title: Internal fixation of type-C distal femoral fractures in osteoporotic bone: surgical technique.
abstract: BACKGROUND
  Fixation of distal femoral fractures remains a challenge, especially in osteoporotic bone. This study was performed to investigate the biomechanical stability of four different fixation devices for the treatment of comminuted distal femoral fractures in osteoporotic bone.
  
  
  METHODS
  Four fixation devices were investigated biomechanically under torsional and axial loading. Three intramedullary nails, differing in the mechanism of distal locking (with two lateral-to-medial screws in one construct, one screw and one spiral blade in another construct, and four screws [two oblique and two lateral-to-medial with medial nuts] in the third), and one angular stable plate were used. All constructs were tested in an osteoporotic synthetic bone model of an AO/ASIF type 33-C2 fracture. Two nail constructs (the one-screw and spiral blade construct and the four-screw construct) were also compared under axial loading in eight pairs of fresh-frozen human cadaveric femora.
  
  
  RESULTS
  The angular stable plate constructs had significantly higher torsional stiffness than the other constructs; the intramedullary nail with four-screw distal locking achieved nearly comparable results. Furthermore, the four-screw distal locking construct had the greatest torsional strength. Axial stiffness was also the highest for the four-screw distal locking device; the lowest values were achieved with the angular stable plate. The ranking of the constructs for axial cycles to failure was the four-screw locking construct, with the highest number of cycles, followed by the angular stable plate, the spiral blade construct, and two-screw fixation. The findings in the human cadaveric bone were comparable with those in the synthetic bone model. Failure modes under cyclic axial load were comparable for the synthetic and human bone models.
  
  
  CONCLUSIONS
  The findings of this study support the concept that, for intramedullary nails, the kind of distal interlocking pattern affects the stabilization of distal femoral fractures. Four-screw distal locking provides the highest axial stability and nearly comparable torsional stability to that of the angular stable plate; the four-screw distal interlocking construct was found to have the best combined (torsional and axial) biomechanical stability.
authors.affiliation: Department of Traumatology, Hand and Reconstructive Surgery, Friedrich Schiller University Jena, Erlanger Allee 101, D-07747 Jena, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Mückley
authors.forename: Dirk
authors.initials: D
authors.lastname: Wähnert
authors.forename: Konrad L
authors.initials: KL
authors.lastname: Hoffmeier
authors.forename: Geert
authors.initials: G
authors.lastname: von Oldenburg
authors.forename: Rosemarie
authors.initials: R
authors.lastname: Fröber
authors.forename: Gunther O
authors.initials: GO
authors.lastname: Hofmann
mesh_terms: D001860:Bone Plates; D001863:Bone Screws; D002102:Cadaver; D005264:Femoral Fractures / Q000209:etiology / Q000473:pathology / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000379:methods*; D018460:Fractures, Comminuted / Q000209:etiology / Q000473:pathology / Q000601:surgery*; D006801:Humans; D010024:Osteoporosis / Q000150:complications* / Q000473:pathology / Q000601:surgery; D016474:Weight-Bearing