Numerical Investigation Into Bone Remodeling Around Different Co-Polymeric Swelling Bone Anchors

Area of Science:

• Biomaterials Science
• Biomechanics
• Computational Biology

Background:

• Co-polymeric bone anchors are used in orthopedic applications.
• Understanding their hygro-mechanical response and bone interaction is critical for clinical success.
• Bone remodeling is influenced by mechanical stimuli, as described by Wolff's Law.

Purpose of the Study:

• To develop and validate a computational framework for simulating the hygro-mechanical response of co-polymeric bone anchors.
• To investigate the impact of bone anchor swelling on surrounding bone remodeling.
• To determine the optimal swelling ratio for bone densification and successful osteointegration.

Main Methods:

• Developed a hygro-elastic finite element framework coupled with a strain-energy-density based bone remodeling model.
• Conducted free swelling experiments with co-polymeric porous bone anchors (poly [methyl methacrylate-co-acrylic acid]) at 80/20 and 90/10 ratios in bovine serum.
• Simulated anchor swelling within bone models of varying densities and analyzed induced radial stresses.

Main Results:

• The 90/10 composition induced radial stresses leading to favorable bone densification (17.5%-54%).
• The 80/20 composition caused excessive swelling, inducing radial stresses exceeding 31 MPa, resulting in overload resorption, particularly in high-density bone.
• In vivo sheep studies confirmed the computational findings regarding bone remodeling responses.

Conclusions:

• The swelling ratio of co-polymeric bone anchors significantly influences bone remodeling.
• Controlled swelling (e.g., 90/10 ratio) promotes beneficial bone densification.
• Excessive swelling (e.g., 80/20 ratio) leads to detrimental overload resorption, compromising osteointegration.