title: Control of the micromovements of a composite-material nail design: A finite element analysis.
abstract: BACKGROUND
  Intramedullary nail fixation is the most accepted modality for stabilizing long bone midshaft fractures. The commercially used nails are fabricated from Stainless Steel or Titanium. Composite-materials (CM) mainly carbon-fiber reinforced polymers (CFRP) have been gaining more interest and popularity due to their properties, such as modulus of elasticity close to that of bone, increased fatigue strength, and radio-opacity to irradiation that permits a better visualization of the healing process. The use of CFRP instead of metals allows better control of different directional movements along a fracture site. The purpose of this analysis was to design a CM intramedullary nail to enable micromovements as depicted on a finite element analysis method.
  
  
  METHODS
  We designed a three-dimentional femoral nail model. Three CFRP with different laminates arrangements, were included in the analysis. The finite element analysis involved applying vertical and horizontal loads on each of the designed and tested nails.
  
  
  RESULTS
  The nails permitted a transverse micromovement of 0.75mm for the 45° lay-up and 1.5mm for the 90° lay-up for the CM, 1.38mm for the Titanium and 0.74mm for the Stainless Steel nails. The recorded axial movements were 0.53mm for the 45° lay-up, 0.87mm for the 90° lay-up, 0.46mm for the unsymmetrical lay-up CM, 0.046 for the Titanium and 0.02 for the Stainless Steel nails. Overall, the simulations showed that nail transverse micromovements can be reduced by using 45° carbon fiber orientations. Similar results were observed with each metal nails.
  
  
  CONCLUSIONS
  We found that nail micromovements can be controlled by changing the directional stiffness using different lay-up orientations. These results can be useful for predicting nail micromovements under specified loading conditions which are crucial for stimulating callus formation in the early stages of healing.
authors.affiliation: Orthopaedic Division, Sourasky, Tel-Aviv Medical Center, Tel-Aviv University, Israel.
authors.forename: Mor
authors.initials: M
authors.lastname: Ben-Or
authors.affiliation: Faculty of Mechanical Engineering, Tel-Aviv University, Israel.
authors.forename: Ronen
authors.initials: R
authors.lastname: Shavit
authors.affiliation: Orthopaedic Division, Sourasky, Tel-Aviv Medical Center, Tel-Aviv University, Israel.
authors.forename: Tomer
authors.initials: T
authors.lastname: Ben-Tov
authors.affiliation: Orthopaedic Division, Sourasky, Tel-Aviv Medical Center, Tel-Aviv University, Israel.
authors.forename: Moshe
authors.initials: M
authors.lastname: Salai
authors.affiliation: Orthopaedic Division, Sourasky, Tel-Aviv Medical Center, Tel-Aviv University, Israel. Electronic address: steinberge@tlvmc.gov.il.
authors.forename: Ely L
authors.initials: EL
authors.lastname: Steinberg
mesh_terms: D001858:Bone Nails; D002244:Carbon / Q000737:chemistry*; D005269:Femur / Q000293:injuries / Q000601:surgery; D020342:Finite Element Analysis; D009038:Motion; D011108:Polymers / Q000737:chemistry*; D011474:Prosthesis Design
chemical_list: D011108:Polymers; D002244:Carbon
keywords: Carbon fiber reinforced polymer; Femoral nail; Finite element analysis; Laminate lay-up orientation