Objectives: To compare the biomechanical properties of lag screw insertion in a laboratory model. Two blades, the Synthes Dynamic Helical Hip Screw (DHHS) and Proximal Femoral Nail Antirotation (PFNA), and two screws, the Synthes Dynamic Hip Screw (DHS) and Stryker Gamma 3 lag screw, were compared.

Setting: Orthopaedic biomechanics laboratory.

Design: Insertion testing was carried out in high and low density polyurethane foam mounted and attached to a Zwick Roell Amsler Hydrowin.

Outcome Measures: The axial load and torque during insertion of the implants was measured.

Results: The force required to insert the DHHS and PFNA blades was greater than the DHS and Gamma 3 screws into both low and high density foam. The force required to insert the DHHS and PFNA blades into high density foam was greater than low density foam. The torque required to insert the DHHS and PFNA blades into high density foam was less than that to insert the DHS and Gamma 3 screws. The torque required to insert the DHS and Gamma 3 screws into low density foam was less than the DHHS and PFNA blades. The torque during insertion of the DHHS and PFNA blades seemed to be independent of foam density.

Conclusions: The insertional properties of blades are significantly different to screws and this may have clinical importance.