HXLPE Liner Research Articles

CORR Insights®: Prediction of Polyethylene Wear Rates from Gait Biomechanics and Implant Positioning in Total Hip Replacement.

CORR Insights®: Prediction of Polyethylene Wear Rates from Gait Biomechanics and Implant Positioning in Total Hip Replacement.

The Relationship Between Polyethylene Wear and Periprosthetic Osteolysis in Total Hip Arthroplasty at 12 Years in a Randomized Controlled Trial Cohort

BackgroundPolyethylene acetabular components are common in hip arthroplasty. Highly cross-linked polyethylene (HXLPE) has lower wear than ultra-high molecular weight polyethylene (UHMWPE). Evidence suggests that wear particles induce inflammation causing periprosthetic osteolysis contributing to implant loosening with wear rates of 0.05 mm/y were considered safe. We aimed to compare incidence and volume of periacetabular osteolysis between HXLPE and UHMWPE using computed tomography. MethodsInitially, 54 hips in 53 patients were randomized to HXLPE or UHMWPE acetabular liner. At 10 years, 39 hips in 38 patients remained for the radiostereometric analysis' demonstrating significantly lower wear in the HXLPE group. At 12 years, 14 hips in 13 patients were lost to follow-up leaving 25 hips for computed tomography assessment. Images were reconstructed to detect osteolysis and where identified, areas were segmented and volumized. ResultsOsteolysis was observed in 8 patients, 7 from the UHMWPE group and only 1 from the HXLPE group (Fisher exact, P = .042). There was no correlation between the amount of polyethylene wear and osteolysis volume; however, the radiostereometric analysis-measured wear rate in patients with osteolysis from both groups was significantly higher than overall average wear rate. ConclusionThis data demonstrates lower incidence of periacetabular osteolysis in the HXLPE group of a small cohort. Although numbers are too low to estimate causation, in the context of lower wear in the HXLPE group, this finding supports the hypothesis that HXLPE may not elevate osteolysis risk, and hence does not suggest that HXLPE wear particles are more biologically active than those generated by earlier generations of polyethylene.

Alumina Delta-on-Highly Crosslinked-Remelted Polyethylene Bearing in Cementless Total Hip Arthroplasty in Patients Younger than 50 Years

BackgroundThe purpose of this retrospective study was to determine the clinical and radiographic results, prevalence of polyethylene wear and osteolysis, and fracture of alumina delta ceramic femoral head or highly crosslinked, remelted polyethylene (HXLPE) liner associated with the use of alumina delta ceramic femoral head-on-HXLPE bearing in cementless total hip arthroplasty in patients younger than 50 years. MethodsWe reviewed the cases of 119 patients (130 hips) who underwent a cementless total hip arthroplasty using alumina delta ceramic-on-HXLPE bearing when they were 50 years or younger at the time of surgery. The most common diagnoses were osteonecrosis (51%) and osteoarthritis secondary to developmental dysplastic hip (39%). Osteolysis and polyethylene wear rates were evaluated with use of radiography and computed tomography. In addition, prevalence of fracture of alumina delta ceramic head and polyethylene line was documented. The mean follow-up was 8.3 years (range, 7-9 years). ResultsThe mean Harris hip score, Western Ontario and McMaster Universities Osteoarthritis Index score, University of California, Los Angeles activity score were 94 points, 14 points, and 8.1 points, respectively, at the final follow-up. No patient had thigh pain. All acetabular components and all but one femoral components were well fixed. The mean annual penetration rate of femoral head was 0.022 ± 0.003 mm/year. No hip had osteolysis or ceramic head or HXLPE liner fracture. ConclusionOur average 8.3-year results with the use of alumina delta ceramic-on-HXLPE bearing in the patients younger than 50 years suggest that cementless acetabular and femoral components provide a high survival rate without evidence of osteolysis or ceramic head or AXLPE liner fracture.

