Conventional Polyethylene Liners Research Articles

Analysis of Femoral Components of Cemented Total Hip Arthroplasty

There have been continuous on-going revisions in design of prosthesis in Total Hip Arthroplasty (THA) to improve the endurance of hip replacement. In the present work, Finite Element Analysis was performed on cemented THA with CoCrMo trapezoidal, CoCrMo circular, Ti6Al4V trapezoidal and Ti6Al4V circular stem. It was observed that cross section and material of femoral stem proved to be critical parameters for stress distribution in femoral components, distribution of interfacial stress and micro movements. In the first part of analysis, designs were investigated for micro movements and stress developed, for different stem materials. Later part of the analysis focused on investigations with respect to different stem cross sections. Femoral stem made of Titanium alloy (Ti6Al4V) resulted in larger debonding of stem at cement-stem interface and increased stress within the cement mantle in contrast to chromium alloy (CoCrMo) stem. Thus, CoCrMo proved to be a better choice for cemented THA. Comparison between CoCrMo femoral stem of trapezium and circular cross section showed that trapezoidal stem experiences lesser sliding and debonding at interfaces than circular cross section stem. Also, trapezium cross section generated lower peak stress in femoral stem and cortical femur. In present study, femur head with diameter of 36 mm was considered for the analysis in order to avoid dislocation of the stem. Also, metallic femur head was coupled with cross linked polyethylene liner as it experiences negligible wear compared to conventional polyethylene liner and unlike metallic liner it is non carcinogenic.

Do new materials improve acetabular fixation and reduce wear? Commentary on an article by David C. Ayers, MD, et al.: "radiostereometric analysis study of tantalum compared with titanium acetabular cups and highly cross-linked compared with conventional liners in young patients undergoing total hip replacement".

Commentary The bearing articulation remains the nemesis of total hip arthroplasty. Obtaining and maintaining component stability and minimizing wear of the articulation represent the two most important factors for the longevity of any hip replacement. This article by Ayers et al. evaluates the stability of two different types of cementless fixation, a titanium fiber mesh compared with ultra-porous tantalum. The authors further investigate wear of an ultra-high molecular weight conventional polyethylene liner compared with a highly cross-linked polyethylene liner. This article represents a sequel to a previously published two-year follow-up evaluation of noncemented total hip arthroplasty acetabular migration and polyethylene wear as determined by radiostereometric analysis (RSA)1. A total of forty-six young, active individuals undergoing primary total hip arthroplasty were randomized into four cohorts: ultra-high molecular weight conventional polyethylene liner and titanium cup, highly cross-linked polyethylene liner and titanium cup, ultra-high molecular weight conventional polyethylene liner and tantalum cup, and highly cross-linked polyethylene liner and tantalum cup. There were no clinical or non-RSA radiographic differences among the groups. RSA demonstrated significantly less femoral head penetration, a surrogate for polyethylene wear, in the highly cross-linked polyethylene liners compared with ultra-high molecular weight conventional polyethylene liners by an order of magnitude. There was no significant difference in proximal migration between the titanium and tantalum acetabular components through five years of follow-up. The type of polyethylene liner or acetabular component had no effect on patient activity, pain, and well-being, which were maximized by six months following surgical intervention. The strength of this article is that it is a prospective, randomized, blinded study utilizing a very sophisticated technology, namely RSA, to obtain precise measurements of component micromotion relative to the bone that is otherwise undetectable by routine radiographs and to measure femoral head penetration2. The radiodense tantalum cups obscure the identification of the center of the femoral head with use of edge detection. Therefore, Ayers et al. developed a novel method known as the “fictive femoral head” to assess wear. This method is based on the identification of two radiopaque tantalum markers attached to the stem proximally and a priori knowledge of the femoral head and stem configuration of the inserted total hip replacement. From a series of radiographs, a stem configuration library was created, which provided geometrical information used to place a fictive femoral head center in three-dimensional space. This fictive femoral head center will be used by the RSA software. Although others have reported a substantial decrease in the wear of highly cross-linked polyethylene3, this article clearly shows the superiority of highly cross-linked polyethylene over conventional polyethylene, with a tenfold reduction in wear. Wear rates from one to five years were 0.04 mm/yr for ultra-high molecular weight conventional polyethylene liners and 0.004 mm/yr for highly cross-linked polyethylene liners. With respect to fixation, Ayers et al. demonstrated excellent fixation of both titanium mesh and tantalum acetabular components, as has been previously documented4. At the five-year follow-up, the median migration (and standard error) was 0.05 ± 0.20 mm proximally for titanium mesh cups and 0.21 ± 0.05 mm for tantalum cups. No implants were shown to be loose on radiographs. There was no evidence of osteolysis and no revisions were performed through five years of follow-up. The take-home points from this article are as follows. With use of femoral head penetration according to precise RSA measurements as a surrogate for wear, highly cross-linked polyethylene demonstrates ten times lower wear than ultra-high molecular weight conventional polyethylene at up to five years of follow-up3. Titanium mesh and tantalum (Trabecular Metal; Zimmer) materials provide excellent cementless fixation for acetabular components with little evidence of clinically relevant migration as measured by sophisticated RSA technology at up to five years of follow-up4. These results cannot and should not be extrapolated to other types of porous and ultra-porous cementless fixation.

