Relationship between product demand, tibial polyethylene insert shelf age, and total knee arthroplasty survival: retrospective review of total knees of one design

Shelf aging of gamma-irradiated-in-air polyethylene tibial components has been associated with increased articular surface wear and an elevated risk for revision. Nine hundred fifty cruciate-retaining inserts of one design were implanted between 1987 and 1996 (shelf age, 1.0 +/- 1.2 years). Less frequently used inserts (smallest/largest sizes, thicker thicknesses, supplemental articular constraint) had longer shelf ages (means ranged from 1.2 to 2.6 years). Survival analysis showed that shelf age (P < .01) and gamma-sterilization in air (P = .01) elevated the risk for revision. Surgeons must remain attentive to identify the shelf-aged gamma-irradiated-in-air polyethylene tibial component while following designs from the era when this sterilization method was used. Recognition is expedited by understanding how shelf life is related to product demand and can be of aid when diagnosing the painful knee.     

The pros and cons of polyethylene sterilization with gamma irradiation

This retrospective study evaluated the implant, patient and surgical factors associated with polyethylene wear for one type of porous-coated hemispheric total hip arthroplasty cup. Radiographic wear measurements among 567 Duraloc cups (512 patients) revealed that liners sterilized by gamma-irradiation wore 0.085 mm/year less than those that were sterilized by gas-plasma, a noncross-linking chemical surface treatment. The substantially decreased wear rate associated with gamma-irradiation was attributed to sterilization-induced polyethylene cross-linking. Shelf-aging adversely affected liners that were gamma irradiated in air. On average, highly crystalline Hylamer liners showed a 0.064 mm/year increase in wear rates for each year of shelf storage after terminal sterilization with gamma-irradiation in air. Among conventional Enduron liners, the effect of shelf aging after gamma-irradiation in air was more modest, increasing wear rates by 0.014 mm/year for each year of shelf storage. Because Hylamer's wear performance degraded at about five times the rate of Enduron's, the improved wear resistance associated with gamma-irradiation in air would be lost after 1.3 years of shelf aging for Hylamer compared with 6.1 years for Enduron. For every additional year of age at the time of surgery, the wear rate decreased by 0.003 mm/year. Increased body mass index, a preoperative diagnosis of inflammatory arthritis, and a ceramic femoral head also were associated with decreased wear rates.     

Increased volumetric wear of polyethylene liners with more than 3 years of shelf-life time

We analyzed 20 retrieved gamma-sterilized polyethylene liners (Biomet Hexloc). The long-term durability varied significantly depending on shelf-life time before implantation. Liners with a shelf-life time of 3 years or more evinced significantly ( P 0.002) higher volumetric wear than those with a shelf life time less than 3 years. Infrared spectroscopy and scanning calorimetry showed that all explanted implants underwent substantial in vivo oxidation and crystallization. The oxidative ageing of polyethylene renders the polyethylene liner susceptible to severe wear. Scanning electron microscopy of the bearing surface of the liner revealed abrasive wear as a dominant mechanism. Moreover, poor acetabular design produces excessively thin liners, substandard locking mechanism, and backside wear of the liner. The primary reason for severe wear in the Hexloc liner was poor modular design and oxidative degradation of the polyethylene.     

Factors contributing to rapid wear and osteolysis in hips with modular acetabular bearings made of hylamer

There have been several reports of osteolysis associated with rapid wear of Hylamer. A detailed analysis of retrieved implants and tissues can identify factors contributing to rapid wear and osteolysis. The mean linear wear rate of 12 liners was 0.49 mm/y, and 11 of 12 hips had progressive retroacetabular osteolysis. The average patient age was 50 years, and the mean implantation time was 50 months. All liners were sterilized by gamma irradiation in air. There was an 11-month difference in the average shelf-life of the 3 liners that were white and those that were darker in color. The volumetric wear rate of the white liners was 30% less than that of the others, suggesting a difference in the wear resistance of the liners as a function of shelf life. The mean average surface roughness (Ra) and the mean maximum surface roughness (R(max)) of the femoral heads were increased 3-fold and 50-fold compared with typical values for unused femoral heads. Evidence of 3-body wear, such as metal particles embedded in the liners, was commonly present. The pattern of backside liner deformation and burnishing was consistent with relative motion between the liner and the shell. In addition to generating Hylamer wear particles, repetitive axial motion between the liner and shell could generate fluid pressure, which transmitted through holes in the acetabular shell could cause or contribute to the development of retroacetabular osteolysis. Hylamer particles of variable shape and size, consistent with generation by several wear modes, were isolated from periprosthetic tissues.     

