title: Finite element comparison of retrograde intramedullary nailing and locking plate fixation with/without an intramedullary allograft for distal femur fracture following total knee arthroplasty.
abstract: OBJECTIVE
  Periprosthetic distal femur fracture after total knee arthroplasty due to the stress-shielding phenomenon is a challenging problem. Retrograde intramedullary nail (RIMN) or locking plate (LP) fixation with/without a strut allograft has been clinically used via less invasive stabilization surgery (LISS) for the treatment of these periprosthetic fractures. However, their biomechanical differences in construct stability and implant stress have not been extensively studied, especially for the osteoporotic femur.
  
  
  METHODS
  This study used a finite-element method to evaluate the differences between RIMN, LP, and LP/allograft fixation in treating periprosthetic distal femur fractures. There were sixteen variations of two fracture angles (transverse and oblique), two loading conditions (compression and rotation), and four bony conditions (one normal and three osteoporotic). Construct stiffness, fracture micromotion, and implant stress were chosen as the comparison indices.
  
  
  RESULTS
  The LP/allograft construct provides both lateral and middle supports to the displaced femur. Comparatively, the LP and RIMN constructs, respectively, transmit the loads through the lateral and middle paths, thus providing more unstable support to the construct and high stressing on the implants. The fracture pattern plays a minor role in the construct stabilization of the three implants. In general, the biomechanical performances of the RIMN and LP constructs were comparable and significantly inferior to those of the LP/allograft construct. The bone quality should be evaluated prior to the selection of internal fixators.
  
  
  CONCLUSIONS
  The LP/allograft construct significantly stabilizes the fracture gap, reduces the implant stress, and serves as the recommended fixation for periprosthetic distal femur fracture.
authors.affiliation: Department of Orthopedics, Tzu-Chi General Hospital at Taichung, and Tzu Chi University, Taiwan.
authors.forename: Shih-Hao
authors.initials: SH
authors.lastname: Chen
authors.affiliation: Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan.
authors.forename: Ming-Chieh
authors.initials: MC
authors.lastname: Chiang
authors.affiliation: Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan. Electronic address: chhung@mail.nctu.edu.tw.
authors.forename: Ching-Hua
authors.initials: CH
authors.lastname: Hung
authors.affiliation: Graduate Institute of Biomedical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
authors.forename: Shang-Chih
authors.initials: SC
authors.lastname: Lin
authors.affiliation: Department of Mechanical Engineering, National Chiao Tung University, Hsinchu, Taiwan.
authors.forename: Hsiao-Wei
authors.initials: HW
authors.lastname: Chang
mesh_terms: D064591:Allografts; D019645:Arthroplasty, Replacement, Knee; D001860:Bone Plates; D016025:Bone Transplantation; D005264:Femoral Fractures / Q000503:physiopathology / Q000601:surgery*; D020342:Finite Element Analysis; D005594:Fracture Fixation, Intramedullary; D006801:Humans; D008297:Male; D008422:Materials Testing; D008875:Middle Aged; D008954:Models, Biological; D020370:Osteoarthritis, Knee / Q000503:physiopathology / Q000601:surgery; D057068:Periprosthetic Fractures / Q000503:physiopathology / Q000601:surgery*; D012399:Rotation; D013314:Stress, Mechanical
keywords: Distal femur fracture; Intramedullary; Intramedullary allograft; Knee arthroplasty; Osteoporotic femur; Retrograde nail