that should be solved by the industry in the near future. Copyright 2002, Elsevier Science (USA). All rights reserved.

The clinical history and development of the low contact stress total knee arthroplasty.

Contemporary total knee arthroplasty (TKA) has evolved over the past 30 years as a result of early prosthetic design failure. Hinge-type implants demonstrated a high loosening rate because of overconstraint. Curved-on-flat prostheses, which were popular in the late 1970s, became associated with a high incidence of polyethylene failure. The Low Contact Stress (LCS) Total Knee System (DePuy Orthopaedics Inc, Warsaw, Ind), a mobile-bearing knee arthroplasty design, was introduced in 1977. The LCS Total Knee System, now in its 25th year without alterations in articular geometry, has demonstrated clinical success and has had an impact on evolving prosthetic designs. Introduced in 2001, the LCS Complete Total Knee System provides further refinements in patient fit without changing the fundamental design principles. Surgeons are cautioned to use a well-proven clinical design, as biomechanical variations critically impact clinical outcomes.

Gamma irradiation alters fatigue-crack behavior and fracture toughness in 1900H and GUR 1050 UHMWPE.

Pitting and delamination remain causative factors of polyethylene failure in total knee replacement. Gamma irradiation induces cross linking in ultra-high-molecular-weight polyethylene, which has been shown to improve wear resistance. Irradiation may reduce fracture toughness and fatigue strength, however, and the effects of irradiation are dependent upon the resin, processing technique, and radiation dose. The effects of varying levels of gamma irradiation (0, 33, 66, and 100 kGy) on the fracture toughness and fatigue-crack resistance of UHMWPE, isostatically molded from 1900H and GUR 1050 resins, were examined. Paris law regressions were performed to quantify fatigue-crack propagation rates as functions of change in stress intensity, and J-integral methods were used to quantify the elastic-plastic fracture toughness. The results indicated that gamma irradiation reduced the resistance of both materials to fatigue-crack growth, and that the reductions were radiation dosage and resin dependent. Irradiation at any level was detrimental to the fracture toughness of the 1900H specimens. Irradiation at 33 kGy increased fracture toughness for the GUR 1050 specimens, and substantial reductions were observed only at the highest irradiation level. Scanning electron microscopy of the fracture surface revealed diamond-like fracture patterns of the nonirradiated specimens indicative of ductile, multilevel fracture. Pronounced striations were apparent on these fracture surfaces, oriented perpendicular to the direction of crack growth. The striations appeared as folds in surface layers of the GUR 1050 specimens. At the highest irradiation levels, the striations were nearly eliminated on the fracture surfaces of the 1900H specimens, and were markedly less severe for the GUR 1050. These results demonstrated that at higher irradiation levels the materials became more brittle in fatigue, with less ductile folding and tearing of the fracture surfaces.

The AGC total knee prosthesis at average 11 years

A retrospective study of a series of 126 consecutive primary cemented total knee replacements using the AGC prosthesis is reported. Sixty-two knees were available for long-term review with an average clinical follow-up of 11.4 years (range, 8.4-13.6 years). The survivorship was 95%, defining the endpoint as revision of all components for any reason except sepsis. The average knee flexion was 110.9°. The average Knee Society score was 91, and the average Knee Society Functional score was 67. There was no finding of tibial polyethylene failure, wear debris-generated osteolysis, or tibial or femoral loosening. Seven metal-backed patellae developed wear-through at an average of 80.4 months (7 of 126 for a 5.5% failure rate), with 3 (2.3%) resulting in complete revision. The authors continue to use the AGC prosthesis with an all-polyethylene patella. Compared with historical controls, the AGC has comparable survivorship.

Craze morphology and molecular orientation in the slow crack growth failure of polyethylene

An optical microscopy study and a micro-Raman spectroscopy study were carried out on polyethylene samples subjected to an environmental stress crack resistance (ESCR) test. The aim was to elucidate the molecular deformation mechanisms associated with the failure process. It has been shown that in the early stages of the ESCR test, in a regime of low local stress, failure in the craze occurs via a brittle process with limited ductility and with molecular orientation being detected. As the experiment progresses, however, extensive fibrillation takes place. The molecular orientation in these fibrils was found to be comparable to that measured in cold-drawn samples. Moreover, the fibril molecular orientation decreased from the crack to craze tip and was found to be higher in the midrib part of the fibril (fibril failure point). As a consequence, fibril creep is the most likely mechanism of failure in the craze. Microscopy and Raman measurements showed that the extent of the brittle process is molecular weight-dependent, that is, the brittle process seems to operate longer at higher molecular weights. These observations are in agreement with a previous work which showed that the molecular stress per macroscopic strain/stress decreases with increasing molecular weight, therefore holding the high molecular weight craze in a regime of low local stress for longer testing times. Fibrils spanning the craze are envisaged as the anchor points that hold the structure during the process of failure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 283–296, 2000

