Should Inter-Prosthetic Screws Be Placed When Prophylactically Plating a Femur?

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Materials science

Background:

• Apposing intramedullary femoral implants increase interprosthetic fracture risk.
• Optimal screw configuration for prophylactic plating is undetermined.

Purpose of the Study:

• Determine the optimal screw configuration for prophylactic plating of femurs with interprosthetic segments.
• Evaluate the biomechanical impact of screw placement in the interprosthetic distance (IPD).

Main Methods:

• 2- and 10-cm IPD created in 21 composite femora with intramedullary implants.
• 4.5 mm plates applied with either one screw (IP-1) or zero screws (IP-0) in the IPD.
• Femora loaded to failure in four-point bending; force-at-failure (FAF) and energy-to-failure (ETF) compared.
• Digital image correlation (DIC) analyzed surface strain distributions.

Main Results:

• IP-0 configurations (no screws in IPD) showed significantly higher FAF and ETF than IP-1.
• FAF and ETF for 10-cm IPD without screws were comparable to native femora.
• Strain analysis revealed concentrated stress at screw tips exiting the medial cortex.

Conclusions:

• A bicortical screw in the IPD acts as a stress riser, reducing FAF and ETF.
• Femora with IPD ≥ 10 cm exhibit biomechanical properties similar to native bone.
• Bridging constructs are recommended for prophylactic plating of femora with IPD < 10 cm to mitigate fracture risk.