Influence of Pelvic Tilt on Polyethylene Wear after Total Hip Arthroplasty.

We aimed to evaluate the effects of pelvic tilt on polyethylene wear after total hip arthroplasty (THA). A total of 105 joints treated with primary THA were included; conventional polyethylene (CPE) liners were used in 43 hips and highly cross-linked polyethylene (HXLPE) liners were used in the remaining 62 hips. The pelvis was tilted 6° posteriorly in the standing position as compared to the supine position, which resulted in significant increases of 1.7° and 2.8° in cup inclination in the CPE and HXLPE groups, respectively. Moreover, the change in pelvic tilt resulted in significant increases of 3.6° and 4.9° in cup anteversion in the CPE and HXLPE groups, respectively. For the CPE group, multiple regression analysis showed a significant association between the angle of pelvic tilt (PTA) and cup inclination and the polyethylene wear ratio. The adjusted R 2 of the regression model was larger for measures obtained in the standing position as compared to the supine position. For the HXLPE group, there was no significant relationship between radiographic parameters and polyethylene wear. Close observation of polyethylene wear is recommended for patients with severe posterior pelvic tilt who have undergone THA with conventional polyethylene.

Wear of a sequentially annealed polyethylene acetabular liner

Background and purpose — We previously reported on a randomized controlled trial (RCT) that examined the effect of adding tobramycin to bone cement after femoral stem migration. The present study examined femoral head penetration into both conventional and highly crosslinked polyethylene acetabular liners in the same group of RCT patients, with a minimum of 5 years of postoperative follow-up.Patients and methods — Linear penetration of the femoral head into an X3 (Stryker) crosslinked polyethylene (XLPE) liner was measured in 18 patients (19 hips) using radiostereometric analysis (RSA). Femoral head penetration was also measured in 6 patients (6 hips) with a conventional polyethylene liner (CPE), which served as a control group.Results — The median proximal femoral head penetration in the XLPE group after 5.5 years was 0.025 mm with a steady-state penetration rate of 0.001 mm/year between year 1 and year 5. The CPE liner showed a median proximal head penetration of 0.274 mm after 7.2 years, at a rate of 0.037 mm/year.Interpretation — The Trident X3 sequentially annealed XLPE liner shows excellent in vivo wear resistance compared to non-crosslinked CPE liners at medium-term implantation. The rate of linear head penetration in the XLPE liners after > 5 years of follow-up was 0.001 mm/year, which is in close agreement with the results of previous studies.

Highly crosslinked polyethylene improves wear but not surface damage in retrieved acetabular liners.

