title: Extra- vs. intramedullary treatment of pertrochanteric fractures: a biomechanical in vitro study comparing dynamic hip screw and intramedullary nail.
abstract: BACKGROUND
  Due to the demographic trend, pertrochanteric fractures of the femur will gain increasing importance in the future. Both extra- and intramedullary implants are used with good results in the treatment of these fractures. New, angular stable extramedullary implants promise increased postoperative stability even with unstable fractures. Additional trochanteric plates are intended to prevent secondary impaction, varisation and shortening of the fracture, as well as medialisation of the femoral shaft. The aim of this study was to perform a biomechanical comparison of both procedures regarding their postoperative stability and failure mechanisms.
  
  
  METHODS
  Twelve fresh-frozen human femurs were randomized into two groups based on the volumetric bone mineral density (vBMD). Standardized pertrochanteric fractures (AO31-A2.3) were generated and treated either with an angular stable dynamic hip screw (DHS) or an intramedullary nail (nail). Correct implant position and the tip-apex distance (TAD) were controlled postoperatively using X-ray. Specimens were mounted in a servohydraulic testing machine and an axial loading was applied according to a single-leg stance model. Both groups were biomechanically compared with regard to native and postoperative stiffness, survival during cyclic testing, load to failure, and failure mechanisms.
  
  
  RESULTS
  TAD, vBMD, and native stiffness were similar for both groups. The stiffness decreased significantly from native to postoperative state in all specimens (p < 0.001). The postoperative stiffness of both groups varied non-significantly (p = 0.275). The failure loads for specimens treated with the nail were significantly higher than for those treated with the DHS (8480.8 ± 1238.9 N vs. 2778.2 ± 196.8 N; p = 0.008).
  
  
  CONCLUSIONS
  Extra- and intramedullary osteosynthesis showed comparable results as regards postoperative stiffness and survival during cyclic testing. Since the failure load of the nail was significantly higher in the tested AO31-A2.3 fracture model, we conclude that intramedullary implants should be preferred in these, unstable, fractures.
authors.affiliation: Department of Trauma-, Hand- and Reconstructive Surgery, University Medical Center Hamburg-Eppendorf, Martinistraße 52, 20246, Hamburg, Germany, l.weiser@uke.de.
authors.forename: Lukas
authors.initials: L
authors.lastname: Weiser
authors.forename: Andreas A
authors.initials: AA
authors.lastname: Ruppel
authors.forename: Jakob V
authors.initials: JV
authors.lastname: Nüchtern
authors.forename: Kay
authors.initials: K
authors.lastname: Sellenschloh
authors.forename: Johannes
authors.initials: J
authors.lastname: Zeichen
authors.forename: Klaus
authors.initials: K
authors.lastname: Püschel
authors.forename: Michael M
authors.initials: MM
authors.lastname: Morlock
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Lehmann
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005260:Female; D005264:Femoral Fractures / Q000000981:diagnostic imaging / Q000601:surgery*; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D011859:Radiography; D011897:Random Allocation; D016474:Weight-Bearing