title: Intertrochanteric fracture: Association between the coronal position of the lag screw and stress distribution.
abstract: OBJECTIVE
  The best position of the lag screw in the femoral head for the fixation of intertrochanteric fracture is controversial. Traditional view suggests that it should be positioned in the central axis of the femoral neck with a tip-apex distance (TAD) of <25 mm, but the mechanical properties have not been reported yet. Herein, we aimed to investigate internal fixation with the lag screw placed in different positions on the femoral coronal plane by performing a finite element analysis and to identify a reasonable lag screw position after the internal stress distributions at the femoral head.
  
  
  METHODS
  A three-dimensional finite element model of a healthy male's femur was set up, on which the intertrochanteric fracture model with proximal femoral nail antirotation (PFN-A) was based. Nine modalities of the model were established in accordance with different lag screw positions in the femoral head. Three-dimensional finite element calculations were conducted, and the distribution trends of characteristic high-stress concentration points were observed.
  
  
  RESULTS
  The area of high-stress concentration was distributed from the top of the femoral head to the medial cortex of the trochanteric region. Four characteristic high-stress concentration points were observed, and the following trends indicated that the lower the position of the lag screw, the greater its length.
  
  
  CONCLUSIONS
  A longer and lower lag screw may make the fixation sustain greater stress, reduce bone tissue stress correspondingly in intertrochanteric fractures fixated with PFN-A, and sustain greater stress and more cyclic load at the same bone density.
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital of Southern Medical University, Guangzhou 510515, China; Department of Orthopaedics, Guangdong General Hospital and Guangdong Academy of Medical Sciences, Guangzhou 510080, China.
authors.forename: Changxiang
authors.initials: C
authors.lastname: Liang
authors.affiliation: Department of Ophtalmology, Third Affiliated Hospital of Sun Yat-sen University, Guangzhou 510630, China.
authors.forename: Ruiping
authors.initials: R
authors.lastname: Peng
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital of Southern Medical University, Guangzhou 510515, China.
authors.forename: Nan
authors.initials: N
authors.lastname: Jiang
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital of Southern Medical University, Guangzhou 510515, China.
authors.forename: Guoping
authors.initials: G
authors.lastname: Xie
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital of Southern Medical University, Guangzhou 510515, China.
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Orthopaedics and Traumatology, Nanfang Hospital of Southern Medical University, Guangzhou 510515, China. Electronic address: binyudoc@163.com.
authors.forename: Bin
authors.initials: B
authors.lastname: Yu
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001863:Bone Screws; D005270:Femur Head / Q000601:surgery*; D020342:Finite Element Analysis; D005593:Fracture Fixation, Internal / Q000295:instrumentation* / Q000379:methods*; D006620:Hip Fractures / Q000601:surgery*; D006801:Humans; D008297:Male; D008953:Models, Anatomic; D013314:Stress, Mechanical
keywords: PFN-A; cut-out; finite element analysis; intertrochanteric fracture; lag screw position