title: The primary stability of the hip transposition type IIb: a biomechanical in vitro study.
abstract: BACKGROUND
  The hip transposition is firmly established in pelvic sarcoma surgery. However, the primary stability of the hip transposition has not been tested yet so that the mobilisation, respectively the immobilisation of the patient so far solely relied on the experience of the surgeon. The aim of this study was to test the primary stability reliably with the help of a model and to reveal possible differences in stability between currently used anchor systems (TwinFix 6.5 and MITEK SuperAnchor).
  
  
  METHODS
  A biomechanical model of porcine sacra was developed to document the maximum load capacity (load to failure test) and the performance under cyclic load (100 N, 200 N, 350 N, 700 N, 1400 N, each with 1000 cycles), 28 sacra were tested in total. Macroscopic damages, displacement, yield load, stiffness and F(max) were recorded as well.
  
  
  RESULTS
  The load to failure test results showed a 3.9 times higher maximum load capacity for the TwinFix 6.5 anchor (1307 N) compared to the MITEK SuperAnchor (334N). The cyclical test revealed that nearly all MITEK SuperAnchors failed at a load of 350 N. In contrast, the TwinFix 6.5 anchors resisted 4000 cycles up to a load of 1400 N.
  
  
  CONCLUSIONS
  The TwinFix 6.5 anchor proved to be clearly superior to the MITEK SuperAnchor, resulting in the adjustment of the reconstruction technique. Therefore, the immobilisation period of a patient after a hip transposition type IIb could be shortened according to the results of the primary stability test.
authors.affiliation: Department of Orthopaedic Surgery, University Hospital Muenster, Albert-Schweitzer-Str. 33, D-48149 Muenster, Germany. wessling@uni-muenster.de
authors.forename: Martin
authors.initials: M
authors.lastname: Wessling
authors.forename: Mirko
authors.initials: M
authors.lastname: Aach
authors.forename: Mirko
authors.initials: M
authors.lastname: Herbort
authors.forename: Georg
authors.initials: G
authors.lastname: Gosheger
authors.forename: Jendrik
authors.initials: J
authors.lastname: Hardes
authors.forename: Carsten
authors.initials: C
authors.lastname: Gebert
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D001842:Bone and Bones / Q000503:physiopathology*; D004867:Equipment Design; D006615:Hip / Q000503:physiopathology*; D006622:Hip Prosthesis; D066298:In Vitro Techniques; D008422:Materials Testing; D011474:Prosthesis Design; D015203:Reproducibility of Results; D013314:Stress, Mechanical; D013552:Swine; D013718:Tensile Strength; D016474:Weight-Bearing