title: Implant material and design alter construct stiffness in distal femur locking plate fixation: a pilot study.
abstract: BACKGROUND
  Construct stiffness affects healing of bones fixed with locking plates. However, variable construct stiffness reported in the literature may be attributable to differing test configurations and direct comparisons may clarify these differences.
  
  
  OBJECTIVE
  We therefore asked whether different distal femur locking plate systems and constructs will lead to different (1) axial and rotational stiffness and (2) fatigue under cyclic loading.
  
  
  METHODS
  We investigated four plate systems for distal femur fixation (AxSOS, LCP, PERI-LOC, POLYAX) of differing designs and materials using bone substitutes in a distal femur fracture model (OTA/AO 33-A3). We created six constructs of each of the four plating systems. Stiffness under static and cyclic loading and fatigue under cyclic loading were measured.
  
  
  RESULTS
  Mean construct stiffness under axial loading was highest for AxSOS (100.8 N/mm) followed by PERI-LOC (80.8 N/mm) and LCP (62.6 N/mm). POLYAX construct stiffness testing showed the lowest stiffness (51.7 N/mm) with 50% stiffness of AxSOS construct testing. Mean construct stiffness under torsional loading was similar in the group of AxSOS and PERI-LOC (3.40 Nm/degree versus 3.15 Nm/degree) and in the group of LCP and POLYAX (2.63 Nm/degree versus 2.56 Nm/degree). The fourth load level of > 75,000 cycles was reached by three of six AxSOS, three of six POLYAX, and two of six PERI-LOC constructs. All others including all LCP constructs failed earlier.
  
  
  CONCLUSIONS
  Implant design and material of new-generation distal femur locking plate systems leads to a wide range of differences in construct stiffness.
  
  
  CONCLUSIONS
  Assuming construct stiffness affects fracture healing, these data may influence surgical decision-making in choosing an implant system.
authors: Department of Trauma Orthopaedic Surgery, Krankenhaus der Barmherzigen Schwestern Ried, Schlossberg 1, 4910, Ried im Innkreis, Austria. ulf.schmidt@bhs.at
authors: Ulf
authors: U
authors: Schmidt
authors: Rainer
authors: R
authors: Penzkofer
authors: Samuel
authors: S
authors: Bachmaier
authors: Peter
authors: P
authors: Augat
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D005264:Femoral Fractures / Q000601:surgery*; D005269:Femur / Q000601:surgery*; D006801:Humans; D008422:Materials Testing; D010865:Pilot Projects