Thirteen-Year Evaluation of Highly Cross-Linked Polyethylene Articulating With Either 28-mm or 36-mm Femoral Heads Using Radiostereometric Analysis and Computerized Tomography

BackgroundThe objective of this 13-year prospective evaluation of highly cross-linked ultra high molecular weight polyethylene (HXLPE) was to (1) assess the long-term wear of HXLPE articulating with 2 femoral head sizes using radiostereometric analysis (RSA) and to (2) determine if osteolysis is a concern with this material through the use of plain radiographs and computerized tomography (CT). MethodsAll patients received a Longevity HXLPE liner with tantalum beads and either a 28-mm or 36-mm femoral head. Twelve patients (6 in each head size group) agreed to return for 13-year RSA, plain radiograph, and CT follow-up. The 1-year and 13-year plain radiographs as well as the CT scans were analyzed for the presence of osteolysis. ResultsThe 13-year mean ± standard error steady-state wear was 0.05 ± 0.02 mm with no significant increase over time or between the 2 head size groups. Two patients’ CT scans showed radiolucent regions in the acetabulum of 4.51 cm3 and 11.25 cm3, respectively. In one patient, this area corresponded to a partially healed degenerative cyst treated with autograft during surgery. The second patient had an acetabular protrusio treated with autograft, and the CT scan revealed areas of remodeling of this graft. One patient’s 13-year plain radiographs showed evidence of cup loosening and linear radiolucencies in zones 2 and 3. ConclusionThere was no evidence of significant wear over time using RSA. The CT scans did not show evidence of osteolysis due to wear particles. These results suggest that this material has reduced wear compared to conventional polyethylene, irrespective of head size.

A forty millimetre head significantly improves range of motion compared with a twenty eight millimetre head in total hip arthroplasty using a computed tomography-based navigation system.

Larger-diameter (≥40mm) femoral heads decrease the incidence of post-operative dislocation in total hip arthroplasty (THA). This study was conducted to discover whether larger-diameter femoral heads result in greater range of motion of the hip with the use of a computed tomography (CT)-based navigation system. Thirty-nine primary THAs were performed via a posterolateral approach using a CT-based navigation system. The stem was inserted in the femur in line with the original femoral neck anteversion. Considering the range of motion during various daily activities which could occur without impingement, the cup anteversion was decided at 10 ° increments according to the stem anteversion. While the cup inclination was set at 40 ° in order to avoid a high inclination angle to prevent the edge roading between the HXLPE liner and ceramic head. After implantation, trial liners and femoral heads were used with either 28 or 40 mm diameter. Maximal hip flexion, extension, abduction, external rotation in extension at 0° and internal rotation angles in flexion at 90 ° were measured. The differences between the ranges of motion with the 40-mm and 28-mm heads were tested. The results were assessed with paired Student t-tests. The ranges of motion in flexion, extension, abduction and internal rotationangles improved significantly with the 40-mm heads compared with the 28-mm heads. The ranges of motionof cases where maximal flexion angle was 90° or less were excluded, improved significantly with the 40 mm heads. We concluded that the larger-diameter 40-mm femoral prosthetic heads result in greater ranges of motion in flexion, extension, abduction and internal rotation.

Gender Differences in Wear Rates for 28- vs 32-mm Ceramic Femoral Heads on Modern Highly Cross-linked Polyethylene at Midterm Follow-Up in Young Patients Undergoing Total Hip Arthroplasty

BackgroundWe report on the midterm linear and volumetric wear of highly cross-linked polyethylene (HXLPE) and survivorship of 2 prospective young total hip arthroplasty (THA) cohorts that differed by the size of ceramic femoral head used: 28 vs 32 mm. MethodsWe prospectively analyzed 220 consecutive primary THAs in patients aged ≤50 years who received a cementless THA with a ceramic femoral head on HXLPE liner (C-HXLPE). There were 101 patients (46%) with 28-mm heads and 119 patients (54%) who received 32-mm heads at a mean follow-up of 5.5 years (range, 60-109 months). Wear was calculated using Martell Software. ResultsThe 28-mm C-HXLPE cohort demonstrated average linear and volumetric wear of 0.020 mm/y (standard deviation [SD], 0.074; 95% CI, 0.003-0.037) and 18.775 mm3/y (SD, 21.743; 95% CI, 13.773-23.778) compared with 0.032 mm/y (SD, 0.087; 95% CI, 0.013-0.050]) and 29.847 mm3/y (SD, 35.441; 95% CI, 22.294-37.401) in the 32-mm C-HXLPE group. Subgroup analysis by gender and head size discovered significantly greater wear in females with 32-mm heads compared with 28-mm heads in both linear (0.01, 95% CI = −0.014 to 0.033 vs 0.048, 95% CI = 0.022-0.074 mm/y, P = .004) and volumetric wear (14.11, 95% CI = 8.957-19.271] vs 29.71, 95% CI = 17.584-41.840] mm3/y, P = .009). We found a 96% (95% CI = 92.30%-97.94%]) survivorship by Kaplan-Meier analysis at minimum 5 years with no failures because of osteolysis. ConclusionsCeramic on HXLPE demonstrates extremely low wear properties in young patients at midterm follow-up. We identified a gender-dependent difference in wear based on head size, with 32-mm heads being associated with increased wear in females.

