title: Increasing nail-cortical contact to increase fixation stability and decrease implant strain in antegrade locked nailing of distal femoral fractures: a biomechanical study.
abstract: BACKGROUND
  Proximity of the distal locking screw to the fracture site potentially can cause implant failure in locked nailing of distal femoral fractures. In this biomechanical study, we investigated the effects of nail-cortical contact and nail purchase in the distal subchondral bone on fixation stability and implant strain.
  
  
  METHODS
  Using fiberglass artificial femurs, we fixed five different distal femoral osteotomies with specially manufactured locked nails representing different conditions of nail-cortical contact. In each condition, six femur-nail constructs were loaded on the femoral head axially with 700 N; then we measured the fixation stability and strain at the superiormost distal locking screw and nail hole. The tests were conducted both with and without nail purchase in distal subchondral bone.
  
  
  RESULTS
  When there was no nail-cortical contact, the load transmitted to the distal femoral fragment was completely borne by the nail and the distal locking screws. Low fixation stability and high strain on the distal screw and nail hole resulted. Greater nail-cortical contact increased the fixation stability and decreased strains on the distal screw and nail hole. Purchase of the nail tip in distal subchondral bone significantly increased the fixation stability and decreased nail hole strain except in the situation of long nail-cortical contact. The screw strain was significantly reduced in all conditions, and the reduction in strain was significantly greater than that associated with the nail hole, 32% +/- 8% versus 15.7% +/- 2.5% (p = 0.002).
  
  
  CONCLUSIONS
  In locked nailing of distal femoral fractures, the prime factor determining fixation stability and implant strain is nail-cortical contact. In situations without nail-cortical contact, a longer nail with purchase in the subchondral bone of the distal femur is recommended.
authors.affiliation: Department of Orthopedic Surgery, National Taiwan University Hospital Yun-Lin Branch, Yun-Lin County, Taiwan.
authors.forename: Shier-Chieg
authors.initials: SC
authors.lastname: Huang
authors.forename: Chen-Chiang
authors.initials: CC
authors.lastname: Lin
authors.forename: Jinn
authors.initials: J
authors.lastname: Lin
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D001863:Bone Screws; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods*; D010027:Osteotomy / Q000379:methods; D013193:Stainless Steel; D013314:Stress, Mechanical
chemical_list: D013193:Stainless Steel