title: In vivo evaluation of edge-loading in metal-on-metal hip resurfacing patients with pseudotumours.
abstract: OBJECTIVE
  Pseudotumours (abnormal peri-prosthetic soft-tissue reactions) following metal-on-metal hip resurfacing arthroplasty (MoMHRA) have been associated with elevated metal ion levels, suggesting that excessive wear may occur due to edge-loading of these MoM implants. This study aimed to quantify in vivo edge-loading in MoMHRA patients with and without pseudotumours during functional activities.
  
  
  METHODS
  The duration and magnitude of edge-loading in vivo was quantified during functional activities by combining the dynamic hip joint segment contact force calculated from the three-dimensional (3D) motion analysis system with the 3D reconstruction of orientation of the acetabular component and each patient's specific hip joint centre, based on CT scans.
  
  
  RESULTS
  Edge-loading in the hips with pseudotumours occurred with a four-fold increase in duration and magnitude of force compared with the hips without pseudotumours (p = 0.02).
  
  
  CONCLUSIONS
  The study provides the first in vivo evidence to support that edge-loading is an important mechanism that leads to localised excessive wear (edge-wear), with subsequent elevation of metal ion levels in MoMHRA patients with pseudotumours.
authors.affiliation: Department of Orthopaedic Surgery, Massachusetts General Hospital, Harvard Medical School, 55 Fruit Street, Suite 3B, Boston, Massachusetts 02114, USA.
authors.forename: Y-M
authors.initials: YM
authors.lastname: Kwon
authors.forename: S J
authors.initials: SJ
authors.lastname: Mellon
authors.forename: P
authors.initials: P
authors.lastname: Monk
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
authors.forename: H S
authors.initials: HS
authors.lastname: Gill
keywords: Edge-loading; Hip resurfacing; In vivo evaluation; Metal ions; Metal-on-metal; Pseudotumours