Highly crosslinked polyethylene (XLPE) is believed to demonstrate better wear resistance than conventional polyethylene (CPE) in total hip arthroplasty. The purpose of this study was to compare visual damage scores and micro-CT measurements of penetration, a surrogate for wear, between matched retrieved XLPE and CPE acetabular liners. Thirteen XLPE acetabular liners were matched in terms of implant design (all were of the same design), patient age, sex, liner dimensions, duration of implantation, and reason for revision to a group of CPE liners that were retrieved in the same time period. Penetration resulting from the combination of wear and creep in the two groups of liners was measured with micro-CT. Surface damage was scored by two blinded observers using a surface damage system that considers the seven common damage modes: pitting, scratching, burnishing, abrasions, impingement, embedded debris, and delamination, and wear patterns were documented. There was no difference (p=0.32) in total damage score between the XLPE group (14±4) and the CPE group (15±5). However, there was three times greater penetration (odds ratio, 3.1; confidence interval, 2.3-5.1; p<0.001) in the CPE group (0.18±0.09 mm/year) than in the XLPE group (0.05±0.07 mm/year). There was less volumetric loss in XLPE (82±SD 134 mm3) versus the CPE group (350±SD 342 mm3; p=0.017). XLPE liners undergo less penetration as a result of creep and wear than CPE liners based on quantitative measurements provided by micro-CT, which was not apparent using damage scoring alone. This demonstrates the use of three-dimensional imaging techniques such as micro-CT for quantifying wear in retrieval studies. In this study, XLPE had less wear but similar damage scores than CPE, allaying concerns that the beneficial wear properties of XLPE might come with a tradeoff arising from the increased brittleness of that material.

Wear rates of highly cross-linked polyethylene humeral liners subjected to alternating cycles of glenohumeral flexion and abduction

Although short-term outcomes of reverse total shoulder arthroplasty have been promising, long-term success may be limited due to device-specific complications, including scapular notching. Scapular notching has been explained primarily as mechanical erosion; however, the generation of wear debris may lead to further biologic changes contributing to the severity of scapular notching. A 12-station hip simulator was converted to a reverse total shoulder arthroplasty wear simulator subjecting conventional and highly cross-linked ultra-high-molecular-weight polyethylene humeral liners to 5 million cycles of alternating abduction-adduction and flexion-extension loading profiles. Highly cross-linked polyethylene liners (36.5±10.0mm(3)/million cycle) exhibited significantly lower volumetric wear rates compared with conventional polyethylene liners (83.6±20.6mm(3)/million cycle; P<.001). The flexion-extension loading profile exhibited significantly higher wear rates for conventional (P<.001) and highly cross-linked polyethylene (P<.001) compared with the abduction-adduction loading profile. Highly cross-linked wear particles had an equivalent circle diameter significantly smaller than wear particles from conventional polyethylene (P<.001). Highly cross-linked polyethylene liners significantly reduced polyethylene wear and subsequent particle generation. More favorable wear properties with the use of highly cross-linked polyethylene may lead to increased device longevity and fewer complications but must be weighed against the effect of reduced mechanical properties.

Long-Term Performance of Ceramic and Metal Femoral Heads on Conventional Polyethylene in Young and Active Patients

Ceramic femoral heads produce less wear of the opposing polyethylene than do metal femoral heads in wear simulation studies. This is a matched-pair analysis of the wear of ceramic and metal femoral heads on conventional polyethylene in uncemented total hip replacements in young, active patients at a minimum of fifteen years of follow-up. From June 1989 to May 1992, thirty-one matched pairs of alumina ceramic or cobalt-chromium metal femoral heads were identified. Patients were matched on the basis of age, sex, body weight, diagnosis, and activity level. The mean age was 55 ± 9 years (range, twenty-three to sixty-five years) at the time of surgery. All procedures were performed with a posterolateral surgical approach by a single surgeon using press-fit Ranawat-Bernstein femoral stems, Harris-Galante-II acetabular cups, GUR 4150 conventional polyethylene (sterilized in argon), and 28-mm-diameter femoral heads. Wear measurements were performed by two independent observers using the computer-assisted Roman software. The average duration of follow-up was 17 ± 1.7 years (range, fifteen to twenty years). The mean Hospital for Special Surgery hip scores (and standard deviation) in the ceramic and metal groups were 39 ± 4 and 40 ± 3 at the time of final follow-up. The University of California Los Angeles activity score at the time of the final follow-up was 6 ± 2 for both groups. The mean wear rates for the ceramic group and the metal group were 0.086 ± 0.05 mm/yr and 0.137 ± 0.05 mm/yr, respectively (p = 0.0015). There was one reoperation in the ceramic group because of distal femoral osteolysis. There were three failures in the metal group, requiring isolated liner exchange in two hips and revision of the acetabular component in one hip because of wear-induced osteolysis and/or loosening that caused symptoms. Five hips in the ceramic group and six hips in the metal group had radiographic evidence of acetabular or femoral osteolysis, but none were symptomatic. Ceramic femoral heads produced significantly less wear on conventional polyethylene liners at the time of long-term follow-up than did metal heads in this matched-pair analysis of young and active patients with uncemented fixation.

