Acrylic fragmentation in total hip replacements and its biological consequences

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Immunology

Background:

• Total joint prostheses loosening is often linked to acrylic cement fragmentation.
• Particulate acrylic debris triggers adverse biologic responses at the bone-cement interface.

Purpose of the Study:

• To investigate the fractographic features of retrieved femoral cement mantles.
• To characterize the biologic response to particulate acrylic debris.
• To determine the role of the immune system in this reaction.

Main Methods:

• Fractographic analysis of explanted cement mantles.
• Histologic and immunohistochemical examination of human and animal tissues.
• Organ culture studies of bone resorption.
• In vivo studies using immunocompetent and immunodeficient mice.

Main Results:

• Cement fractures and wear were common, releasing particulate acrylic debris.
• A macrophage and giant-cell foreign-body granulomatous reaction occurred in response to particulate, not bulk, cement.
• This reaction, capable of bone resorption, was induced by particulate polymethylmethacrylate (PMMA) in all tested mouse strains, regardless of immune status.
• The reaction was sustained by nonimmune phagocytosis and macrophage activation, not classic immune mechanisms.

Conclusions:

• Acrylic cement fragmentation is a key factor in joint prosthesis loosening.
• The biologic response to particulate cement is a nonimmune, macrophage-mediated foreign-body reaction.
• This reaction contributes to bone resorption and implant failure independently of the host's immune system.