title: Implant Material, Type of Fixation at the Shaft, and Position of Plate Modify Biomechanics of Distal Femur Plate Osteosynthesis.
abstract: OBJECTIVE
  To investigate whether (1) the type of fixation at the shaft (hybrid vs. locking), (2) the position of the plate (offset vs. contact) and (3) the implant material has a significant effect on (a) construct stiffness and (b) fatigue life in a distal femur extraarticular comminuted fracture model using the same design of distal femur periarticular locking plate.
  
  
  METHODS
  An extraarticular severely comminuted distal femoral fracture pattern (OTA/AO 33-A3) was simulated using artificial bone substitutes. Ten-hole distal lateral femur locking plates were used for fixation per the recommended surgical technique. At the distal metaphyseal fragment, all possible locking screws were placed. For the proximal diaphyseal fragment, different types of screws were used to create 4 different fixation constructs: (1) stainless steel hybrid (SSH), (2) stainless steel locked (SSL), (3) titanium locked (TiL), and (4) stainless steel locked with 5-mm offset at the diaphysis (SSLO). Six specimens of each construct configuration were tested. First, each specimen was nondestructively loaded axially to determine the stiffness. Then, each specimen was cyclically loaded with increasing load levels until failure.
  
  
  RESULTS
  Construct Stiffness: The fixation construct with a stainless steel plate and hybrid fixation (SSH) had the highest stiffness followed by the construct with a stainless steel plate and locking screws (SSL) and were not statistically different from each other. Offset placement (SSLO) and using a titanium implant (TiL) significantly reduced construct stiffness. Fatigue Failure: The stainless steel with hybrid fixation group (SSH) withstood the most number of cycles to failure and higher loads, followed by the stainless steel plate and locking screw group (SSL), stainless steel plate with locking screws and offset group (SSLO), and the titanium plate and locking screws group (TiL) consecutively. Offset placement (SSLO) as well as using a titanium implant (TiL) reduced cycles to failure.
  
  
  CONCLUSIONS
  Using the same plate design, the study showed that implant material, screw type, and position of the plate affect the construct stiffness and fatigue life of the fixation construct. With this knowledge, the surgeon can decide the optimal construct based on a given fracture pattern, bone strength, and reduction quality.
authors.affiliation: *Department of Orthopedic Surgery, University of California, San Francisco, San Francisco, CA; †Institute of Biomechanics, Paracelsus Medical University, Salzburg, Austria; ‡Institute of Biomechanics, Berufsgenossenschaftliche Unfallklinik, Murnau, Germany; §Stryker, Selzach, Switzerland; ‖Stryker, Kiel, Germany; and ¶Department of Trauma Orthopaedic Surgery, Krankenhaus der Barmherzigen Schwestern Ried, Ried im Innkreis, Austria.
authors.forename: Utku
authors.initials: U
authors.lastname: Kandemir
authors.forename: Peter
authors.initials: P
authors.lastname: Augat
authors.forename: Stefanie
authors.initials: S
authors.lastname: Konowalczyk
authors.forename: Felix
authors.initials: F
authors.lastname: Wipf
authors.forename: Geert
authors.initials: G
authors.lastname: von Oldenburg
authors.forename: Ulf
authors.initials: U
authors.lastname: Schmidt
mesh_terms: D001696:Biomechanical Phenomena; D001860:Bone Plates; D005264:Femoral Fractures / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D018460:Fractures, Comminuted / Q000601:surgery; D006801:Humans; D008422:Materials Testing / Q000379:methods*; D012680:Sensitivity and Specificity; D000066908:Simulation Training; D013193:Stainless Steel; D013314:Stress, Mechanical; D014025:Titanium
chemical_list: D013193:Stainless Steel; D014025:Titanium