In-vivo degradation of middle-term highly cross-linked and remelted polyethylene cups: Modification induced by creep, wear and oxidation

In this study Raman (RS) and Fourier Transform Infrared (FT-IR) spectroscopic techniques were exploited to study 11 retrieved liners made of remelted highly cross-linked polyethylene (HXLPE), with the intent to elucidate their in-vivo mechanical and chemical degradation. The retrievals had different follow-ups, ranging from a few months to 7 years of implantation time and belong to the first generation of highly cross-linked and remelted polyethylene clinically introduced in 1999, but still currently implanted. Raman assessments enabled to discriminate contributes of wear and creep on the total reduction of thickness in different locations of the cup. According to our results, although the most of the viscoelastic deformation occurred during the first year (bedding-in period), it progressed during the steady wear state up to 7 years with much lower but not negligible rate. Overall, the wear rate of this remelted HXLPE liner was low. Preliminary analysis on microtomed sections of the liners after in-vivo and in-vitro accelerated aging (ASTM F2003-02) enabled to obtain a phenomenological correlation between the oxidation index (OI) and the amount of orthorhombic phase fraction (αc), which can be easily non-destructively measured by RS. Profiles of αc obtained from different locations of the cups were used to judge the oxidative degradation of the 11 retrievals, considering also the ex-vivo time elapsed from the revision surgery to the spectroscopic experiments. Low but measurable level of oxidation was detected in all the short-term retrievals, while in the middle-term samples peaks of OI were observed in the subsurface (up to OI=4.5), presumably induced by the combined effect of mechanical stress, lipid absorption and prolonged ex-vivo shelf-aging in air.

CORR Insights®: Retrieval analysis of sequentially annealed highly crosslinked polyethylene used in total hip arthroplasty.

I n vivo oxidation of highly crosslinked polyethylene (HXLPE) components, particularly among annealed polyethylenes, resulted in the development of the so-called ‘‘secondgeneration HXLPEs’’ (defined as HXLPEs that incorporate manufacturing modifications to improve minor deficiencies with unclear consequences). Among those, sequentially annealed polyethylenes were designed to decrease the detected in vivo oxidation that could adversely affect the durability of these components in vivo. Radiostereometric analysis of THAs using sequentially annealed secondgeneration HXLPE liners suggested that head penetration and threedimensional wear remained low at 5 years [1]. However, recent retrieval studies [2, 3] stressed the persistence of oxidation in the HXLPE in the face of remelting, annealing, or sequential annealing. While in vivo oxidation was higher in the tibial retrievals than in the acetabular liners, the debate regarding this topic continues. The location and mechanical effects of residual oxidation that develops in vivo may influence the risk of component failure, in particular in THAs.

Effect of femoral head size on metal-on-HXLPE hip arthroplasty outcome in a combined analysis of six national and regional registries.

