title: A novel intramedullary nail for micromotion stimulation of tibial fractures.
abstract: BACKGROUND
  Animal studies and clinical trials have suggested that early application of controlled axial micromotion can accelerate healing of long bone fractures compared to rigid fixation. However, experimental investigations of micromotion constructs have been limited to external fixators, which have a higher incidence of complications than intramedullary nails. The purpose of this study was to assess whether a novel intramedullary nail design can generate stimulatory micromotion under minimal weight-bearing loads typical of the early healing period.
  
  
  METHODS
  Eight cadaver tibiae were reamed, osteotomised, and implanted with commercially-available IM nails fitted with a custom insert that allowed 1mm of axial micromotion after proximal/distal interlocking. Specimens were mounted in a materials testing machine and subjected to cyclic axial loading while interfragmentary motion was measured using an extensometer. Implants were also tested in standard statically-locked mode.
  
  
  RESULTS
  The average force required to cause distraction of the fracture gap in micromotion mode was 37.0 (SD 21.7) N. The mean construct stiffness was 1046.8 (SD 193.6) N/mm in static locking mode and 512.4 (SD 99.6) N/mm in micromotion mode (significantly different, P<0.001).
  
  
  CONCLUSIONS
  These results support the development of a micromotion-enabled IM nail because the forces required to cause interfragmentary movements are very low, less than the weight of the hanging shank and foot. In contrast to rigid-fixation nails, which require significant weight-bearing to induce interfragmentary motion, the micromotion-enabled nail may allow movement in non-weight-bearing patients during the early healing period when the benefits of mechanical stimulation are most critical.
authors.affiliation: Medical Engineering Design and Innovation Centre, Department of Biomedical Engineering, Cork Institute of Technology, Bishopstown, Cork, Ireland. HLDailey@gmail.com
authors.forename: Hannah L
authors.initials: HL
authors.lastname: Dailey
authors.forename: Charles J
authors.initials: CJ
authors.lastname: Daly
authors.forename: John G
authors.initials: JG
authors.lastname: Galbraith
authors.forename: Michael
authors.initials: M
authors.lastname: Cronin
authors.forename: James A
authors.initials: JA
authors.lastname: Harty
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D019544:Equipment Failure Analysis; D005260:Female; D005594:Fracture Fixation, Intramedullary / Q000295:instrumentation* / Q000379:methods*; D006801:Humans; D008297:Male; D009038:Motion; D011474:Prosthesis Design; D013978:Tibial Fractures / Q000503:physiopathology* / Q000601:surgery*; D016896:Treatment Outcome