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PubMed1990

Cementless uncoated polyethylene acetabular components in total hip replacement. Review of five- to 10-year results.

We reviewed the results of 545 consecutive total hip replacements using a cementless non-coated high-density polyethylene acetabular component combined with a cemented Müller stem at five to 10 years. In all, 421 patients (445 hips) were available for review, 118 by questionnaire and 303 by examination and radiography. Of these, 86% had a good or excellent result. We found a high rate of radiological loosening of the cup after the sixth year, and a high rate of clinical loosening after the eighth year. Loosening was commoner in women, in younger patients and where a smaller size of acetabulum had been used. Calcar resorption was significantly related to loosening of the acetabulum. Loosening appeared to be mainly due to polyethylene debris produced by micro-movement of the acetabulum against the bone, which had resulted in a giant cell foreign body reaction and subsequent bone erosion. We have abandoned the use of this prosthesis and suggest that direct contact between bone and polyethylene should be prevented by a coating of metal or some other material.

Acetabulum↗
PubMed1997

Ceramic-ceramic and metal-polyethylene total hip replacements: comparison of pseudomembranes after loosening.

We made a semiquantitative study of the comparative histology of pseudomembranes from 12 loose cemented ceramic-ceramic and 18 metal-polyethylene total hip replacements. We found no significant difference in cellular reaction between the two groups, but there was a major difference in the origin of the particulate debris. In the metal-polyethylene group, polyethylene of articular origin was predominant, while in the ceramic-ceramic group the cellular reaction appeared to be a response to zirconia ceramic particles used to opacify cement used for fixation. Isolation and characterisation of the debris showed that the zirconia particles formed the greatest proportion (76%) in ceramic-ceramic hips, while alumina debris of articular origin formed only 12%. Our study has indicated that aseptic loosening of ceramic cups is not due to a response to debris generated at the articular interface, but to mechanical factors which lead to fragmentation of the cement.

Bone Cements↗
PubMed1997

Measurement of polyethylene wear in cementless total hip arthroplasty.

We made a clinical study of polyethylene wear in 240 hips of 187 patients having primary total hip arthroplasties from 1989 to 1990, using uncemented Osteonics components, with a head size of 26 mm. We excluded cups with anteversion of over 20 degrees and measured linear wear by a new method using a digitiser and special software of our design. Follow-up was from two to five years (mean 4.3). The mean age at operation was 50.3 years, with more men than women (1.4:1). The mean linear wear per year was 0.15 mm; this did not increase with the longevity of the prosthesis (p = 0.54). In 59 hips showing evidence of osteolysis, the mean linear wear rate was significantly higher at 0.23 mm/year (p <0.001). The mean linear wear rate also correlated significantly with age at the time of operation (p = 0.008), but we found no significant correlations with body-weight, gender, aetiology of the disease, thickness of polyethylene, or cup position. Our new method of measurement is time-saving and reproducible. The results confirm the greater rate of linear wear of polyethylene in patients showing osteolysis and in those who are younger.

Adult↗
PubMed1997

Number of polyethylene particles and osteolysis in total joint replacements. A quantitative study using a tissue-digestion method.

Our aim was to analyse the influence of the size, shape and number of particles on the pathogenesis of osteolysis. We obtained peri-implant tissues from 18 patients having revision surgery for aseptically loosened Freeman total knee replacements (10), Charnley total hip replacements (3) and Imperial College/London Hospital double-cup surface hip replacements (5). The size and shape of the polyethylene particles were characterised using SEM and their concentration was calculated. The results were analysed with reference to the presence of radiological osteolysis. The concentration of polyethylene particles in 6 areas with osteolysis was significantly higher than that in 12 areas without osteolysis. There were no significant differences between the size and shape of the particles in these two groups. We conclude that the most critical factor in the pathogenesis of osteolysis is the concentration of polyethylene particles accumulated in the tissue.

Chromatography, High Pressure Liquid↗
PubMed1999

The influence of weight-bearing on the measurement of polyethylene wear in THA.

We have studied the influence of weight-bearing on the measurement of wear of the polyethylene acetabular component in total hip arthroplasty using two techniques. The measured vertical wear was significantly greater when radiographs were taken weight-bearing rather than with the patient supine (p = 0.001, method 1; p = 0.007, method 2). Calculations of rates of linear wear of the acetabular component were significantly underestimated (p < 0.05) when radiographs were taken supine. There are two reasons for this. First, a change in pelvic orientation when bearing weight ensures that the thinnest polyethylene is brought into relief, and secondly, the head of the femoral component assumes the position of maximal displacement along its wear path. Interpretation of previous studies on both linear and volumetric polyethylene wear in total hip arthroplasty should be reassessed in the light of these findings.