Hylamer wear rates and shelf life: a clinical correlation

We evaluated the performance of 84 Hylamer polyethylene components and zirconia modular femoral heads which were implanted in a single institution over a 5 year period. Patients were followed up for a mean of 6.2 years. The mean rate of penetration was 0.58 mm/year (0.05-1.0). Lot/batch numbers were available in the clinical case notes of 54 patients. Using the lot/batch numbers, we were able to determine the Hylamer cups' shelf lifes. We found that liners with a shelf life greater than 10 months had a significantly greater linear wear (0.38 mm/year) than those implanted in less than 10 months (0.05 mm/year).     

Midterm radiographic comparison of cementless acetabular shells containing lateralized and nonlateralized liners

This retrospective study assessed the effect of lateralized acetabular inserts on polyethylene wear rates, radiographic loosening, and hip stability. Fifty-six 4-mm lateralized liners and 39 neutral liners were compared at a mean follow-up of 7.1 years. Multivariate regression analysis demonstrated a significant increase of 0.04 mm/y in polyethylene wear rate with use of lateralized liners. However, predictable cementless fixation was obtained without screws in both liner groups with no migration or radiographic signs of loosening observed for any cup. The dislocation rate for hips with lateralized liners (3.6%) was less than that for hip with neutral liners (10.3%), although the difference was not significant with the numbers available. Despite the increase in wear rate, hips with lateralized liners performed as well as those with neutral liners with regard to loosening and stability.     

Up to 18-Year Follow-Up Wear Analysis of a First-Generation Highly Cross-Linked Polyethylene in Primary Total Hip Arthroplasty

Background

The advent of highly cross-linked polyethylene (HCLPE) has significantly improved total hip arthroplasty survivorship. HCLPE has been shown to improve wear properties in midterm outcomes when compared to traditional polyethylene liners; however, there is a paucity of studies evaluating long-term outcomes. In addition, there is concern that wear rates may accelerate as the implant ages. Thus, the aims of this study are to report on the longest-to-date follow-up of a specific first-generation HCLPE liner and to determine whether there is a change in the annual wear rate over time.

Polyethylene sterilized without irradiation in a polished uncemented acetabular component-a clinical and radiographic analysis

Clinical and radiographic analysis of the Reflection uncemented acetabular component was performed. Features of this component include a polished inner shell and ethylene oxide sterilization. Clinical information was available for 158 hips (mean, 4.6 years follow-up). A total of 19 hips have undergone or were recommended revision, 8 for aseptic loosening or wear (5%). Wear analysis was performed for 38 hips with more than 5 years of follow-up (mean, 6.7 years). Osteolysis was present in 20 of these patients. Penetration rate averaged 0.15 mm/y. Patients with uncemented femoral fixation (vs cemented) had a significantly higher penetration rate. Increased volumetric wear was seen with uncemented femoral fixation, thin liners, and ceramic heads. This component demonstrated relatively high penetration and osteolysis rates. Continued surveillance is recommended, particularly for active patients with thin liners.     

Comparing In Vivo Performance of Two Highly Cross-Linked Polyethylene Thermal Treatments: Remelting vs Annealing in Acetabular Liners

