title: Biomechanical analysis of supracondylar femoral fractures fixed with modern retrograde intramedullary nails.
abstract: OBJECTIVE
  Several new retrograde supracondylar intramedullary nails have been developed to specifically address fractures of the distal femur. The nails appear clinically effective, but there are few biomechanical data documenting the stability of the fixation or the mechanical stiffness of the different designs. The goal of this study was to assess the torsional and bending stiffness of four designs of intramedullary nails developed for this application.
  
  
  METHODS
  Four nail designs were tested in torsion and bending to determine system stiffness: Ace supracondylar, Richards "five hole" and "multi-hole" supracondylar, and Biomet retrograde. The nails were inserted into cadaveric femurs in which a one-centimeter distraction osteotomy had been created seven centimeters proximal to the condyles. The constructs were then tested on an Instron biaxial testing system.
  
  
  RESULTS
  There were no statistically significant differences in bending stiffness among the groups of nails (range 0.79 to 1.18 newtons/meter; p > 0.1). However, the Ace nails (1.10 newtonmeters/degree) did exhibit a statistically lower torsional stiffness compared with the other nails (2.20 to 2.21 newton-meters/ degree; p < 0. 1). No differences were noted as a function of the number of locking holes.
  
  
  CONCLUSIONS
  The bending stiffness of four currently available designs of retrograde intramedullary nails does not appear to be dependent on design variations. The torsional stiffness did vary among the four designs, but this was not determined by the number of fixation holes provided. It appears that a well-placed retrograde supracondylar nail of modern design should have sufficient stiffness to support the femur and provide stability during fracture healing.
authors.affiliation: Department of Orthopaedic Surgery and Bioengineering Center, Wayne State University, Detroit, Michigan, USA.
authors.forename: N
authors.initials: N
authors.lastname: Hora
authors.forename: D C
authors.initials: DC
authors.lastname: Markel
authors.forename: A
authors.initials: A
authors.lastname: Haynes
authors.forename: M J
authors.initials: MJ
authors.lastname: Grimm
mesh_terms: D001696:Biomechanical Phenomena; D001858:Bone Nails; D004867:Equipment Design; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery*; D005594:Fracture Fixation, Intramedullary; D006801:Humans; D008422:Materials Testing