Fully-Tapped? Undertapped? Untapped? Does Pilot Hole Preparation Affect the Pullout Strength of Pedicle Screws Placed in Different Regions of the Thoracic and Lumbar Spine?

136 pedicle screws were placed in 4 human cadaveric spines from T1 to S1. A total of 53 pedicles were fully-tapped, 53 were untapped, and 35 were 1mm-undertapped. Instron testing for direct axial pullout was performed.

RESULTS: ANOVA testing revealed no significant differences in pullout strength (p=.688). Paired T-test direct comparison also did not demonstrate significant differences (p >.05). Higher specimen lumbar BMD correlated with increasing pullout strength (Pearson Corr Coeff = .82). No correlation was noted between insertional torque and pullout strength ( Pearson Corr Coeff = .631).

CONCLUSIONS: There are no significant differences in the pullout strength of pedicle screws inserted using either fully, partially, or untapped pilot holes in any region of the human thoracic and lumbar spine. Pullout strength is lowest in the upper thoracic spine regardless of pilot hole preparation technique. Higher lumbar spine BMD is associated with greater screw pullout strength.