BackgroundThe introduction of highly cross-linked polyethylene (HXLPE) acetabular liners has greatly improved the wear performance of metal-on-PE bearing surfaces used in total hip arthroplasty. Changing the sterilization environment and adding thermal treatments, such as remelting or annealing, were introduced to limit on-shelf and in vivo oxidation of cross-linked liners. This study compares the wear properties of the remelted A-CLASS (MicroPort) HXLPE liner to a sequentially annealed HXLPE.MethodsThis retrospective study assessed linear and volumetric wear rates using Martell Hip Analysis Suite, and clinical performance through incidences of revision surgeries. A total of 80 remelted and 53 annealed liners were included in the wear analysis. All hips were reviewed for revisions.ResultsThere were no significant differences in steady-state linear or volumetric wear rates for remelted and annealed liners, 0.01 (?0.07 to 0.14) vs ?0.01 (?0.11 to 0.1) mm/y (P = .28) and ?1.03 (?30.99 to 45.43) vs ?1.31 (?32.23 to 23.70) mm³/y (P = .30), respectively. Both cohorts were below the 0.1 mm/y linear wear threshold. The wear rates for patients with femoral head sizes ≥36 mm were not significantly different than those with 32 and 28 mm femoral head sizes (P = .60). Similarly, wear rates for patients with an excessively vertical acetabular component (>50°) were not significantly different than those with standard acetabular component orientations (P = .97). No hips were revised due to liner-related complications.ConclusionThe wear rates of the A-CLASS remelted HXLPE acetabular liner wear rates were comparable to those of a sequentially annealed HXLPE. Further long-term studies are required to ensure acceptable resistance to fatigue and in vivo oxidation.     

Mechanical Properties,Oxidation, and Clinical Performance of Retrieved Highly Cross-Linked Crossfire Liners After Intermediate-Term Implantation

Sixty Crossfire (Stryker Orthopaedics, Mahwah, NJ) liners were consecutively revised after an average of 2.9 years (range, 0.01-8.0 years) for reasons unrelated to wear or mechanical performance of the polyethylene. Femoral head penetration was measured directly from 42 retrievals implanted for more than 1 year. Penetration rate results (0.04 mm/y, on average; range, 0.00-0.13 mm/y) confirmed decreasing wear rates with longer in vivo times. Overall, we observed oxidation levels at the bearing surface of the 60 liners (0.5, on average; range, 0.1-1.7) comparable to those of nonimplanted liners (0.5, on average; range, 0.3-1.1) and preservation of mechanical properties. We also measured elevated oxidation of the rim (3.4, on average; range, 0.2-8.8) that was correlated with implantation time. Rim surface damage, however, was observed in only 3 (5%) of 60 cases. Retrieval analysis of the 3 rim-damaged liners did not reveal an association between surface damage and the reasons for revision.     

Ten- to Sixteen-Year Follow-Up of Highly Cross-Linked Polyethylene in Total Hip Arthroplasty: What Factors Affect Wear?

BackgroundIncrease in acetabular cup abduction in total hip arthroplasty (THA) using conventional polyethylene is associated with greater linear wear. Whether this relationship holds true for highly crosslinked liners, particularly with long-term follow-up, is still controversial. The effect of liner thickness on wear of highly cross-linked liners also remains to be clarified.This study sought to determine (1) the long-term clinical and radiological performance of highly cross-linked polyethylene in THA and (2) the effect of acetabular component positioning, polyethylene thickness, and patient demographics on wear.MethodsNinety-three THAs using a 28-mm hip ball, single brand of highly cross-linked polyethylene liner, and cementless cup were performed in 87 patients. Clinical outcomes were evaluated using the Harris Hip Score and need for revision surgery. Linear and volumetric wear, presence of osteolysis, and cup abduction angle were assessed.ResultsThe mean age at operation was 51.4 years. The mean duration of follow-up was 12.7 years (10-16 years). Patients aged >50 years had higher rates of linear wear than those aged <50 years (P = .015). Positive correlation was found between cup abduction angle (P = .014) and cup version (P = .035) with a linear wear rate. Thinner liners (≤7 mm) had similar rates of linear and volumetric wear as thicker liners (≥8 mm) (P = .447).ConclusionThis is the only study to demonstrate a positive significant relationship between cup abduction angle and version with linear wear rate in THA with at least 10 years of follow-up. Liner thickness was not found to affect wear rates.     

10-Year Follow-Up Wear Analysis of Marathon Highly Cross-Linked Polyethylene in Primary Total Hip Arthroplasty

Background

Short-term and intermediate-term wear rates for highly cross-linked polyethylene (HCLPE) liners in total hip arthroplasty (THA) are significantly lower than published rates for traditional polyethylene liners. The aim of this study was to report the longest-to-date follow-up of a specific HCLPE liner.

Is the use of thin,highly cross-linked polyethylene liners safe in total hip arthroplasty?

