Behavior of a Modeled Hip Implant Insertion Device Through Finite Element Analysis

Open Access
Author:
Casey, Patrick Connor
Area of Honors:
Mechanical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Reuben H Kraft, Thesis Supervisor
  • Jacqueline Antonia O'Connor, Honors Advisor
Keywords:
  • Hip
  • Arthroplasty
  • Insertion Device
  • FEA
  • Impactor
  • Spring
  • Biomechanical Response
  • Impact
  • Stiffness
  • Geometry
  • Offset
Abstract:
During hip arthroplasty, an implanted acetabulum requires repeated impacts with a force of thousands of Newtons for a proper press fit into the hip. For the procedure, the surgeon has the option of using a geometrically straight or offset inserter depending on the situation at hand. The c-shaped, or offset, inserter generally has the advantage of being minimally invasive. However, it is important to understand the differences between each device to allow for proper application. There has been a concern over how to impact the c-shaped hip inserter, describing an unfamiliar sensitivity or feeling when applying a force. This issue could disrupt surgical processes and generate a higher risk of hip fracture. Therefore, this analysis explores the mechanical properties of each hip insertion device focusing on geometric differences to assist in visualizing how the inserters `feel' upon impact. Each hip inserter was simplified to mimic a straight or curved beam under axial loading. A static Free Body Diagram (FBD) analysis was used to attain mechanical properties such as reaction force, stress, and axial displacement for each inserter with a given impact load applied. Additionally, Castigliano's theorem was used to show that a curved nature induces more bending. An energy method was then used to show how forces, displacements, and stiffnesses relate to each other when the beams are modeled as springs. With a given kinetic energy, the relationship between a lower stiffness, increased strain energy, and therefore lower force applied was used to describe the biomechanical response (feeling) and force of the impact. An FEA model in Abaqus was created to demonstrate the physical phenomenon and visually compare the mechanics of the two inserters, this time using the results of the simulation for the c-shaped inserter. The c-shaped inserter proved to have a smaller spring stiffness coefficient `k' with an applied load or kinetic energy. Abaqus showed an increase in strain energy and deformation with the c-shape inserter, when given the same force as the straight one, indicating a lower stiffness. The lower stiffness therefore constitutes a lower reaction force when given the same impact kinetic energy.