Stress risers between two ipsilateral intramedullary stems: a finite-element and biomechanical analysis

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Biomaterials science

Background:

• Periprosthetic fractures are a significant complication following total joint replacement surgery.
• These fractures predominantly occur at the tip of the prosthetic stem.
• Understanding the biomechanical factors influencing stress distribution is crucial for preventing such fractures.

Purpose of the Study:

• To investigate the biomechanical effects of gap size, stem stability, and cortical thickness on femoral tensile stresses.
• To determine the influence of these factors on stress risers around intramedullary stems.

Main Methods:

• Utilized finite-element models to simulate stress distribution in the femur.
• Employed strain-gauge tests on a composite Sawbone femur for experimental validation.
• Analyzed the interplay between gap size, stem fixation (loose vs. well-fixed), and cortical bone thickness.

Main Results:

• Femoral stress levels were not significantly affected by the gap size between the stem and the bone.
• Decreased cortical thickness led to increased peak tensile stresses in the femur.
• Loose stem tips acted as significant stress risers, especially in femurs with thinner cortices.
• Well-fixed stem tips did not act as stress risers, regardless of gap size.

Conclusions:

• Cortical thickness is a critical factor in stress distribution around intramedullary stems.
• Stem stability is paramount in preventing stress concentration at the stem tip.
• Minimizing stress risers through optimal stem fixation may reduce the incidence of periprosthetic fractures in patients with varying bone quality.