Characteristics of highly cross-linked polyethylene wear debris in vivo.

Despite the widespread implementation of highly cross-linked polyethylene (HXLPE) liners to reduce the clinical incidence of osteolysis, it is not known if the improved wear resistance will outweigh the inflammatory potential of HXLPE wear debris generated in vivo. Thus, we asked: What are the differences in size, shape, number, and biological activity of polyethylene wear particles obtained from primary total hip arthroplasty revision surgery of conventional polyethylene (CPE) versus remelted or annealed HXLPE liners? Pseudocapsular tissue samples were collected from revision surgery of CPE and HXLPE (annealed and remelted) liners, and digested using nitric acid. The isolated polyethylene wear particles were evaluated using scanning electron microscopy. Tissues from both HXLPE cohorts contained an increased percentage of submicron particles compared to the CPE cohort. However, the total number of particles was lower for both HXLPE cohorts, as a result there was no significant difference in the volume fraction distribution and specific biological activity (SBA; the relative biological activity per unit volume) between cohorts. In contrast, based on the decreased size and number of HXLPE wear debris there was a significant decrease in total particle volume (mm(3)/g of tissue). Accordingly, when the SBA was normalized by total particle volume (mm(3)/gm tissue) or by component wear volume rate (mm(3)/year), functional biological activity of the HXLPE wear debris was significantly decreased compared to the CPE cohort. Indications for this study are that the osteolytic potential of wear debris generated by HXLPE liners in vivo is significantly reduced by improvements in polyethylene wear resistance.

Ceramic Head Fracture in Ceramic-on-Polyethylene Total Hip Arthroplasty

Revision rates of total hip arthroplasty have decreased after introducing total hip arthroplasty (THA) using ceramic component, since ceramic components could reduce components wear and osteolysis. The fracture of a ceramic component is a rare but potentially serious event. Thus, ceramic on polyethylene articulation is gradually spotlighted to reduce ceramic component fracture. There are a few recent reports of ceramic head fracture with polyethylene liner. Herein, we describe a case of a ceramic head component fracture with polyethylene liner. The fractured ceramic head was 28 mm short neck with conventional polyethylene liner. We treated the patient by total revision arthroplasty using 4th generation ceramic on ceramic components.

What an Orthopedic Surgeon Should Know: Selection of a Bearing Couple in Case of Revision After a Fractured Ceramic Component

Revision surgery for fractured ceramic components in total hip arthroplasty (THA) potentially leaves small ceramic fragments in the joint capsule, and the fragments might become embedded in polyethylene (PE) acetabular liners. The purpose of this study was to determine the wear behavior of metal femoral ball heads and ceramic femoral ball heads tested with highly cross-linked and conventional polyethylene liners in the presence of ceramic debris. A worst-case scenario, assuming embedding of ceramic fragments in the PE liner, contamination of the test environment with third-body ceramic debris and continuous subluxation, was simulated in vitro. High wear rates were found for metal femoral ball heads, being 1,010 times higher when compared to ceramic femoral ball heads tested with XPE liners and 560 times higher when compared to ceramic femoral ball heads tested with PE liners. The test results indicate the use of ceramic femoral ball heads for revision surgery in the presence of ceramic fragments.