HXLPE (highly cross-linked polyethylene) has greater wear resistance compared with UHMWPE (ultra-high molecular weight polyethylene), which may contribute to improving the outcomes of total hip arthroplasty with a large femoral head. However, no information is available regarding the effect of femoral head size on the survivorship of HXLPE hip prostheses. The aim of the present study was to provide evidence regarding whether femoral head size has an effect on the risk of revision when an HXLPE liner is used on a metal head. A distributed health data network was developed by the ICOR (International Consortium of Orthopaedic Registries). Six national and regional registries are participating in this network: Kaiser Permanente, HealthEast, the Emilia-Romagna region in Italy, the Catalan region in Spain, Norway, and Australia. Data from each registry were standardized and provided at an aggregate level for each of the variables of interest. Patients with osteoarthritis who were forty-five to sixty-four years of age and had undergone uncemented total hip arthroplasty were included in the present study. Analyses were performed on the basis of individual patient profiles, utilizing the variables collected from each registry. The outcome of interest was the time to the first revision (for any reason). Survival probabilities and their standard errors were extracted from each registry for each unique combination of the covariates and were combined through multivariate meta-analysis utilizing linear mixed models to compare survivorship for <32-mm, 32-mm, and >32-mm femoral head sizes. A total of 14,372 total hip arthroplasties were included in the study. The five-year rate of revision surgery varied from 1.9% to 3.2% among registries. The risk of revision did not differ significantly between <32-mm and 32-mm head sizes (HR [hazard ratio] = 0.91, 95% CI [confidence interval] = 0.69 to 1.19) or between >32-mm and 32-mm sizes (HR = 1.05, 95% CI = 0.70 to 1.55). The results of our study provide relevant data to orthopaedic surgeons deciding on the use of a larger articulation in a metal-on-polyethylene bearing. A larger head diameter should not be considered a detriment to device survival when an HXLPE liner is used. However, efforts to force the use of a large-size implant appear unsupported, as similar survivorship was observed for all head diameter groups.

Trends in Total Knee Arthroplasty Implant Utilization

The incidence of total knee arthroplasty (TKA) has increased alongside our knowledge of knee physiology, kinematics, and technology resulting in an evolution of TKA implants. This study examines the trends in TKA implant utilization. Data was extracted from The Orthopedic Research Network to evaluate trends in level of constraint, fixed vs. mobile bearing, fixation, and type of polyethylene in primary TKAs. In 2012, 88% used cemented femoral and tibial implants, and 96% involved patellar resurfacing. 38% of implants were cruciate retaining, 53% posterior stabilized or condylar stabilized, 3% constrained. 91% were fixed-bearing, 7% mobile-bearing. 52% of tibial inserts were HXLPE. TKA implant trends demonstrate a preference for cemented femoral and tibial components, patellar resurfacing, fixed-bearing constructs, metal-backed tibial components, patellar resurfacing, and increased usage of HXLPE liners.

Total hip replacement using a highly crosslinked polyethylene liner in Asians with small acetabulum.

To evaluate the medium-term outcomes of total hip replacement (THR) using a thin highly cross-linked polyethylene (HXLPE) liner in an Asian population. Medical records of 20 men and 44 women aged 26 to 80 (mean, 59) years who underwent 80 THRs using a thin HXLPE liner by a single surgeon were reviewed. Indications for THR included dysplasia (n = 26), avascular necrosis (n=26), osteoarthritis (n = 22), rheumatoid arthritis (n = 4), and ankylosing spondylitis (n = 2). The surgical technique, implant used, and rehabilitation protocol were standardised. Radiographs were evaluated for cup migration and peri-implant radiolucency. Femoral head penetration was assessed at day 1 and last follow-up using the Kang modification of the Dorr and Wan method and the PowerPoint method. After a mean follow-up of 7.5 (range, 5.0-11.9) years, no patient had undergone acetabular revision. Two hips were revised for the femoral stem. Femoral head penetration did not correlate with sex, age at surgery, hip pathology, acetabular inclination angle, cup size, or liner thickness. The maximum femoral head penetration was 0.09 mm/year, which was below the osteolysis threshold of 0.1 mm/year. The mean ± standard deviation femoral head penetration was 0.29 ± 0.12 mm (or 0.04 ± 0.02 mm/year) by the PowerPoint method and 0.17 ± 0.22 mm (or 0.02 ± 0.03 mm/year) by the Kang modification of the Dorr and Wan method. Femoral head penetration correlated with the number of years of follow-up (p = 0.012). The use of a thin HXLPE liner in primary THR for patients with small acetabulum achieved good outcomes after a mean of 7.5 years.

