Implicit modeling of screw threads for efficient finite element analysis of complex bone-implant systems

Area of Science:

• Orthopedic biomechanics
• Computational modeling
• Finite element analysis

Background:

• Finite element analysis (FEA) is crucial for orthopedic device development.
• Simplifying FEA models improves simulation efficiency without sacrificing accuracy for relative comparisons.
• Screw cut-out in osteoporotic bone is a significant clinical concern.

Purpose of the Study:

• To develop and evaluate a pseudo-threaded model approximating screw behavior using a smooth cylinder and contact conditions.
• To compare the accuracy and efficiency of the pseudo-threaded model against explicitly modeled threads and a bonded interface.
• To assess the impact of interface modeling on implant stability comparisons in proximal humerus fractures.

Main Methods:

• Developed a pseudo-threaded model representing screws implicitly via interfacial contact.
• Calibrated the pseudo-threaded model against FEA simulations with explicit thread geometry and frictional contact.
• Performed parametric analysis on screw-in-bone systems with varying loads and bone moduli.
• Compared pseudo-threaded and bonded interfaces in a 3-part proximal humerus fracture model across 10 patients.

Main Results:

• The pseudo-threaded model predicted screw displacement with 1-5% difference compared to explicit models.
• The pseudo-threaded model provided more accurate strain estimations than a bonded interface.
• Interface modeling choice did not affect relative implant stability comparisons in proximal humerus fractures.

Conclusions:

• The pseudo-threaded model is an efficient and accurate method for simulating screw mechanics in orthopedic applications.
• A bonded interface can be an efficient surrogate for relative comparisons between implants with identical thread profiles.
• These findings can streamline the evaluation of orthopedic implants, particularly in complex fracture scenarios.