title: Importance of a distal centralizer in experimental malpositioning of cemented stems. A biomechanical study on human femora.
abstract: BACKGROUND
  Femoral centralizers in total hip arthroplasty (THA) are designed to improve the neutral implant position and ensure a homogeneous cement mantle without implant-bone impingement. To date there are no data about the cement mantle configuration and implant position after malinsertion, as seen in mini-open approaches or adipose patients with a limited view. The present biomechanical study was performed to investigate whether a distal centralizer may correct and optimize the position of a malinserted femoral stem.
  
  
  METHODS
  Thirteen MS 30 stems with and without a distal centralizer each were implanted in paired fresh human femora. Malinsertion was performed using a 3D guiding device with 10° deviation to the femoral axis in the sagittal plane. The thickness of the cement mantle was measured on the anterior, posterior, medial and lateral side of the implanted stem at a distance of 1 cm each. For each side data were taken at 13 points.
  
  
  RESULTS
  Digital evaluation of the cement mantle thickness revealed compareable values in frontal plane when a centralizer was used (p > 0.4). In contrast the cement mantle thicknesses without a centralizing device varied in the distal region between 3.38 mm and 5.09 mm (p ≤ 0.001) and in the central region between 3.52 mm and 4.19 mm (p ≤ 0.009).
  
  
  CONCLUSIONS
  A distal centralizer allows a more uniform cement mantle and neutral alignment even with a malinsertion of the femoral stem. This could reduce the failure rate and early loosening in complex THA.
authors.affiliation: Department of Orthopaedic Surgery, University Medical Center Rostock, Rostock, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kusserow
authors.affiliation: Department of Orthopedics, Ludwig Maximilians University Munich, Munich, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Ficklscherer
authors.affiliation: Department of Orthopaedic Surgery, University Medical Center Rostock, Rostock, Germany.
authors.forename: Peter Cornelius
authors.initials: PC
authors.lastname: Kreuz
authors.affiliation: Department of Orthopaedic Surgery, University Medical Center Rostock, Rostock, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Finze
authors.affiliation: Department of Orthopaedic Surgery, University Medical Center Rostock, Rostock, Germany.
authors.forename: Wolfram
authors.initials: W
authors.lastname: Mittelmeier
authors.affiliation: Department of Orthopedics, Ludwig Maximilians University Munich, Munich, Germany.
authors.forename: Volkmar
authors.initials: V
authors.lastname: Jansson
authors.affiliation: Department of Anatomy II, Ludwig Maximilians University Munich, Munich, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Milz
authors.affiliation: Department of Orthopedics, Ludwig Maximilians University Munich, Munich, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Wegener
keywords: biomechanical study; cement mantle; distal centralizer; femoral stem; hip arthroplasty