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Central placement of screw fixation in scaphoid fracture—a computational approach and biomechanical study. Yang Guo MD, FHKCOS Associate Consultant Department of Hand Surgery, Ji Shui Tan hospital, beijing , China. - PowerPoint PPT Presentation
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Central placement of screw fixation in scaphoid fracture—a computational approach and biomechanical study
Yang Guo MD, FHKCOSAssociate ConsultantDepartment of Hand Surgery, Ji Shui Tan hospital, beijing, China
OPTIMAL position of fixation for scaphoid fractures continues to be debatedCentral placement : supported
by(Tremble,Mccallister,2000)biomechanical studies /clinical evaluations Has been accepted as a prefered method of fixationRecently, some studies :(Luria 2010,2012) biomechanical studies /finite element analysissuggested no difference in stability between central and eccentric placement
The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits.
To be central or Not to be?Our study consisted of 2 parts
Establishment “central” concept computational approach
Biomechanical test central Vs peripheral
1 Establishing “Central”
Shrinkage in a uniform manner in software-- pre-op planning systemScaphoid surface model was extracted.One pixel space was allowed by one time of shrinkage in the programScaphoid model: smaller and smaller
Scahpoid distal pole
Scahpoid proximal pole
Waist portion
Central one third
Further shrinkage of 1.5mm
Central zone
Central one-third zone and central zone
Central zone-geometry
Screw axis
Part 2: Biomechanical Study Design : Types of fixation
Fracture Plane Location of Screw
Group 1 Proximal Proximal Central Zone
Group 2 Proximal Distal Central Zone(eccentric)
Group 3 Distal Distal Central Zone
Group 4 Distal Proximal Central Zone(eccentric)
Biomechanical study : osteotomy design
Group 1 Group 2
Group 3Group 4
Screw axisthread
Fracture plane
Materials and Test machine
Estimation of sample size and power10 of scaphoids , consistent with a previous dataData analysis: Wilcoxon nonparametric analysis Failure load of the specimens (P <0.05).The mode of failure :Screw migration fracture at the screw–bone interface, sliding along the fracture. None of the specimens dislodged from the potting fixtureNone of screw was bent
Stroke-Force curve
ResultsLoad to failure (N)
Dispalcement of fracture ( mm) Significance
Group 1 80.82±15.63 2.3±0.5 0.001
Group 2 58.32±17.18 3.1±0.5
Group 3 76.83±14.54 2.2±0.7 0.166
Group 4 73.38±13.32 2.5±0.6
Brief Disccussion
1. Concept of Central need to be clarified Straight central axis does not exist
2. Central placement : important as long as possible
LimitationsSame with any cadaveric biomechanical studyThe screw itself may contributed resistance ,when it was placed in a more horizontal direction
Saw bone material: Failure load lower than previous tests
We simplified the forces into a single vector and did not perform cyclic loading
Fx plane differed slightly, which affects its stability.
Thanks!