title: In vitro comparison of frictional torque and torsional resistance of aged conventional gamma-in-nitrogen sterilized polyethylene versus aged highly crosslinked polyethylene articulating against head sizes larger than 32 mm.
abstract: BACKGROUND
  The advent of highly crosslinked polyethylene has allowed the re-evaluation of the use of femoral heads larger than 32 mm for metal-on-polyethylene total hip arthroplasties. However, the effect of larger heads on the frictional torque of highly crosslinked polyethylene is unknown.
  
  
  METHODS
  We performed an in vitro examination of the effect of larger chrome cobalt femoral heads (40 mm diameter) on the frictional torque and torsional resistance of hip articulations on aged liners of polyethylene that were sterilized by gamma rays while in nitrogen, and aged highly crosslinked polyethylene. The frictional torque at the femoral head articulation was usually higher for the highly crosslinked polyethylene than for the conventional polyethylene. The aged conventional liners oxidized considerably, which led to gross failure of the polyethylene at the anti-rotation portion of the rim. The aged crosslinked polyethylene showed no such failures despite the higher frictional torque.
  
  
  CONCLUSIONS
  Our findings suggest that in terms of torsional resistance to fatigue when studied as a device, rather than as an isolated material, under these conditions, aged highly crosslinked polyethylene is preferable to aged conventional polyethylene.
authors.affiliation: Harris Orthopaedic Biomechanics and Biomaterials Laboratory, Department of Orthopaedic Surgery, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
authors.forename: Brian R
authors.initials: BR
authors.lastname: Burroughs
authors.forename: Orhun K
authors.initials: OK
authors.lastname: Muratoglu
authors.forename: Charles R
authors.initials: CR
authors.lastname: Bragdon
authors.forename: Keith K
authors.initials: KK
authors.lastname: Wannomae
authors.forename: Steven
authors.initials: S
authors.lastname: Christensen
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Lozynsky
authors.forename: William H
authors.initials: WH
authors.lastname: Harris
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods; D001696:Biomechanical Phenomena; D003432:Cross-Linking Reagents; D005270:Femur Head; D017276:Friction; D006622:Hip Prosthesis / Q000009:adverse effects; D006801:Humans; D066298:In Vitro Techniques; D008422:Materials Testing; D011095:Polyethylenes; D011474:Prosthesis Design; D011475:Prosthesis Failure; D013499:Surface Properties; D013997:Time Factors; D014102:Torsion Abnormality
chemical_list: D003432:Cross-Linking Reagents; D011095:Polyethylenes