Liner Exchange Into A Well Fixed Acetabular Shell In Revision Total Hip Arthroplasty

Objective To investigate clinical outcomes and complications of isolated polyethylene liner exchange for revision total hip arthroplasty.Methods From April 1995 to December 2007,80 patients (93 hips) underwent revision total hip arthroplasty during which only polyethylene liner was exchanged with reservation of acetabular cup.There were 41 males and 39 females,aged from 27 to 82 years (average,53.3 years).The duration from the primary THA to the revision surgery ranged from 0.3 to 18.4 years (average,10.9 years).The reasons for liner exchange included:polyethylene wear with osteolysis (78 hips),polyethylene wear without osteolysis (5 hips),polyethylene wear with stem loosening (4 hips),recurrent dislocation (3hips),infection (1 hip),periprosthetic fracture (1 hip) and liner dislodgement (1 hip).Forty-seven liners were fixed into the old cup using cement,and 46 were fixed with the original locking mechanism.Sixty cross-linked polyethylene liners and 33 conventional polyethylene liners were used.Results All patients were followed up for 5 to 15 years (average,7 years).The average Harris hip score improved from preoperative 86.0±16.9 to 89.4±11.6 at final follow-up.Complications included dislocation (10 hips),infection (2 hips),periprosthetic fracture (1 hip) and liner dislodgement (1 hip).Ten hips underwent rerevision due to different reasons:cup exchange (5 hips),conventional polyethylene wear (2 hips),infection (2 hips) and liner dislodgement (1 hip).Using component loosening as the end point,the 10-year survival rate was 100％ in the cement fixation group and 84.8％ in the original locking group.Using rerevision as the end point,the 10-year survival rate was 90.4％ in the cement fixation group and 65.0％ in the original locking group.Conclusion Liner exchange either with cement or original locking mechanism is a safe and successful method.Highly cross-linked polyethylene has a higher wear resistance,which can reduce incidence of osteolysis and improve survival rate of prosthesis. Key words: Arthroplasty, replacemrnt, hip; Reoperation; Polyethylene; Osteolysis

Repeated Ceramic Head Fracture after Ceramic-on-ceramic Total Hip Arthroplasty

Early generation ceramic articulations were problematic in terms of ceramic implant fracture and wear. Although the mechanical properties of ceramic material have improved during the last three decades, ceramic component fracture remains an issue. Many authors have reported fractures of the ceramic head, and a few have described ceramic acetabular insert fracture. However, these complications are only encountered rarely, and all cases reported to date involve a history of minor trauma. Here, we describe a case that required 2ndrevision with a CoCr metal head and conventional polyethylene liner due to a recurrent fracture of the ceramic head.

Scratching Vulnerability of Conventional vs Highly Cross-Linked Polyethylene Liners Because of Large Embedded Third-Body Particles

The hypothesis of this study was that acetabular liner vulnerability to scratching from femoral heads, roughened by third bodies embedded in the liner, is not significantly lower for highly cross-linked polyethylene (HXPE) than for conventional polyethylene (CPE). Six CPE and 6 HXPE acetabular liners were each reproducibly embedded with 5 cobalt-chromium-molybdenum (CoCrMo) beads then run for 10 000 cycles in a joint simulator. By visual rank ordering, there was low association between liner scratch severity and polyethylene type. The CPE and HXPE liner scratches were not significantly different in scratch peak-valley height or width or in liner roughness in the vicinity of the embedded beads. This model indicated that high cross-linking of polyethylene does not offer appreciable protection against severe scratching induced by large embedded third-body particles.

