title: Fixation pattern of conical and cylindrical modular revision hip stems in different size bone defects.
abstract: OBJECTIVE
  Femoral defects often make it difficult to achieve sufficient fixation of the stem during revision surgery. No clinical studies comparing modular stems are available and differentiated recommendations are rare. The aim of this study was to compare the fixation of different revision stems in an experimental and standardised manner.
  
  
  METHODS
  Segmental AAOS type I and III defects were reproduced in four femur pairs and two modular stems of different shape (cylindrical and conical) were implanted. Interfacial stem-bone movements were measured under axial torque application to analyze the stem fixation depending on defect extension.
  
  
  RESULTS
  Both stems showed adequate fixation in AAOS type I defect. The defect extension significantly reduced the fixation of both implants. The fixation pattern changed significantly for the cylindrical-shaped stem but was maintained for the conical-shaped stem.
  
  
  CONCLUSIONS
  Shape as well as the extension of femoral defect have an impact on primary fixation. A type I defect seems to be bridgeable for both stems albeit in a different way. In contrast, stem-demanding activities during the healing phase have to be avoided for the conical-shaped stem in a type III defect, whereas the cylindrical-shaped stem has already ceased to be sufficiently stable in this case.
authors.affiliation: Laboratory of Biomechanics and Implant Research, Department of Orthopaedics, Traumatology and Paraplegiology, University Hospital Heidelberg, Schlierbacher Landstrasse 200a, 69118, Heidelberg, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kinkel
authors.forename: Jan
authors.initials: J
authors.lastname: Nadorf
authors.forename: Marc N
authors.initials: MN
authors.lastname: Thomsen
authors.forename: Christian
authors.initials: C
authors.lastname: Heisel
authors.forename: Alexander
authors.initials: A
authors.lastname: Jahnke
authors.forename: Jan P
authors.initials: JP
authors.lastname: Kretzer
authors.forename: Eike
authors.initials: E
authors.lastname: Jakubowitz
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D005260:Female; D005269:Femur / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation; D019415:Torque