Biomechanics of cemented and cementless prostheses

Area of Science:

• Orthopedic Surgery
• Biomaterials Science
• Biomechanics

Background:

• Cemented arthroplasty relies on cement for stability, bone contact, and isoelastic properties.
• Cementless components aim for bone ingrowth but face challenges in achieving initial stability and precise fit.
• Understanding the mechanical behavior of both cemented and cementless femoral components is critical for improving total hip arthroplasty outcomes.

Purpose of the Study:

• To compare the initial stability of cemented versus uncemented femoral components in simulated physiological conditions.
• To evaluate the potential impact of micromotion on bone ingrowth for cementless components.
• To analyze failure modes of cemented femoral components in retrieved human specimens.

Main Methods:

• In vitro experimental study measuring micromotion of cemented and uncemented femoral components under simulated single limb stance and stair climbing.
• Autopsy studies of retrieved femurs from patients with well-functioning cemented total hip arthroplasty.

Main Results:

• Both cemented and uncemented components demonstrated high stability during simulated single limb stance (<50 microns motion).
• Uncemented components exhibited significantly greater instability during simulated stair climbing (280 microns) compared to cemented components (76 microns).
• Failure analysis of cemented components revealed mechanical factors like cement-prosthesis debonding and fractures, not lack of bone ingrowth.

Conclusions:

• Cemented femoral components provide superior initial stability, especially under dynamic loading, which may be advantageous for bone ingrowth.
• Challenges with cemented components include interface strength and cement integrity.
• Difficulties with cementless components involve precise femoral canal preparation and achieving rigid fixation.