title: Biomechanical evaluation of different offset versions of a cementless hip prosthesis by 3-dimensional measurement of micromotions.
abstract: BACKGROUND
  Cementless hip prostheses with different offsets are frequently used to restore the rotation center of the hip. However, a rising offset is theoretically associated with a potential risk for increased interface stresses and early loosening.
  
  
  METHODS
  To assess this potential risk for cementless stems, the primary stability of the CLS Spotorno stem was examined with respect to three different femoral neck versions (125°, 135° and 145°) measuring 3-dimensional micromotions. For this purpose 18 stems were implanted in composite femurs and tested dynamically using physiological loading conditions considering the necessary adaptation according to the different offsets. Additionally the deformations at the surface of the composite femur were recorded to draw conclusions about the tendency for stress shielding.
  
  
  RESULTS
  The micromotions of the different offset versions were not significantly different. The highest values were obtained at the tip of the stems, even exceeding the critical limit for osseous integration of 150μm. Compared to untreated composite femurs the alteration of the deformations at the surface remained relatively low. A significant difference was only observed in the ventral measurement points.
  
  
  CONCLUSIONS
  According to the measured micromotions no offset version of the CLS Spotorno can be declared as superior. The assumption that the varus version is characterized by extended interface stresses could not be confirmed. Furthermore, it could be demonstrated that according to the principle of proximal load transfer of the CLS Spotorno stem an osseous integration of the distal part cannot be expected and that the risk for stress shielding appears to be relatively low.
authors.affiliation: Department of Orthopaedic Surgery, University Hospital of Munich (LMU), Campus Grosshadern, Germany. andreas.fottner@med.uni-muenchen.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Fottner
authors.forename: Carolin V
authors.initials: CV
authors.lastname: Peter
authors.forename: Florian
authors.initials: F
authors.lastname: Schmidutz
authors.forename: Lorenz
authors.initials: L
authors.lastname: Wanke-Jellinek
authors.forename: Christian
authors.initials: C
authors.lastname: Schröder
authors.forename: Farhad
authors.initials: F
authors.lastname: Mazoochian
authors.forename: Volkmar
authors.initials: V
authors.lastname: Jansson
mesh_terms: D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D001696:Biomechanical Phenomena; D002484:Cementation / Q000379:methods; D004867:Equipment Design; D005269:Femur / Q000473:pathology; D005272:Femur Neck / Q000033:anatomy & histology; D006622:Hip Prosthesis; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D009038:Motion; D016348:Osseointegration; D019736:Prostheses and Implants; D011474:Prosthesis Design / Q000379:methods; D012306:Risk; D013314:Stress, Mechanical; D013696:Temperature