title: [Stress test and clinical application of the minimal-invasive dynamic hip screw].
abstract: OBJECTIVE
  To recognize the effect of minimal-invasive dynamic hip screw (MIDHS) on the treatment of intertrochanteric fracture of the hip by biomechanical test and preliminary clinical application.
  
  
  METHODS
  Ten artifical made intertrochanteric fractures of femoral specimen from five cadavers were divided into two groups randomly. The fractures in first group were fixed by MIDHS and other group were fixed by dynamic hip (DHS). Biomechanical characteristics of two different devices were compared with the biomechanical character of load-straining, load-displacing, rigidity and strength of femur by statistic analysis. According to the Harris evaluation, healing effect of intertrochanteric fractures was evaluated clinically on the 15 cases.
  
  
  RESULTS
  Straining changes of MIDHS were 14% and 11% less than that of DHS on the tensile side and the pressure side respectively; Sinking and horizontal displacement, were 19% and 22% less than that of DHS respectivly. But external and internal stress intensity,axial and bending rigidity were all higher than that of DHS, they were 12%, 11%, 19% and 37%. Maximal destroyed twisting moment (15%) and average twisting rigidity (15%) were both higher than that of DHS, but twisting angle was 18% less. Under the force, of 1 800 N, the open angle of the fracture on transverse section was 2.28 degrees,while the DHS's was 3.60 degrees . The data above were significant differences statistically (P < 0.01). The average Harris score of the 15 cases with intertrochanteric fractures treated by MIDHS was 91, excellent and good rate was 92.7%, without complications of internal fixation failure,postoperative infection and so on.
  
  
  CONCLUSIONS
  The design of minimal-invasive dynamic hip screw is reasonable and effective against rotating, shearing and varus stress force of the fracture, and it provides possibility of implanting the internal fixation with minimal incision. So it is an ideal internal fixation device for the treatment of intertrochanteric fractures.
authors.affiliation: Department of Orthopaedics, Cixi Peoples Hospital, Cixi 315300, Zhejiang, China.
authors.forename: Song-Lin
authors.initials: SL
authors.lastname: Tong
authors.forename: Jian-Lie
authors.initials: JL
authors.lastname: Chen
authors.forename: Wen-Jie
authors.initials: WJ
authors.lastname: Lu
authors.forename: Zhi-Jun
authors.initials: ZJ
authors.lastname: Pan
authors.forename: Yi-Jin
authors.initials: YJ
authors.lastname: Wang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001863:Bone Screws; D005260:Female; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods; D006620:Hip Fractures / Q000601:surgery*; D006801:Humans; D016268:Internal Fixators; D008297:Male; D008875:Middle Aged