How a pilot hole size affects osteosynthesis at the screw-bone interface under immediate loading

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Materials Science

Background:

• Pilot hole size (PHS) significantly impacts screw-bone fixation.
• Understanding the biomechanical effects of PHS on fractured bone is essential for optimal osteosynthesis.

Purpose of the Study:

• To investigate the effect of varying pilot hole sizes (PHS) on the biomechanical environment of the screw-bone interface in fractured bone.
• To analyze screw insertion and immediate body weight pressure (BWP) effects on fixation stiffness.

Main Methods:

• Finite element models were used to simulate screw insertion and BWP.
• Four PHS (71% to 85% of screw external diameter, SED) were analyzed.
• Non-linear bone material behavior with ductile damage properties was incorporated.
• Numerical models were validated with experimental pull-out tests on synthetic bone.

Main Results:

• Smaller PHS (71% and 75.5% of SED) increased insertion torque within recommended levels.
• Smaller PHS maximized bone thread-screw contact area and bone radial deformation.
• Under BWP, stress exceeded the elastic limit, initiating ductile bone damage.
• Increasing PHS from 71% to 75.5% of SED increased bone microdisplacement (75 to 100 μm), reducing fixation stiffness.

Conclusions:

• Optimal PHS is critical for achieving stable screw-bone fixation.
• Smaller pilot holes enhance initial fixation stability and contact.
• Larger pilot holes compromise fixation stiffness and increase microdisplacement under load, potentially leading to implant failure.