An improved method for measuring tibiofemoral contact areas in total knee arthroplasty: a comparison of K-scan sensor and Fuji film

A computerised, real time, thin-film pressure transducer method is used to measure tibiofemoral contact area in total knee arthroplasty (TKA) devices that is easier and more reliable and reproducible as compared to the Fuji pressure-sensitive film technique. Many authors have suggested that contact areas and pressures within TKA devices can be a predictor of wear and failure of the ultra-high molecular weight polyethylene (UHMWPE) tibial insert. In this study, two contact area measurement techniques (Fuji pressure-sensitive Film and K-scan sensor system) were compared using a custom TKA testing jig designed for freedom of movement so that in any loading configuration the component found and seated in its own “home” position. The K-scan system was used to measure contact areas of one TKA design at several angles from 0 to 110° flexion with loads equating to 4, 4.5, and 5 times body weight. For comparison, four ranges of Fuji film were used to measure areas at the same flexion angles but at 5 times body weight only. Contact areas measured with the Fuji films were 11–36% (p<0.05) lower than those measured by the K-scan sensor.

Development of an extremely wear-resistant ultra high molecular weight polyethylene for total hip replacements.

Osteolysis induced by ultra high molecular weight polyethylene wear debris is one of the primary factors limiting the lifespan of total hip replacements. Crosslinking polyethylene is known to improve its wear resistance in certain industrial applications, and crosslinked polyethylene acetabular cups have shown improved wear resistance in two clinical studies. In the present study, crosslinked polyethylene cups were produced by two methods. Chemically crosslinked cups were produced by mixing a peroxide with ultra high molecular weight polyethylene powder and then molding the cups directly to shape. Radiation-crosslinked cups were produced by exposing conventional extruded ultra high molecular weight polyethylene bar stock to gamma radiation at various doses from 3.3 to 100 Mrad (1 Mrad = 10 kGy), remelting the bars to extinguish residual free radicals (i.e., to minimize long-term oxidation), and then machining the cups by conventional techniques. In hip-joint simulator tests lasting as long as 5 million cycles, both types of cross-linked cups exhibited dramatically improved resistance to wear. Artificial aging of the cups by heating for 30 days in air at 80 degrees C induced oxidation of the chemically crosslinked cups. However, a chemically crosslinked cup that was aged 2.7 years at room temperature had very little oxidation. Thus, whether substantial oxidation of chemically crosslinked polyethylene would occur at body temperature remains unclear. The radiation-crosslinked remelted cups exhibited excellent resistance to oxidation. Because crosslinking can reduce the ultimate tensile strength, fatigue strength, and elongation to failure of ultra high molecular weight polyethylene, the optimal crosslinking dose provides a balance between these physical properties and the wear resistance of the implant and might substantially reduce the incidence of wear-induced osteolysis with total hip replacements.

Analysis of ultrahigh molecular weight polyethylene failure in artificial knee joints: Thermal effect on long-term performance

The mechanism resulting in damage to and failure of ultrahigh molecular weight polyethylene (UHMWPE) tibial inserts was investigated on clinically retrieved components. The severity of the subsurface damage increased with the length of time that the component had been implanted. A theoretical analysis was developed to account for the generation of subsurface damage based on a heat transfer model. Friction generates surface heat during articulation of total knee systems. Due to the cooling effect of body fluid on the surface, the rise in temperature on the UHMWPE surface is lower than that below the surface. The peak temperature was estimated to occur on a plane positioned about 1 to 2 mm below the surface. This result was similar to the bulk temperature variation observed during in vivo and in vitro studies by other investigators. Although the difference in temperature on and below the surface is only a few degrees, the thermal effect becomes apparent after a long time and may be explained by the viscoelastic behavior of polymers: the temperature–time equivalence. It is therefore suggested that this thermal effect is another contributory factor to material damage, in addition to high stress and oxidative degradation (in appropriate cases). Therefore, any technological efforts aimed at improving the performance of artificial joint prostheses should minimize the thermal effects at the subsurface of the articular components. © 1999 John Wiley & Sons, Inc. J Biomed Mater Res (Appl Biomater) 48: 159–164, 1999

Analysis of ultrahigh molecular weight polyethylene failure in artificial knee joints: thermal effect on long-term performance.

The mechanism resulting in damage to and failure of ultrahigh molecular weight polyethylene (UHMWPE) tibial inserts was investigated on clinically retrieved components. The severity of the subsurface damage increased with the length of time that the component had been implanted. A theoretical analysis was developed to account for the generation of subsurface damage based on a heat transfer model. Friction generates surface heat during articulation of total knee systems. Due to the cooling effect of body fluid on the surface, the rise in temperature on the UHMWPE surface is lower than that below the surface. The peak temperature was estimated to occur on a plane positioned about 1 to 2 mm below the surface. This result was similar to the bulk temperature variation observed during in vivo and in vitro studies by other investigators. Although the difference in temperature on and below the surface is only a few degrees, the thermal effect becomes apparent after a long time and may be explained by the viscoelastic behavior of polymers: the temperature-time equivalence. It is therefore suggested that this thermal effect is another contributory factor to material damage, in addition to high stress and oxidative degradation (in appropriate cases). Therefore, any technological efforts aimed at improving the performance of artificial joint prostheses should minimize the thermal effects at the subsurface of the articular components.