Acetabulum↗
PubMed1999

Polyethylene wear, osteolysis and acetabular loosening with an HA-coated hip prosthesis. A follow-up of 94 consecutive arthroplasties.

We have followed up for a period of seven to nine years 100 consecutive arthroplasties of the hip in which an entirely HA-coated implant had been used. The clinical results were excellent and bony incorporation was extensive in all components. No stem became loose or subsided but five cups were revised because of loosening after 3.8 to 5.5 years, having functioned painlessly and shown radiological ingrowth. Revision procedures because of excessive polyethylene wear have been performed on 18 hips and are planned for six more. Two eroded metal backings with worn-through polyethylene were exchanged; six hips showed metallosis without polyethylene wear-through. There were two cases of granulomatous cysts in the groin and 66 hips had osteolysis located periarticularly, in the greater trochanter or in the acetabulum.

Acetabulum↗
PubMed2001

A comparison of polyethylene wear in hips with cobalt-chrome or zirconia heads. A prospective, randomised study.

We have reviewed 70 patients with bilateral simultaneous total hip arthroplasties to determine the rate of failure and to compare polyethylene wear and osteolysis between an implant with a cobalt-chrome head and Hylamer liner with that of a zirconia head and Hylamer liner. The mean thickness of the polyethylene liner was 11.0 mm (8.8 to 12.2) in the hip with a zirconia head and 10.7 mm (8.8 to 12.2) in that with a cobalt-chrome head. At follow-up at 6.4 years no acetabular or femoral component had been revised for aseptic loosening and no acetabular or femoral component was loose according to radiological criteria in both the cemented and cementless groups. The mean rate of linear wear and annual wear rate were highest in the 22 mm zirconia femoral head (1.25 mm (SD 1.05) and 0.21 mm (SD 0.18), respectively) and lowest in the 22 mm cobalt-chrome femoral head (0.70 mm (SD 0.39) and 0.12 mm (SD 0.07), respectively). The mean volumetric wear was highest in the 28 mm zirconia femoral head (730.79 mm ) and lowest in the 22 mm cobalt-chrome femoral head (264.67 mm3), but if the results were compared by size of the femoral head and type of material there was no statistical difference (p > 0.05). Sequential measurements of annual wear showed that the zirconia femoral head had a relatively higher rate of penetration than the cobalt-chrome head over the first three years; thereafter the rate of wear was reduced and compared favourably with that of cobalt-chrome heads. There was a statistically significant relationship between the wear of the polyethylene liner and the age of the patient, male gender and the degree of abduction angle of the cup, but not diagnosis, weight, hip score, range of movement, or amount of anteversion. Osteolysis was identified on both sides of the acetabulum in six patients (9%). Of 12 hips with acetabular osteolysis, six had a 28 mm cobalt-chrome femoral head and the remaining six a 28 mm zirconia head. Osteolysis was observed in zones 1A and 7A of the femur in two hips (3%) with a 28 mm zirconia head (cemented hip) and in four (6%) with a 28 mm cobalt-chrome femoral head (cementless hip). Our findings suggest that although the performance of a zirconia femoral head with a Hylamer liner was not statistically different from that of a cobalt-chrome femoral head and Hylamer liner, there was a trend for the zirconia head to be worse than the cobalt-chrome femoral head.

Adult↗
PubMed2005

The use of cementless expansion acetabular component and an alumina-polyethylene bearing in total hip arthroplasty for osteonecrosis.

We performed 114 consecutive primary total hip arthroplasties with a cementless expansion acetabular component in 101 patients for advanced osteonecrosis of the femoral head. The mean age of the patients at surgery was 51 years (36 to 62) and the mean length of follow-up was 110 months (84 to 129). The mean pre-operative Harris hip score of 47 points improved to 93 points at final follow-up. The polyethylene liner was exchanged in two hips during this period and one broken acetabular component was revised. The mean linear wear rate of polyethylene was 0.07 mm/year and peri-acetabular osteolysis was seen in two hips (1.9%). Kaplan-Meier analysis indicated that the survival of the acetabular component without revision was 97.8% (95% confidence interval 0.956 to 1.000) at ten years. Our study has shown that the results of THA with a cementless expansion acetabular component and an alumina-polyethylene bearing surface are good.

Acetabulum↗
PubMed1993

[UHMW-polyethylene as the substance for articulating components of joint prostheses].

