The Impact of Free Radical Stabilization Techniques on in vivo Mechanical Changes in Highly Cross-Linked Polyethylene Acetabular Liners

Abstract

Michael Decker,1 Amber Price,1 Aria Khalili,2 Robert Klassen,2 Mary Jane Walzak,3 Matthew Teeter,4– 7 Richard McCalden,8 Brent Lanting8 1Department of Orthopaedic Surgery, The University of New Mexico Health Sciences Center, University of New Mexico, Albuquerque, NM, USA; 2Department of Mechanical and Materials Engineering, Western University, London, Ontario, Canada; 3Surface Science Western, University of Western Ontario, London, Ontario, Canada; 4Department of Medical Biophysics, Schulich School of Medicine and Dentistry; 5Imaging Research Laboratories, Robarts Research Institute, Schulich School of Medicine and Dentistry; 6Surgical Innovation Program, Lawson Health Research Institute; 7Division of Orthopaedic Surgery, Schulich School of Medicine and Dentistry, Western University and London Health Sciences Centre, London, Ontario, Canada; 8Division of Orthopaedic Surgery, London Health Sciences Centre, University Hospital, London, Ontario, CanadaCorrespondence: Amber PriceDepartment of Orthopaedics, The University of New Mexico, Albuquerque, NM, 87131-0001, USATel [phone]Fax [phone]Email [email protected]: Numerous thermal free radical stabilization techniques are used in the production of highly cross-linked polyethylene (HXLPE) to improve oxidative stability. Little knowledge exists on the effects of in vivo time on the mechanical properties of HXLPE. The purpose of this study was to determine if free radical stabilization of HXLPE impacts mechanical properties as well as oxidative stability of acetabular liner rims after extended in vivo time.Methods: Retrieved and control remelted, single annealed and sequentially annealed HXLPE liner rims were tested for mechanical properties. Oxidation was measured with FTIR spectroscopy and crystalline phase composition measured with Raman spectroscopy.Results: No correlation was found between in vivo, ex vivo time and hardness for annealed groups. A statistically significant difference in hardness was identified between free radical stabilization groups. No correlation between maximum rim oxidation and in vivo time was found. Detectable levels of rim oxidation were present in 100% of single annealed, 75% of sequentially annealed, and 25% of remelted retrieved liners. Single and sequentially annealed liners demonstrated oxidation and increased crystallinity. Rim mechanical properties change in vivo for implant types. With in vivo time, retrieved remelted HXLPE demonstrated decreased mechanical properties, whereas retrieved single and sequentially annealed HXLPE properties remained stable. All liner cohorts demonstrated evidence of rim oxidation. Subsequent changes in crystallinity were only observed in oxidized annealed liners.Conclusion: HXLPE acetabular liner rims show evidence of in vivo mechanical property degradation, notably in remelted HXLPE, which may be a risk factor in rim fracture and catastrophic implant failure.Keywords: hip, arthroplasty, free radical, polyethylene, mechanical properties

Keywords

• hip
• arthroplasty
• free radical
• polyethylene
• mechanical properties