Pullout Strength of Pedicle Screws Inserted Using Three Different Techniques: A Biomechanical Study on Polyurethane...

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Materials Science

Background:

• Pedicle screw fixation is crucial for spinal stability.
• Pullout strength is a key performance indicator influenced by screw design, insertion technique, and bone quality.

Purpose of the Study:

• To evaluate the pullout strength of three distinct pedicle screw designs.
• To compare the impact of three insertion strategies on screw fixation.
• To assess the effect of cyclic pre-loading on pedicle screw pullout strength.

Main Methods:

• Three pedicle screw types (single-lead-thread (SLT), dual-lead-thread (DLT), mixed-single-lead-thread (MSLT)) were tested.
• Screws were inserted into polyurethane foam blocks using three strategies: full insertion (A), insertion with reversal (B), and partial insertion (C).
• Pullout strength was measured with and without cyclic pre-loading, analyzed using Kruskal-Wallis and Mann-Whitney-U tests.

Main Results:

• Strategy A (full insertion) yielded significantly higher pullout strength than strategies B and C under all conditions.
• Without pre-loading, MSLT screws showed greater pullout strength than SLT and DLT screws across all strategies.
• Pre-loading reduced fixation strength for all screws; MSLT screws with strategy B exhibited the lowest pullout strength (p < 0.05).

Conclusions:

• The MSLT pedicle screw generally offers the highest pullout strength, except when using strategy B with cyclic pre-load.
• Insertion strategy B (screw-out adjustment) compromises fixation strength for all screw types, with MSLT showing the largest reduction.
• Recommendations suggest avoiding screw-out adjustments during initial insertion to maintain optimal pedicle screw fixation.