Cross-linkedversusconventional polyethylene for total hip replacement

We conducted a systematic review and meta-analysis of randomised controlled trials comparing cross-linked with conventional polyethylene liners for total hip replacement in order to determine whether these liners reduce rates of wear, radiological evidence of osteolysis and the need for revision. The MEDLINE, EMBASE and COCHRANE databases were searched from their inception to May 2010 for all trials involving the use of cross-linked polyethylene in total hip replacement. Eligibility for inclusion in the review included the random allocation of treatments, the use of cross-linked and conventional polyethylene, and radiological wear as an outcome measure. The pooled mean differences were calculated for bedding-in, linear wear rate, three-dimensional linear wear rate, volumetric wear rate and total linear wear. Pooled risk ratios were calculated for radiological osteolysis and revision hip replacement. A search of the literature identified 194 potential studies, of which 12 met the inclusion criteria. All reported a significant reduction in radiological wear for cross-linked polyethylene. The pooled mean differences for linear rate of wear, three-dimensional linear rate of wear, volumetric wear rate and total linear wear were all significantly reduced for cross-linked polyethylene. The risk ratio for radiological osteolysis was 0.40 (95% confidence interval 0.27 to 0.58; I(2) = 0%), favouring cross-linked polyethylene. The follow-up was not long enough to show a difference in the need for revision surgery.

The Incidence of Acetabular Osteolysis in Young Patients With Conventional versus Highly Crosslinked Polyethylene

Osteolysis is a major mode of hip implant failure. Previous literature has focused on the amount of polyethylene wear comparing highly crosslinked polyethylene (HXPLE) with conventional liners but has not clarified the relative incidence of osteolysis with these two liners. We determined (1) the incidence of osteolysis in HXLPE versus conventional polyethylene (CPE), (2) the ability to detect and evaluate the size of lytic lesions using radiographs compared with CT scans, (3) head penetration in hips without and with lysis, and (4) determined whether acetabular position, head size, and UCLA activity score contributed to lysis. We compared head penetration and osteolysis on plain radiographs and presence and volume of osteolysis on CT scans in 48 patients with HXLPE (mean, 46.5 years) and 50 patients with CPE (mean, 43.2 years). The minimum followup was 5 years (average, 7.2 years; range, 5.1-10.9 years), Osteolysis was apparent on CT in a larger number of patients with CPE liners than HXLPE liners: 12 of 50 (24%) versus one of 48 (2%), respectively. We found no correlation between head penetration and volume of osteolytic lesions. Head penetration was greater in patients with osteolysis. Smaller head sizes were associated with greater wear and those with osteolysis had smaller head sizes; however, there was no difference in acetabular component position or UCLA activity in those with lysis compared with those without. HXLPE diminished the incidence of osteolysis, but the lack of correlation between penetration and volume of osteolysis suggests other factors other than wear contribute to the development of osteolysis. Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

A modular femoral neck and head system works well in cementless total hip replacement for patients with developmental dysplasia of the hip

We compared a modular neck system with a non-modular system in a cementless anatomical total hip replacement (THR). Each group consisted of 74 hips with developmental hip dysplasia. Both groups had the same cementless acetabular component and the same articulation, which consisted of a conventional polyethylene liner and a 28 mm alumina head. The mean follow-up was 14.5 years (13 to 15), at which point there were significant differences in the mean total Harris hip score (modular/non-modular: 98.6 (64 to 100)/93.8 (68 to 100)), the mean range of abduction (32 degrees (15 degrees to 40 degrees )/28 (0 degrees to 40 degrees )), use of a 10 degrees elevated liner (31%/100%), the incidence of osteolysis (27%/79.7%) and the incidence of equal leg lengths (> or = 6 mm, 92%/61%). There was no disassociation or fracture of the modular neck. The modular system reduces the need for an elevated liner, thereby reducing the incidence of osteolysis. It gives a better range of movement and allows the surgeon to make an accurate adjustment of leg length.

High Stress Conditions Do Not Increase Wear of Thin Highly Crosslinked UHMWPE

Introduction of highly crosslinked polyethylene has increased interest in large femoral heads, because thin acetabular liners can be used while maintaining low wear rates and larger heads decrease the incidence of instability. However, crosslinking and subsequent thermal treatments can cause decreased mechanical properties that might obviate the reduced wear under extreme conditions. To examine whether increased contact pressures would adversely affect wear in thin liners, we tested thin and thick highly crosslinked liners (3.8 mm thickness/44-mm head and 7.9 mm thickness/36-mm head, respectively) to 5 million cycles on a hip simulator under near impingement conditions. Conventional polyethylene liners (7.9 mm thickness/36-mm head) served as controls. Large femoral heads with highly crosslinked polyethylene liners as thin as 3.8 mm in thickness do not wear at a higher rate than a thicker liner of the same material, even when subjected to large contact pressures such as occur under near-impingement conditions. Crosslinked polyethylene may allow for liners that are thinner than has been traditionally accepted. This conclusion, however, is based solely on wear test results with idealized cup position, no intentional edge loading, no head subluxation, and no artificial aging. Continued monitoring will be necessary to elucidate the clinical efficacy of these devices.

