A novel method of cross-linking ultra-high-molecular-weight polyethylene to improve wear, reduce oxidation, and retain mechanical properties: Recipient of the 1999 HAP Paul Award

doi:10.1054/arth.2001.20540

The Journal of Arthroplasty

Volume 16, Issue 2, February 2001, Pages 149-160

https://doi.org/10.1054/arth.2001.20540 Get rights and content

Abstract

Increasing cross-linking has been shown in vitro and in vivo to improve markedly the wear resistance of ultra-high-molecular-weight polyethylene (UHMWPE). The reduction in the mechanical properties of polyethylene under certain methods used to produce cross-linking has been a concern, however. These reductions are known to result from the processes used to increase the cross-link density and could affect the device performance in vivo. We present a novel method of increasing the cross-link density of UHMWPE in which UHMWPE is irradiated in air at an elevated temperature with a high-dose-rate electron beam and subsequently is melt-annealed. This treatment improves markedly the wear resistance of the polymer as tested in a hip simulator, while maintaining the mechanical properties of the material within national and international standards. This method leads to the absence of detectable free radicals in the polymer and, as a result, excellent resistance to oxidation of the polymer.

Section snippets

Materials and methods

In the present study, various properties of a highly cross-linked UHMWPE were compared with those of conventional (control) UHMWPE. We selected as the control a widely used contemporary form of UHMWPE (ie, gamma sterilized in nitrogen). The cross-linking method and the details of the analytic testing used are described subsequently.

The cross-linking was carried out with cylindric test samples in the form of disks (9 cm in diameter and 4 cm in thickness), which were machined from ram-extruded

Results

Table 1 lists the data on the wear and creep measurements of the WIAM and control liners as tested on the Boston hip simulator.The wear data are presented in Fig. 2 as a comparison of the average weight change of the WIAM cross-linked UHMWPE acetabular liners with that of the control liners for 22- and 28-mm femoral head sizes.

. Graph shows the hip simulator weight change data of WIAM and control UHMWPE liners studied in the hip simulator in Sulzer Interop shells with 28-mm inner and 49-mm outer

Discussion

The 3 most important material properties of UHMWPE for surgical use in acetabular reconstruction are wear resistance, oxidation resistance, and mechanical properties of the material. Any changes in UHMWPE must be examined to ensure that in the effort to obtain increased wear resistance or improved long-term oxidative stability, the mechanical properties are acceptable in terms of device safety.

The wear behavior of the WIAM UHMWPE was studied in the form of an acetabular liner, using simulated