Intraoperative assessment of tibiofemoral contact stresses in total knee arthroplasty

The production of polyethylene wear debris in total knee arthroplasty (TKA) is due to multiple factors. In particular, inadequate implant alignment and high bearing surface contact stresses are associated with polyethylene failure. Optimal implant placement and soft tissue balancing may contribute to reducing wear and the production of polyethylene particles. We present a case in which a quantitative technique was used to measure tibiofemoral contact stresses during implantation of a total knee prosthesis in vivo. In a knee with preoperative varus and fixed flexion deformity, medial compartment contact stresses after initial resection were reduced from 14.3 MPa to 11.3 MPa in neutral alignment by additional bone resection. Posterior cruciate release was required to reduce contact stresses further and to provide satisfactory balance between medial and lateral compartments, as determined by the operating surgeon, and was confirmed by the measurement system (3.8 MPa medially; 3.0 MPa laterally). This technique has potential to fine-tune implant positioning and ligament balancing during TKA.

The incidence of modular tibial polyethylene insert exchange in total knee arthroplasty when polyethylene failure occurs

One of the primary reasons for utilizing modular tibial polyethylene inserts (MTPI) at the time of total knee arthroplasty is to have the ability to simply exchange the polyethylene at the time of revision surgery when polyethylene failure has occurred. During a 2-year period from January 1993 to December 1994, 62 revision total knee arthroplasties were reviewed from five different institutions in North America, which were performed secondary to modular tibial insert failure. In 55 cases (88.7%), significant scoring and/or damage to the femoral and/or tibial components occurred necessitating revision of one or both components. This series does not support the premise that polyethylene exchange is common at the time of revision surgery for MTPI failure. Of the patients 88.7% had MTPI failure resulted in femoral and/or tibial component revision secondary to surface damage to the femoral component and/or tibial component baseplate. In order to avoid femoral and tibial component wear secondary to MTPI failure, early recognition is necessary to allow the much simpler operation consisting of polyethylene liner exchange only.

Polyethylene failure in New Jersey low-contact stress total knee arthroplasty.

From January 1985 to December 1990, 598 consecutive New Jersey low-contact stress (LCS) total knee arthroplasties (TKAs) were performed for gonarthrosis. Among these 598 operations, 322 were with rotating platform elements and 276 were with meniscal bearing elements. During 5 to 8 years of follow-up, eight knees had severe symptomatic polyethylene failure that required revision surgery; all eight cases were meniscal bearing types. The failed polyethylene inserts were retrieved and studied. It was observed that there were four probable failure mechanisms associated with the catastrophic polyethylene wear. First, insufficient thickness of the meniscal bearing was the major reason for wear. Second, the malpositioning of the metal tibial tray in the transverse plane resulted in the breaking of the meniscal bearing. Third, the inability of the patellar to rotate due to tissue ingrowth made the polyethylene break. Last, yellowing of the subsurface of the meniscal bearing was a sign of polyethylene failure. These four possible failure mechanisms are all associated with the design of the meniscal bearing type of LCS knee prostheses. Therefore, it is suggested that the design of the LCS knee prosthesis should be modified.

Fatigue performance of ultra-high-molecular-weight polyethylene: effect of gamma radiation sterilization

Ultra-high-molecular-weight polyethylene (UHMWPE) failure presents a significant materials concern in the orthopaedic community. Clinical failure following joint arthroplasty can result from the biological response to wear debris as well as structural failure owing to UHMWPE fatigue. In this study, cantilever rotating beam fatigue testing was conducted on GUR 415 UHMWPE in both the unsterilized and gamma radiation sterilized conditions. Calculations of flexural fatigue stresses were based on extreme fibre stresses and assumed negligible plastic deformation. Both material conditions exhibited similar fatigue strengths at 250,000 cycles (approximately 41 MPa) and at one million cycles (approximately 36 MPa), but a large difference developed after two million cycles. At ten million cycles, the unsterilized condition exhibited a fatigue strength of approximately 31 MPa, while the gamma-sterilized condition exhibited a reduced fatigue strength of approximately 18 MPa, an approximate decrease of 42%. High-cycle fatigue testing was necessary to fully characterize this behaviour owing to the pronounced difference in fatigue behaviour beyond two million cycles. These results suggest that gamma radiation sterilization of UHMWPE medical implants reduces their resistance to cyclic loading and, subsequently, may contribute to the associated fatigue-related failures which have been reported clinically.