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An Anesthesia, Surgery, and Harvest Method for the Evaluation of Transpedicular Screws Using an In Vivo Porcine Lumbar Spine Model
Published on: May 31, 2017
Does placing screws off-centre in tubular bone alter their pullout strength?
1Royal Glamorgan Hospital, Llantrisant, United Kingdom. acharya.ashok@gmail.com
Injury
|June 16, 2009
Summary
Screws placed near the bone edge risk fracture and fixation failure. Optimal screw placement is within the central three-fourths of the bone for enhanced stability.
Area of Science:
- Orthopedic Surgery
- Biomechanical Engineering
- Materials Science
Background:
- Bone screws are critical for fracture fixation, often used directly or with plates.
- Concerns exist regarding screw placement at the bone's edge and its impact on fixation stability.
- Previous hypotheses suggest edge placement may compromise fixation and increase fracture risk.
Purpose of the Study:
- To investigate the effect of screw transverse plane position on pullout strength in porcine femora.
- To determine if edge placement of cortical screws influences fixation integrity.
- To provide evidence-based recommendations for optimal screw insertion in orthopedic procedures.
Main Methods:
- Cortical screws were inserted into porcine femora at various positions: center, off-center, and edge.
- Screw pullout strength was assessed using axial loading to failure.
- Fracture incidence and location relative to screw placement were analyzed.
- Statistical analysis was performed to correlate screw position with pullout strength and fracture occurrence.
Main Results:
- 'Edge' screws exhibited a higher incidence of fractures during pullout testing (4 out of 8).
- Fractured 'edge' screws demonstrated significantly lower pullout resistance compared to non-fractured 'edge' and all 'non-edge' screws.
- A statistically significant association was found between 'edge' screw placement and fracture likelihood (p=0.000).
Conclusions:
- Cortical screw placement within 12.5% of the bone edge significantly increases the risk of fixation failure due to fractures.
- Optimal screw insertion in the transverse plane should be within the central three-fourths of the bone.
- Avoiding edge placement enhances screw fixation stability and reduces the risk of iatrogenic fractures during axial loading.
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