Mechanisms of plastic deformation in highly cross-linked UHMWPE for total hip components—The molecular physics viewpoint

Plastic deformation is an unavoidable event in biomedical polymeric implants for load-bearing application during long-term in-vivo service life, which involves a mass transfer process, irreversible chain motion, and molecular reorganization. Deformation-induced microstructural alterations greatly affect mechanical properties and durability of implant devices. The present research focused on evaluating, from a molecular physics viewpoint, the impact of externally applied strain (or stress) in ultra-high molecular weight polyethylene (UHMWPE) prostheses, subjected to radiation cross-linking and subsequent remelting for application in total hip arthroplasty (THA).Two different types of commercial acetabular liners, which belong to the first-generation highly cross-linked UHMWPE (HXLPE), were investigated by means of confocal/polarized Raman microprobe spectroscopy. The amount of crystalline region and the spatial distribution of molecular chain orientation were quantitatively analyzed according to a combined theory including Raman selection rules for the polyethylene orthorhombic structure and the orientation distribution function (ODF) statistical approach.The structurally important finding was that pronounced recrystallization and molecular reorientation increasingly appeared in the near-surface regions of HXLPE liners with increasing the amount of plastic (compressive) deformation stored in the microstructure. Such molecular rearrangements, occurred in response to external strains, locally increase surface cross-shear (CS) stresses, which in turn trigger microscopic wear processes in HXLPE acetabular liners. Thus, on the basis of the results obtained at the molecular scale, we emphasize here the importance of minimizing the development of irrecoverable deformation strain in order to retain the pristine and intrinsically high wear performance of HXLPE components.

The John Charnley Award: Highly crosslinked polyethylene in total hip arthroplasty decreases long-term wear: a double-blind randomized trial.

The use of highly crosslinked polyethylene (HXLPE) is now commonplace for total hip arthroplasty. Hip simulator studies and short-term in vivo measurements suggest that the wear rate of some types of HXLPE is significantly less than conventional ultrahigh-molecular-weight polyethylene (UHMWPE). However, there are few long-term data to support its use. The aim of this study was to measure the long-term steady-state wear of HXLPE compared with UHMWPE liners in a prospective, double-blind, randomized controlled trial using radiostereometric analysis. Fifty-four patients were randomized to receive hip arthroplasties with either UHMWPE liners or HXLPE liners. Complete followup was available on 39 of these patients (72%). All patients received the same cemented stem and an uncemented acetabular component. Three-dimensional penetration of the head into the socket was determined at 10 years using a radiostereometric analysis system, which has an in vivo accuracy of <0.1 mm. Oxford Hip Scores were compared between the groups. At 10 years there was significantly less wear of HXLPE (0.003 mm/year; 95% confidence interval [CI], ±0.010; SD 0.023; range, -0.057 to 0.074) compared with UHMWPE (0.030 mm/year; 95% CI, ±0.012; p<0.001; SD 0.0.27; range, -0.001 to 0.164). The volumetric penetration from 1 to 10 years for the UHMWPE group was 98 mm3 (95% CI, ±46 mm3; SD 102 mm3; range, -4 to 430 mm3) compared with 14 mm3 (95% CI, ±40 mm3; SD 91 mm3; range, -189 to 242 mm3) for the HXLPE group (p=0.01). This study demonstrates that HXLPE has little detectable steady-state in vivo wear. This may result in fewer reoperations from loosening; however, careful clinical followup into the second decade still needs to be performed. Level I, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Clinical and radiographic outcomes of total hip replacement with poly(2-methacryloyloxyethyl phosphorylcholine)-grafted highly cross-linked polyethylene liners: Three-year results of a prospective consecutive series

Objectives. This study aimed to evaluate the clinical safety and wear-resistance of the novel highly cross-linked polyethylene (HXLPE) acetabular liner with surface grafting of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) at 3 years after total hip replacement (THR).Methods. Eighty consecutive patients underwent cementless THR using a 26-mm diameter cobalt–chromium–molybdenum alloy femoral head and a PMPC-grafted HXLPE liner for the bearing couplings. We evaluated the clinical and radiographic outcomes of 76 patients at 3 years after the index surgery.Results. The clinical results at 3 years were equivalent to a Harris hip score of 95.6 points. No adverse events were associated with the implanted PMPC-grafted HXLPE liner, and no periprosthetic osteolysis was detected. The mean femoral head penetration rate was 0.002 mm/year, representing marked reduction compared with other HXLPE liners.Conclusions. A PMPC-grafted HXLPE liner is a safe option in THR and probably reduces the generation of wear particles.

