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Highly cross-linked polyethylene shows steady penetration rates, lower wear
Four studies found steady radiographic wear rates with cross-linked polyethylene hip components 7-years to 10-years follow-up.
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Highly cross-linked polyethylene implants have demonstrated excellent radiographic results, minimal penetration and low linear wear, even against large femoral heads, according to a recent presentation that reviewed four critical polyethylene studies in the tribology literature.
“Our conclusions with these four studies — and numerous studies throughout the literature — suggest that first generation highly cross-linked polyethylene (HXLPE) has excellent clinical results at 7 to 10 years,” Harry E. Rubash, MD, orthopedic department chief at Massachusetts General Hospital (MGH), said during his presentation at the SICOT XXV Triennial World Congress 2011 in Prague. Rubash’s co-authors on these studies were Charles Bragdon, PhD; Brian Jarrett, BS; Michael Dornier, MS; Andrew Freiberg, MD; Young-Min Kwon, MD, PhD; Henrik Malchau, MD, PhD; and William H. Harris MD, DSc.
Penetration rate unchanged
Rubash discussed four key polyethylene implant wear studies: a 7-year to 10-year single-center follow-up of penetration rates for HXLPE vs. conventional polyethylene; a 5-year to 10-year follow-up multicenter study of Longevity (Zimmer; Warsaw, Ind.) polyethylene components; a multicenter, radio stereometric analysis (RSA) study of large diameter femoral head total hip arthroplasty and preliminary vitamin E highly cross-linked polyethylene data.
The first investigation revealed no revisions for wear or liner fracture among implants studied, as well as any osteolysis or component loosening, Rubash noted. He and colleagues examined 184 patients postoperatively at the 7-year follow-up and 44 patients at the 10-year follow-up. Analyses done at both time points showed low linear penetration rates using the Martell method for edge detection and wear.
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However, concerns from a Swedish group examining RSA findings led the MGH team to conduct a subsequent study examining radiographs of penetration rates of 278 HXLPE implants used in patients treated at seven centers who were followed up for 5 years to 10 years. The primary implants involved Longevity liners and 26-mm, 28-mm and 32-mm diameter chromium cobalt femoral heads. Rubash and colleagues found no change in the penetration rate.
Linear wear studied
“Our conclusions of these two studies showed that the MGH [study], at least at mid-term follow-up, showed low femoral head penetration rates at 7 to 10 years with no signs of osteolysis by plain films and our multicenter study showed the same,” Rubash said. “We were not able to demonstrate an increase in femoral head penetration rate like they did in the Swedish study with our U.S. multicenter study.”
The third study Rubash cited compared standard size femoral heads (26 mm, 28 mm and 32 mm) to larger femoral heads (36 mm, 28 mm and 40 mm) in 525 patients to determine corresponding linear wear rates. Researchers found no signs of osteolysis and a low linear wear rate for all femoral head sizes, Rubash said.
“The wear of HXLPE is extremely low, even when articulating against femoral head diameters greater than 32 mm,” Rubash said, noting that although researchers observed increases in the wear rate with larger femoral heads, the difference was not statistically significant.
A study of 51 hips in 47 patients examined at the effects of the E1 Antioxidant Infused Technology (Biomet; Warsaw, Ind.) polyethylene implants vs. conventional polyethylene implants. The investigators found penetration with “E1 polyethylene is very, very similar to the cross-linked polyethylene both [with] the 28 mm heads, as well as the 36 mm heads,” Rubash said.
Although HXLPE implants may have a low wear rate, Rubash mentioned some of the other benefits to using polyethylene compared to other hip articulation materials: “With crosslinked polyethylene, you can avoid fractures, squeaking, [aseptic lymphocytic vasculitis-associated lesions] ALVAL, pseudotumors and a variety of other reasons for sleepless nights.” – by Jeff Craven
References:
- Bragdon C, Burke D, Ekeledo A, et al. Seven to ten year follow-up of highly cross-linked polyethylene liners in total hip arthroplasty. J Bone Joint Surg Br. 2010;92:511.
- Digas G, Kärrholm J, Thanner J, Herberts P. 5-year experience of highly cross-linked polyethylene in cemented and uncemented sockets: two randomized studies using radiostereometric analysis. Acta Orthop. 2007;78(6):746-754.
- Rubash HE. International Hip Society Symposium: Bearing couples. Highly cross-linked polyethylene. Presented at the SICOT XXV Triennial World Congress 2011. Sept 6-9. Prague.
- Harry E. Rubash, MD, can be reached at 55 Fruit St., Yawkey Center for Outpatient Care, Suite 3700, Boston, MA 02114; 617-726-5231; email: hrubash@partners.org.
- Disclosure: Rubash receives research support from Biomet and Zimmer.