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Cortex distraction forces caused by the insertion of external fixator pins
C I Moorcroft1, P B Thomas, S Verborg
1Bionics Laboratory Hartshill Orthopaedic & Surgical Unit, City General Hospital, Stoke-on-Trent, UK.
Journal of Orthopaedic Trauma
|October 17, 2001
Summary
Inserting bicortical pins into long bones generates significant distraction forces between bone cortices. This can potentially worsen fractures, necessitating careful pin placement away from defects.
Area of Science:
- Orthopedic biomechanics
- Surgical implant research
- Bone fracture mechanics
Background:
- External fixator pins are crucial for bone fracture stabilization.
- Bicortical pin insertion can inadvertently damage bone, leading to complications like crack propagation.
- Understanding forces during pin insertion is vital for preventing adverse effects.
Purpose of the Study:
- To quantify the distraction forces generated between bone cortices during bicortical pin insertion.
- To assess if drilling and inserting bicortical pins can cause significant inter-cortical forces.
Main Methods:
- Utilized a specialized force measurement column with parallel bone or bone substitute samples.
- Inserted three common bicortical pin designs: tapered, self-threading and self-drilling, and self-threading.
- Measured axial thrust and inter-cortical distraction forces during pin insertion.
Main Results:
- All tested pin designs generated substantial distraction forces, typically ranging from 700 to 1,000 Newtons.
- Significant forces were consistently measured between the bone cortices across different pin types.
Conclusions:
- Bicortical pin insertion, using common designs, can create large inter-cortical distraction forces.
- These forces may exacerbate existing fractures or propagate undisplaced fractures.
- Careful selection of pin insertion sites, avoiding local bone defects, is clinically significant.