In recent years there has been an increase in the incidence of problems with UHMWPE used in implants. In particular the risk of osteolysis and loosening resulting from the body's reactions to polyethylene wear particles must be eliminated. A variety of investigations with UHMWPE provided hints on how to improve the quality of the original material, machining and reduction of contaminants, which have since been implemented. The knowledge gained of the visco-elastic behaviour of this polymer makes it possible to optimize the design of implant components. The need to sterilize the component parts with ionizing radiation results in changes in the structure of UHMWPE. Via oxidation and acceleration of the ageing process of the material, irradiation in air reduces the molecular weight, which is important for the tribological properties. The use of a nitrogen atmosphere during irradiation and for storage makes it possible to take advantage of the positive effects of this method of sterilization via cross-linking of the polyethylene. Positive ductile properties are thus maintained and the resistance to wear is increased. An investigation of 134 components explanted during re-operation revealed a wide scatter in the results of wear. One of the reasons for increased polyethylene wear is the additional abrasive effect of particles of bone cement that get into the space between the articulating components; this can be minimized by a meticulous cementing technique.

Aged↗
PubMed1998

[Polyethylene in total endoprosthetics--a dead end for permanent implants?].

Faced with a growing number of younger patients in need of total joint arthroplasty, orthopaedic surgeons are demanding long-term implants for total joint replacement. An assessment of the long-term mechanical behaviour is vivo of all biomaterials in common use in prostheses is in progress. In the present paper, we discuss the long-term reliability of polyethylene (UHMWPE) in joint replacement in terms of tribology and the different biomechanical situation in various human joints. Long-term failure mechanisms for polyethylene in total hip arthoplasty (THA) differ from those seen in total knee arthroplasty (TKA) although the same materials are used. It is thus questionable whether improvements in wear rates of polyethylene in THA would be helpful in TKA.

Biomechanical Phenomena↗
PubMed1999

[An optical method for determining deformation and form changes in polyethylene surfaces of explanted acetabular cups of hip endoprostheses].

AIM: Most methods used for the determination of volumetric wear of polyethylene cups are based on the assumption that the head of the prosthesis penetrates the cup in "cylindrical" fashion. The new accurate optical method is independent of this disputable assumption. METHOD: The articulating surface of the cup is scanned with light and a data set of 60,000 pixels obtained in this way is stored in a computer. Data obtained from used cups were compared with those obtained from unused cups. The volumetric wear was calculated directly by threefold integration. To assess the changes in surface shape, the data are fitted by an ellipsoid whose long axis defines the mean direction of load. A total of 18 retrieved and 3 unused cups of different types were studied. RESULTS: The unused acetabular cups deviated only slightly from ideal hemispheres. The surfaces showed rotational symmetry, and an undulation having an amplitude of 0.1 mm between dome and equator. For all explanted cups, the assumption of cylindrical penetration of the head into the polyethylene was shown not to represent the true situation. The cup expands in all directions, and the volumetric wear is underestimated by 50% with the traditional methods. The data suggest that long-term survival may be jeopardized when the main direction of loading is centered on the dome of the cup. Ceramic heads were associated with smaller rates of volumetric wear. CONCLUSION: The new optical method is characterised by short measuring times, precision and simple application. Analysis of the wear patterns of polyethylene components using this technique may contribute to a further understanding of the complex mechanisms of aseptic loosening.

Acetabulum↗
PubMed2001

[Stretched polyethylene (UHMWPE)--a new substance modification for minimizing wear in artificial knee joint replacement].

Polyethylene wear is a major cause of aseptic loosening of knee endoprostheses. With the aim of minimizing this mechanical wear, we stretch-modified the structure of polyethylene. From plates of UHMWPE, stretched PE samples were produced under defined conditions, and subsequently submitted to friction tests in a fluid environment (cycles 5 x 10(5), frequency 1.5 Hz, load 500 N, contact stress 10 MPa). After load testing, the stretched samples revealed a 70% reduced wear rate in comparison with non-stretched samples. Microscopic examination (light microscopy, scanning electron microscopy) showed abrasive scratches in all test samples, but only in the non-stretched specimens were signs of pitting found. Translating these results to unidirectional tractive rolling on the tibial plateau in the knee joint suggests that a significant reduction in polyethylene wear can be expected. However, further experimental investigations need to be carried out to confirm this highly promising possibility.

Elasticity↗
PubMed2003

Presentation of gamma-irradiated-in-air polyethylene wear in the form of a synovial cyst.

