Hand-Drilled External Fixator Pins Have Superior Biomechanical Strength Compared to Power-Drilling

In austere environments, surgeons commonly use a manual brace instead of a power drill to insert external fixation pins. Yet the biomechanical performance of manually inserted pins is uncertain. This study aimed to compare the pull-out strength of external fixator pins inserted with a manual brace with that of pins inserted with a power drill. We hypothesized that manual insertion would result in reduced pull-out strength compared to powered methods.

Self-drilling, self-tapping external fixator pins were inserted into 90 porcine femoral shaft segments using 3 techniques: hand drilled, power drilled, and pre-drilled/power-inserted. Each of the 3 techniques was performed by 3 surgeons, with a total of 30 specimens per technique and equal distribution between diaphyseal and metaphyseal bone. Pull-out strength to failure was measured using a materials testing machine. A generalized linear mixed effects model (GLMM) (least squares means [LMS] ± standard error) and post hoc pairwise comparisons were utilized for statistical analysis.

A GLMM identified drilling technique (P = .02) and diaphyseal pin location (P = .03) as significant predictors of pin pull-out strength, while the performing surgeon had no significant effect. Contrary to the hypothesis, post hoc pairwise analysis demonstrated hand drilled pins (LMS: 1,542.6 N ± 74.7) had significantly greater pull-out strength compared to both power drilled (LMS: 1,344.2 N ± 74.1) and pre-drilled/power-inserted pins (LMS: 1,248.5 N ± 89.8) (P = .05 and .006, respectively). No significant difference was observed between the power drilled and pre-drilled power-inserted techniques.

The pull-out strength of pins inserted with a hand brace was superior to that of pins inserted with power tools. This finding challenges common assumptions about the mechanical inferiority of manual drilling. These findings support the continued use and funding of hand drilled external fixator training programs within military and humanitarian aid settings. Finally, pre-drilling does not appear to confer any mechanical advantage over direct, powered pin insertion.