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Isolated Liner Exchange in Total Hip Arthroplasty at a Mean of 13 Years of Follow-up: Does Fixation Technique Matter?
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Data for all patients who had undergone isolated liner exchange surgery in our institution between April 1995 and January 2015 were retrieved. Patients were classified according to the type of polyethylene liner (conventional or highly crosslinked polyethylene) and the locking mechanism used (original locking mechanism or cemented). Survivorship and revision rates were compared among different subgroups. A total of 118 isolated liner exchanges were performed and patients had a mean duration of follow-up of 13 years (range, 5 to 25).
Overall estimated mean survivorship was 17 years. Use of highly crosslinked polyethylene (HXLPE) had a lower re-revision rate compared to conventional liners (10.5 versus 46.9%) (P < .001). The re-revision rate of exchanges using HXLPE was not affected by the type of fixation (original locking mechanism 11.1 versus cement 10.0%, P = .868). Conversely, using the original locking mechanism with a conventional liner had a higher re-revision rate compared to cemented conventional liners (58.3 versus 12.5%) (P = .024).
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At a mean follow-up of 10.4 years (range, 8 to 13.4), the mean linear wear rate was 0.0172 mm/year and the mean volumetric wear rate was 16.99 mm³/year. There were no instances of osteolysis or mechanical failures at any time point and there was a 100% acetabular component survival rate. Younger age and use of offset liners were independent risk factors for increased wear (P < .01 for both).
Our series of a third-generation HXLPE demonstrated very low wear rates and excellent implant survival at a mean of 10.4 years following primary THA. Future comparative studies at the 15- and 20-year follow-up timepoints are necessary to determine if such findings translate to true improvements in the tribological properties and longevity of these liners when compared to previous generations of HXLPE liners.
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Large Femoral Heads in Total Hip Arthroplasty With Vitamin E Highly Cross-Linked Polyethylene: Head Penetration Rates Compared to Highly Cross-Linked Polyethylene
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Highly cross-linked polyethylene with vitamin E (VE-HXLPE) has shown superior tribological properties and has been rapidly adopted in total hip arthroplasty. However, the majority of studies compare VE-HXLPE to conventional or moderately cross-linked polyethylene using standard femoral head sizes. This study's purpose was 2-fold: (1) compare radiographic femoral head penetration (FHP) between VE-HXLPE and HXLPE and (2) evaluate FHP in large femoral heads ≥40 mm.
One hundred forty-two consecutive primary total hip arthroplasties using ceramic femoral heads (n = 84 VE-HXLPE; n = 58 HXLPE) in a single implant system were retrospectively reviewed. FHP was measured radiographically utilizing Martell method at 4-week, 1-year, and latest radiographs. FHP, cup position, and demographic variables were compared between VE-HXLPE and HXLPE liners.
Median linear FHP was lower for VE-HXLPE compared to HXLPE during the initial “bedding-in” period between 4-week and 1-year (0.383 vs 0.551 mm, P = .650) and between 1-year and latest follow-up (0.131 vs 0.270 mm/y, P = .636) although without statistical significance. Acetabular cup inclination and anteversion did not influence linear or volumetric FHP (P ≥ .204). Large femoral heads (≥40 mm) were predictive of higher FHP during the early bedding-in period (P ≤ .025) but did not have an effect beyond 1 year in multivariate regression with numbers available. No radiographic osteolysis was observed in any case.
These findings support others that VE-HXLPE is the optimal polyethylene bearing surface to minimize FHP during the bedding-in period and beyond. Surprisingly, large ceramic femoral heads appear to influence FHP during the initial bedding-in period but do not increase FHP beyond 1 year. Further longer term follow-up remains warranted.
III.

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^*: †Department of Orthopaedic Surgery, Harvard Medical School, Boston, Massachusetts.

^**: This article is the recipient of the 1999 HAP Paul Award.

^*: Funds were received in partial support of the research material described in this article from the William H. Harris Foundation and Sulzer Orthopaedics.

^**: Reprint requests: Orhun K. Muratoglu, PhD, Orthopaedic Biomechanics and Biomaterials Laboratory, Massachusetts General Hospital, GRJ 1206, Boston, MA 02114.

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Original ArticlesA novel method of cross-linking ultra-high-molecular-weight polyethylene to improve wear, reduce oxidation, and retain mechanical properties: Recipient of the 1999 HAP Paul Award*,**,*,**

Abstract

Section snippets

Materials and methods

Results

Discussion

Radiat Phys Chem

Biomaterials

Biomaterials

Biomaterials

Biomaterials

J Biomech

Polymer

J Arthroplasty

Radiat Phys Chem

The problem is osteolysis

Clin Orthop

Osteolysis in alloarthroplasty of the hip: the role of ultra-high molecular weight polyethylene wear particles

Clin Orthop

The radiation improvement of polyethylene prostheses

J Bone Joint Surg Br

Clinical experience with gamma irradiation-crosslinked polyethylene-A 14 to 20 year follow-up report

S Afr Bone Joint Surg

Long term clinical results of THR: clinical results of THR of an alumina head with a cross-linked UHMWPE cup

Orthop Surg Traumatol

Prospective clinical and joint simulator studies of a new total hip arthroplasty using alumina ceramic heads and cross-linked polyethylene cups

J Bone Joint Surg Br

Low-friction arthroplasty of the hip using alumina ceramic and cross-linked polyethylene: a ten-year follow-up report

J Bone Joint Surg Br

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

J Orthop Res

Cross-linking of polythene by pile radiation

Proc Roy Soc Lond A

Crosslinking of ultra-high molecular weight polyethylene in the melt by means of 2.5-dimethyl-2.5-bis(tert-butyldioxy)-3-hexyne: 2. Crystallization behaviour and mechanical properties

Polymer

Original Articles
A novel method of cross-linking ultra-high-molecular-weight polyethylene to improve wear, reduce oxidation, and retain mechanical properties: Recipient of the 1999 HAP Paul Award*,**,*,**