Purpose

Due to the high number of total hip arthroplasties (THA) revised due to instability, the use of large femoral heads to reduce instability is justifiable. It is critical to determine whether or not large femoral heads used in conjunction with thin polyethylene liners lead to increased wear rates, which can lead to osteolysis. Therefore, by using validated wear-analysis software, we evaluated linear wear rates in a consecutive cohort of patients who underwent primary THA with thin polyethylene liners.

Methods

All patients were selected from a consecutive, prospectively collected database of 241 THAs performed at a single institution by two fellowship-trained joint-reconstruction surgeons between July 2007 and June 2011. These patients were 1:1 matched to a cohort of patients who had conventional-thickness polyethylene liners.

Results

No significant differences were observed between linear wear rates of thin or conventional-thickness liners. The Kaplan–Meier survivorship for both cohorts was 100 %, and no cases of polyethylene fracture were observed in either cohort.

Conclusions

Our results suggest that according to a mean follow-up of 4 years, the use of thin liners in THA is promising. Longer follow-up is required to assess whether these outcomes are observed later.

     

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.     

Highly Crosslinked Polyethylene Improves Wear But Not Surface Damage in Retrieved Acetabular Liners

Background

Highly crosslinked polyethylene (XLPE) is believed to demonstrate better wear resistance than conventional polyethylene (CPE) in total hip arthroplasty.

Questions/purposes

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.

Methods

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.

Results

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).

Conclusions

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.

Clinical Relevance

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.     

The impact of storage time on the wear rates of ultrahigh-molecular-weight polyethylene acetabular liners in hip simulators

The aim of the study is to explore the impact of storage time on wear rates. Two groups of acetabular liners with a storage time of 1 and 4 years were tested on 2 hip simulators of the same type. There were 6 liners in each group. Gravimetric analysis was performed every 500 000 cycles for a total of 3 million cycles. The mean wear rate for the group of 4-year-old liners (36.3 mg/million cycles) was significantly higher than that for the 1-year-old group (23.1 mg/million cycles) (P < .05). After the last gravimetric analysis, scanning electron microscopy was used to observe the wear patterns of the bearing surfaces. This study found that wear resistance decreased as storage time increased.     

Polyethylene cross-linking by two different methods reduces acetabular liner wear in a hip joint wear simulator.

Advances in cross-linking have led to the development of wear resistant ultrahigh molecular weight polyethylene for total joint replacement. This study compared wear reduction by two different cross-linking methods as measured in a hip wear simulator. One highly cross-linked polyethylene was treated with 7.5 Mrad gamma irradiation with post-irradiation annealing and a sterilization dose of 2.5 Mrad (10 Gamma), while the other used 9.5 Mrad warm irradiation with 10 MeV electron-beam (9.5 EB). Liners of the same design, made from nominally cross-linked (gamma sterilized) polyethylene were also tested. Gravimetric wear analysis was performed every 500,000 cycles for 5,000,000 cycles. After correcting for weight gain due to water absorption, the nominally cross-linked liners demonstrated mean wear rates of 15.7 (+/-1.7) and 12.5 (+/-1.0) mg/million cycles. Both highly cross-linked polyethylene liners demonstrated significantly less wear than their respective controls (with mean wear rates of 1.5 (+/-1.2) and -1.4 (+/-1.5) mg/million cycles). The 9.5 EB liners gained weight presumably due to increased fluid absorption, in addition to that measured in loaded-soaked control implants. Any wear occurring was therefore assumed to have been more than offset by weight gain. Highly cross-linked polyethylene was significantly more wear resistant than non- or nominally cross-linked polyethylene. The differences in wear rates between the two highly cross-linked polyethylene designs (9.5 EB or 10 Gamma) are probably too small to be clinically significant.     

Fifteen-Year Comparison of Wear and Osteolysis Analysis for Cross-Linked or Conventional Polyethylene in Cementless Total Hip Arthroplasty for Hip Dysplasia—A Retrospective Cohort Study

Background

Cross-linked polyethylene (XLPE) acetabular liners used in cementless total hip arthroplasty (THA) have demonstrated better wear resistance at 10 years compared with conventional polyethylene (CPE) liners. No clinical studies have compared XPLE to CPE liners beyond 10 years.