Wear Rate of Highly Cross-Linked Polyethylene in Total Hip Arthroplasty

Highly cross-linked polyethylene was introduced for clinical use in total hip arthroplasty with the expectation that it would exhibit less wear when compared with conventional polyethylene. The purpose of this study was to report the clinical and radiographic results, after a minimum of five years of follow-up, of a randomized, blinded, controlled trial comparing a conventional polyethylene with a first-generation highly cross-linked polyethylene. One hundred patients were enrolled in a prospective, randomized controlled study comparing highly cross-linked and conventional polyethylene acetabular liners in total hip arthroplasty. Fifty patients were in each group. At the time of follow-up, clinical outcomes were assessed and steady-state femoral head penetration rates (after bedding-in) for each patient were calculated with use of a validated radiographic technique. In addition, a statistical comparison of polyethylene wear between groups was performed with use of generalized estimating equations. At a mean of 6.8 years postoperatively, there were no differences between the two polyethylene groups with regard to the Harris hip score, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), or Short Form-12 (SF-12) score. The mean femoral head penetration rate in the first through fifth years was found to be significantly lower in the group treated with the highly cross-linked polyethylene (0.003 mm/yr [95% confidence interval, +/-0.027]) than it was in the group treated with conventional polyethylene (0.051 mm/yr [95% confidence interval, +/-0.022]) (p=0.006). Men treated with a conventional polyethylene liner had a significantly higher (p<or=0.012) femoral head penetration rate (0.081 mm/yr [95% confidence interval, +/-0.065]) than both men and women with a highly cross-linked liner (-0.013 mm/yr [95% confidence interval, +/-0.074] and 0.009 mm/yr [95% confidence interval, +/-0.028], respectively). The general estimating equations demonstrated that the group with a highly cross-linked polyethylene liner had a significantly lower femoral head penetration rate than the group with a conventional polyethylene liner (p=0.025), and a significantly higher femoral head penetration rate was demonstrated in men with a conventional polyethylene liner when compared with both men and women with a highly cross-linked liner (p=0.003). At a minimum of five years postoperatively, the steady-state femoral head penetration rate associated with this first-generation highly cross-linked polyethylene liner was significantly lower than that associated with a conventional polyethylene liner. Long-term follow-up is required to demonstrate the clinical benefit of this new material.

The Effect of Neutron Radiation on Conventional and Highly Cross-Linked Ultrahigh-Molecular-Weight Polyethylene Wear

The effects of a sarcoma therapy dose level neutron radiation on oxidation and wear were compared between conventional (N2\\Vac, Stryker Orthopedics, Mahwah, NJ) and highly cross-linked (Crossfire, Stryker Orthopedics) ultrahigh-molecular-weight polyethylene acetabular liners. Liners were exposed to 15 Gy, a typical sarcoma treatment dose. Wear testing was conducted on a hip simulator. Transvinylene and oxidation indices were measured to determine if significant radiolytic reactions and oxidation occurred after the neutron beam exposure. The neutron bombardment produced further oxidation in both N2\\Vac and Crossfire liners. Surprisingly, neutron radiation caused 62% increase in wear for N2\\Vac but 0% change for the Crossfire acetabular liners. This study suggested that when joint implants are exposed to neutron beam radiation therapy, the conventional polyethylene liner is at risk for rapid wear.

Wear Rate Using a Cross-Linked Polyethylene Liner Versus Conventional Polyethylene Liner in Patients Undergoing Primary Total Hip Arthroplasty

The purpose of this study was to compare wear rate of cross-linked polyethylene liners to conventional polyethylene liners at average 5-year follow-up.