Vitamin-E blended and infused highly cross-linked polyethylene for total hip arthroplasty: A comparison of three-dimensional crystalline morphology and strain recovery behavior

Vitamin-E (α-tocopherol) is now recognized worldwide as one of the most promising antioxidant agents for highly cross-linked polyethylene (HXLPE) used in total joint replacements. In the contemporary manufacturing processes, two alternative methods are currently accepted to incorporate this antioxidant into polyethylene microstructure: (i) blending vitamin-E before consolidation and radiation crosslinking; (ii) infusing vitamin-E via a homogenizing heat treatment after radiation crosslinking. However, the effects of these technological differences on crystalline morphology and mechanical behavior of polyethylene remains to be fully elucidated. The aim of this paper is to quantitatively evaluate the microstructural differences of commercially available vitamin-E blended and infused HXLPE liner (referred to as Liner BL and IF, respectively). For this purpose, confocal/polarized Raman spectroscopy was used to systematically examine the three-phase percentages (amorphous (αa), crystalline (αc), and intermediate third phase (αt)), preferential molecular orientation (θp), and degree of crystalline anisotropy (〈P2(cosβ)〉). Additionally, we compared the time-dependent deformation of Liner BL and IF as obtained by uniaxial stress relaxation tests followed by strain recovery. Distinctive features of the near-surface αc, θp, and〈P2(cosβ)〉 were clearly observed within the first 35μm in the two studied liners. Despite the equivalent level of the bulk αc and 〈P2(cosβ)〉, higher restoring force against a uniaxial strain was observed in Liner IF, which reflects a higher crosslink density in its amorphous phase. On the other hands, a higher degree of surface orientational randomness was detected in Liner BL, which is structurally more beneficial for minimizing the in-vivo occurrence of strain-softening-assisted wear.

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.

History and systematic review of wear and osteolysis outcomes for first-generation highly crosslinked polyethylene.

Highly crosslinked polyethylene (HXLPE) was introduced to reduce wear and osteolysis in total joint arthroplasty. While many studies report wear and osteolysis associated with HXLPE, analytical techniques, clinical study design and followup, HXLPE formulation and implant design characteristics, and patient populations differ substantially among investigations, complicating a unified perspective. Literature on first-generation HXLPE was summarized. We systematically reviewed the radiographic wear data and incidence of osteolysis for HXLPE in hip and knee arthroplasty. PubMed identified 391 studies; 28 met inclusion criteria for a weighted-averages analysis of two-dimensional femoral head penetration rates. To determine the incidence of osteolysis, we estimated a pooled odds ratio using a random-effects model. Weighted-averages analyses of femoral head penetration rates in HXLPE liners and conventional UHMWPE liners resulted, respectively, in a mean two-dimensional linear penetration rate of 0.042 mm/year based on 28 studies (n=1503 hips) and 0.137 mm/year based on 18 studies (n=695 hips). The pooled odds ratio for the risk of osteolysis in HXLPE versus conventional liners was 0.13 (95% confidence interval, 0.06-0.27) among studies with minimum 5-year followup. We identified two clinical studies of HXLPE in TKA, preventing systematic analysis of outcomes. HXLPE liner studies consistently report lower femoral head penetration and an 87% lower risk of osteolysis. Reduction in femoral head penetration or osteolysis risk is not established for large-diameter (>32 mm) metallic femoral heads or ceramic femoral heads of any size. Few studies document the clinical performance of HXLPE in knees.

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.

Comparison of Steady State Femoral Head Penetration Rates Between Two Highly Cross-Linked Polyethylenes in Total Hip Arthroplasty

Given that the manufacture of highly cross-linked polyethylene (HXLPE) is not standardized, the behavior of these materials may vary. Our study compares minimum 5-year steady state femoral head penetration rates using the Martell method, in 2 HXPLEs produced by different manufacturers. Patients received a primary hip arthroplasty using an uncemented acetabular component with an HXLPE liner and a 28-mm femoral head. Forty-seven patients in group A received an HXLPE liner (Reflection XLPE, Smith and Nephew Inc, Memphis, Tenn), and 36 patients in group B received a different HXLPE liner (Longevity, Zimmer Inc, Warsaw, Ind). Average follow-up was 6.42 years in group A and 7.64 years in group B. The steady state head penetration rates were not significantly ( P > .05) different between the HXPLE groups over the midterm with 0.026 mm/y and 0.025 mm/y in groups A and B, respectively.