title: Backside Wear Is Not Dependent on the Acetabular Socket Design in Crosslinked Polyethylene Liners.
abstract: BACKGROUND
  Although it is understood that backside damage occurs in polyethylene acetabular liners, the effect of highly crosslinked polyethylene, which has completely replaced conventional polyethylene, has yet to be examined.
  
  
  OBJECTIVE
  The purpose of this study was to answer the following questions: (1) With conventional polyethylene (CPE), did the acetabular design make a difference in backside wear? (2) Is there a difference in backside damage between CPE and crosslinked polyethylene (XLPE) liners? (3) With XLPE, is the difference in backside wear between designs still present? (4) Is there any difference in backside damage in various zones on backside of individual liners?
  
  
  METHODS
  This single-institution retrieval analysis involved visual damage scoring on the backside of 233 polyethylene liners implanted between 2002 and 2011. The liners were retrieved from either polished/dovetail cups (PD) or roughened/wire cups (RW) made by two different manufacturers. The inserts were divided into four groups: PD-CPE (n = 105), PD-XLPE (n = 16), RW-CPE (n = 99), and RW-XLPE (n = 13). Aseptic loosening and polyethylene wear were the predominant reasons for revision of CPE liners, whereas instability and infection were the common reasons for revision of XLPE liners. The time in situ (TIS) was shorter for the XLPE liners as compared with the CPE liners (PD-CPE: 8.5 years [SD 4.4]; RD-CPE: 9.5 [SD 4.8]; PD-CPE: 3.8 [SD 3.7]; RD-XLPE: 4.0 [SD 4.3]). The backside of each liner was divided into five zones and graded initially from a scale of 0 to 3 for seven different damage modes by one observer. There was substantial interobserver (kappa 0.769) and intraobserver (0.736) reliability on repeat scoring. To compare the effects of crosslinking, a subset of the conventional polyethylene liners was matched to the crosslinked liners based on TIS, resulting in 16 per group for the two PD types and 13 per group for the two RW types.
  
  
  RESULTS
  Total damage scores in the RW-CPE (19 ± 7) group were greater (p < 0.001) than the PD-CPE group (8 ± 4). Damage was reduced with XLPE (p = 0.02) only for the RW-XLPE (9 ± 9) versus RW-CPE-type sockets (4 ± 4). There was no difference (p = 0.16) between the RW-XLPE group and the PD-XLPE group. Damage scores in the peripheral zone of the locking mechanisms were higher for RW-CPE (4 ± 3) compared with PD-CPE (1.4 ± 1.0, p < 0.001) and RW-XLPE (1.3 ± 1.3, p = 0.02). Damage was greater (p < 0.001) within the superior zones (7 ± 4) compared with the inferior zones (3.0 ± 2.8) of all liners.
  
  
  CONCLUSIONS
  The current study shows greater backside damage for CPE in the roughened, wire lock cups. XLPE was shown to be more resistant to backside damage for both socket designs.
  
  
  CONCLUSIONS
  Although the polished/dovetail cups seem to cause less backside damage in the CPE liners than roughened/wire cups, the use of XLPE liners has been shown to protect the liner from backside damage in either cup design. If an acetabular shell has a functional locking mechanism, surgeons should not worry about cup design when undertaking isolated liner revision using XLPE liners.
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, 339 Windermere Road, London, Ontario, N6A 5A5, Canada.
authors.forename: Kamal
authors.initials: K
authors.lastname: Bali
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, 339 Windermere Road, London, Ontario, N6A 5A5, Canada.
authors.forename: Richard W
authors.initials: RW
authors.lastname: McCalden
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, 339 Windermere Road, London, Ontario, N6A 5A5, Canada.
authors.forename: Douglas D R
authors.initials: DD
authors.lastname: Naudie
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, 339 Windermere Road, London, Ontario, N6A 5A5, Canada.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: MacDonald
authors.affiliation: Division of Orthopaedic Surgery, Department of Surgery, Schulich School of Medicine & Dentistry, Western University, 339 Windermere Road, London, Ontario, N6A 5A5, Canada. matthew.teeter@lhsc.on.ca.|Department of Medical Biophysics, Schulich School of Medicine & Dentistry, Western University, London, Ontario, Canada. matthew.teeter@lhsc.on.ca.|The Surgical Innovation Program, Lawson Health Research Institute, London, Ontario, Canada. matthew.teeter@lhsc.on.ca.
authors.forename: Matthew G
authors.initials: MG
authors.lastname: Teeter
mesh_terms: D000077:Acetabulum / Q000503:physiopathology / Q000601:surgery*; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D003833:Denture, Partial, Temporary; D020878:Device Removal; D005260:Female; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000601:surgery; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D009864:Ontario; D020959:Polyethylene / Q000737:chemistry*; D011237:Predictive Value of Tests; D011475:Prosthesis Failure; D016459:Prosthesis-Related Infections / Q000382:microbiology / Q000601:surgery; D012086:Reoperation; D015203:Reproducibility of Results; D012307:Risk Factors; D013314:Stress, Mechanical; D013499:Surface Properties; D013997:Time Factors; D016896:Treatment Outcome
chemical_list: D020959:Polyethylene