The increased wear of polyethylene sterilized with gamma irradiation in air has well been documented in the total knee arthroplasty literature. Our case report describes a patient with a well-functioning total knee replacement presenting with wear debris synovitis in the form of a large synovial cyst. We discuss this patient's preoperative evaluation, intraoperative findings, and postoperative outcome after synovectomy and polyethylene exchange. We also review the current literature on appropriate polyethylene sterilization methods.

Aged↗
PubMed2006

High density porous polyethylene material (Medpor) as an unwrapped orbital implant.

OBJECTIVE: To introduce the clinical effect among patients who received an unwrapped orbital implant with high density porous polyethylene material (Medpor) after enucleation or evisceration. METHODS: Retrospective analysis of a series of 302 patients with anophthalmia who underwent placement of an unwrapped high density porous polyethylene orbital implant. We compared the patients (n=180) who accepted primary implant placement with those (n=122) who accepted secondary implant placement. Parameters evaluated included: age at time of surgery, date of surgery, sex, implant type and size, surgery type, the surgical procedure and technique performed, and complications. RESULTS: The time of follow-up ranged from 2.0 to 58.0 months (mean 32.5 months). A total of 5 of 302 (1.66%) cases had documented postoperative complications. The following problems were noted after surgery: implant exposure, 3 patients (0.99%); implant removed due to orbital infection, 1 patient (0.34%); ptosis, 1 patient (0.34%). There were no significant complications observed in other 297 cases and all implants showed good orbital motility. The clinical effect of primary implant placement is better than that of secondary placement. CONCLUSION: High density porous polyethylene material can be used successfully as an unwrapped orbital implant in anopthalmic socket surgery with minimal complications. The material is well tolerated, nonantigenic and has low rate of infection and migration.

Adolescent↗
PubMed1993

Failure of the porous-coated anatomic prosthesis in total knee arthroplasty due to severe polyethylene wear.

Four hundred and eighty-seven total knee arthroplasties were performed by a single surgeon with use of a porous-coated anatomic prosthesis between 1982 and 1989. There were thirty-two clinical failures (7 per cent) due to severe wear of the surfaces of the tibial and patellar polyethylene components. Thirty patients had a revision. The average time to failure of the implant was four and one-half years. The initial clinical symptoms of failure by wear consisted of a painless effusion with a decreased range of motion. Subsequent pain was considered as the criterion for failure necessitating operative intervention. Increased weight and decreased age of the patient and a thinner tibial component were significant predictors of an increased risk of failure (p < 0.01). Examination of retrieved tibial components revealed extensive delamination caused by fracture of the polyethylene at a depth of about one millimeter below the surface. Cracks that had propagated in from the medial and lateral peripheries of the tibial component toward the center of the condyles were also a common finding. It appears that the design of the implant as well as clinical factors (the age and weight of the patient) contributed to the mechanical failure of the polyethylene of these implants.

Aged↗
PubMed2001

Tibial post wear in posterior stabilized total knee arthroplasty. An unrecognized source of polyethylene debris.

BACKGROUND: With extensive use of posterior stabilized total knee arthroplasty implants, it is increasingly important to assess the mechanical performance of this design alternative. The purpose of this study was to examine the wear patterns at the femoral cam-tibial post interface in a series of posterior stabilized prostheses retrieved at revision arthroplasty. METHODS: Qualitative and quantitative wear analysis was performed over the surface of the stabilizing posts from twenty-three retrieved total knee components that had been implanted for a mean of 35.6 months (range, 2.3 to 107.2 months). The implants were designs from four different manufacturers. Digital images of the anterior, posterior, medial, and lateral surfaces of the tibial post were made for quantitative analysis and determination of a post wear score. Wear was characterized with a grading system that isolates adhesive, abrasive, and fatigue wear, inferring a weighted score from an estimation of generated polyethylene debris. RESULTS: Evidence of wear or damage was observed on all twenty-three of the stabilizing posts, including those revised because of infection. On the average, 39.9% (range, 18.5% to 60%) of the post surface demonstrated some form of deformation, with adhesive wear, or burnishing, being the predominant wear mechanism. Seven posts (30%) exhibited severe damage with gross loss of polyethylene. The wear caused premature failure and early revision of two components: one of these failures was related to isolated post wear and the other, to severe post wear and subsequent fracture. Overall, wear was primarily posterior, but wear over the anterior, medial, and lateral surfaces was also notable. CONCLUSIONS: The cam-post articulation in posterior stabilized implants can be an additional source of polyethylene wear debris. The variability in wear patterns observed among designs may be due to differences in cam-post mechanics, post location, and post geometry. The surgeon should be aware that the cam-post interface is not an innocuous articulation, and manufacturers should be motivated to produce implants that maintain the function of the post while limiting wear and surface damage.

