Changes in the bone-cement interface after total hip replacement. An in vivo animal study

Area of Science:

• Orthopedic Surgery
• Biomaterials Science
• Biomechanical Engineering

Background:

• Loosening of cemented femoral components is a common complication in total hip replacement (THR).
• Clinical specimens for studying early loosening are scarce due to the need for complete failure before revision surgery.
• A reliable animal model is needed to investigate the temporal sequence of changes at the bone-cement interface.

Purpose of the Study:

• To develop and utilize a sheep model to study the sequential changes around the femoral component after total hip replacement.
• To investigate the causes of bone-cement interface failure and decreased torsional rigidity.

Main Methods:

• Implantation of plastic-on-metal THR prostheses in sheep.
• Ambulation on a concrete surface initiated six weeks postoperatively.
• Assessment of radiographic, histological, mechanical, bacteriological, and chemical changes.

Main Results:

• All sheep exhibited decreased torsional rigidity between the prosthesis and femoral cortex.
• Bone-cement interface failure was observed.
• Alterations in functional stress due to prosthesis insertion were identified as the most probable cause of failure, rather than polymerization, toxicity, or infection.

Conclusions:

• The developed sheep model effectively demonstrated decreased torsional rigidity and bone-cement interface failure.
• Mechanical or vascular effects associated with prosthesis insertion appear to be the primary drivers of interface degradation.
• Degenerative changes at the bone-cement interface may be an inherent and unavoidable aspect of cemented THR.