title: Primary stability of two uncementedacetabular components of different geometry: hemispherical or peripherallyenhanced?
abstract: OBJECTIVE
  This study compared the primary stability of two commercially available acetabular components from the same manufacturer, which differ only in geometry; a hemispherical and a peripherally enhanced design (peripheral self-locking (PSL)). The objective was to determine whether altered geometry resulted in better primary stability.
  
  
  METHODS
  Acetabular components were seated with 0.8 mm to 2 mm interference fits in reamed polyethylene bone substrate of two different densities (0.22 g/cm(3) and 0.45 g/cm(3)). The primary stability of each component design was investigated by measuring the peak failure load during uniaxial pull-out and tangential lever-out tests.
  
  
  RESULTS
  There was no statistically significant difference in seating force (p = 0.104) or primary stability (pull-out p = 0.171, lever-out p = 0.087) of the two components in the low-density substrate. Similarly, in the high-density substrate, there was no statistically significant difference in the peak pull-out force (p = 0.154) or lever-out moment (p = 0.574) between the designs. However, the PSL component required a significantly higher seating force than the hemispherical cup in the high-density bone analogue (p = 0.006).
  
  
  CONCLUSIONS
  Higher seating forces associated with the PSL design may result in inadequate seating and increased risk of component malpositioning or acetabular fracture in the intra-operative setting in high-density bone stock. Our results, if translated clinically, suggest that a purely hemispherical geometry may have an advantage over a peripherally enhanced geometry in high density bone stock. Cite this article: Bone Joint Res 2013;2:264-9.
authors: Golden Jubilee National Hospital, Departmentof Orthopaedics, Agamemnon Street, Clydebank, WestDunbartonshire G81 4DY, UK.
authors: G
authors: G
authors: Antoniades
authors: E J
authors: EJ
authors: Smith
authors: A H
authors: AH
authors: Deakin
authors: S C
authors: SC
authors: Wearing
authors: M
authors: M
authors: Sarungi
keywords: Acetabular cup; Geometry; Peripherally enhanced; Primary stability; THR; Uncemented