Humans↗
PubMed2002

Surface damage in machined ram-extruded and net-shape molded retrieved polyethylene tibial inserts of total knee replacements.

BACKGROUND: Polyethylene wear has emerged as a major determining factor in the long-term clinical performance of total knee replacements. This study addresses the in vivo wear performance of two types of polyethylene tibial inserts used in similar total knee arthroplasty designs. METHODS: A surface damage assessment of retrieved specimens was performed for twenty-six net-shape molded tibial inserts manufactured from H1900 resin without calcium stearate additive (Miller-Galante) and forty-three machined ram-extruded tibial inserts manufactured from GUR 4150 resin with calcium stearate additive (Miller-Galante II). Stereomicroscopic inspection and digital image analysis were used to quantify the extent and severity of pitting, dimensional change, and delamination. RESULTS: Pitting and dimensional change were the most common modes of damage in both groups, with the prevalence ranging from 77% to 92% for pitting and from 51% to 81% for dimensional change. Delamination was the least common mode of damage, with the prevalence ranging from 21% to 35%. The severity of pitting was higher in association with the cemented implant-bone interface. The extent and severity of delamination increased with implantation time. No severe delamination was observed before sixty months after implantation in the net-shape molded group, whereas severe delamination was present as early as ten months after implantation in the machined ram-extruded group. The time between surgery and the discovery of damage was longer in the net-shape molded group for all modes of damage except for medial dimensional change. CONCLUSIONS: On the basis of the components available in our implant retrieval pool, we found that at equivalent levels of surface damage, the net-shape molded H1900 resin tibial inserts demonstrated longer service life than did the machined ram-extruded GUR 4150 components. The superior performance of the net-shape molded components may be related to the resin type, the absence of calcium stearate, the consolidation method, or the method of final geometry shaping. This superior damage resistance is expected to contribute to superior long-term clinical performance of net-shape molded ultra-high molecular weight polyethylene in total knee arthroplasty.

Adult↗
PubMed2003

Comparison of two and three-dimensional computerized polyethylene wear analysis after total hip arthroplasty.

BACKGROUND: The accurate determination of acetabular polyethylene wear in vivo is necessary to assess the clinical performance of the bearing surfaces of total hip replacements. Our objective in this study was to determine the clinical performance of two and three-dimensional computerized wear analysis and to assess the implications of this performance on requirements for patient enrollment in studies designed to detect wear of total hip prostheses. METHODS: Two and three-dimensional digital computerized analyses of acetabular polyethylene wear were performed on 153 hips in 140 patients. The acetabular components consisted of a polyethylene insert in a titanium shell, articulating with a 28-mm cobalt-chromium femoral component. The average duration of radiographic follow-up was 8.4 years. The correlation coefficient for two-dimensional versus three-dimensional analysis was calculated, as was the difference between the wear detected by the two techniques. The same observer analyzed each image twice, allowing an assessment of the repeatability of the two-dimensional and three-dimensional analyses. The impact of the clinical performance of each technique on the sample size needed for adequate power in prospective studies was evaluated. RESULTS: There was a high correlation between two-dimensional and three-dimensional wear analysis (r (2) = 0.933). In thirty-one (5.2%) of 595 observations, the wear values derived with the two-dimensional and three-dimensional techniques were not consistent. Logistic regression demonstrated that acetabular anteversion had a significant effect on the likelihood of such inconsistency occurring. The two-dimensional technique detected 90.1% of the total linear wear subsequently detected by the three-dimensional analysis. The average wear value was 1.09 mm as detected by two-dimensional analysis and 1.21 mm as detected by three-dimensional analysis. The two-dimensional technique was four times more repeatable than the three-dimensional technique. Power analysis indicated that up to 1.4 times more patients need to be enrolled if the three-dimensional technique is used for wear analysis. CONCLUSIONS: While three-dimensional analysis detected 10% more wear, its repeatability was four times worse than that of the two-dimensional technique and, as a consequence, patient enrollment requirements for wear detection were higher. The poor quality of the lateral radiographs contributed to the decrease in the repeatability of the three-dimensional analysis. Three-dimensional analysis may be useful for highly anteverted cups, but the limited improvement in wear detection achieved with that technique, coupled with its inferior repeatability, limits its clinical value.

Arthroplasty, Replacement, Hip↗