Relative movements between Kinemax Plus tibial inserts and the tibial base-plates

Area of Science:

• Biomedical Engineering
• Orthopedic Surgery
• Materials Science

Background:

• Total knee replacements (TKRs) utilize tibial inserts and base plates, crucial for joint function.
• The interface between these components can influence implant longevity and performance.
• Understanding micromotion at this interface is vital for improving TKR design.

Purpose of the Study:

• To quantify the movement between tibial inserts and base plates in Kinemax Plus knee bearings.
• To assess how simulated walking loads affect this interface movement.
• To investigate the role of ultra-high molecular weight polyethylene (UHMWPE) creep.

Main Methods:

• Six large Kinemax Plus knee bearings with snap-fit designs were tested.
• A six-station knee wear simulator subjected bearings to 1 million cycles.
• Movement was measured using dial gauges under loaded and unloaded conditions.

Main Results:

• Initial movement occurred between the insert and base plate due to the snap-fit mechanism.
• This movement significantly decreased when the bearings were dynamically loaded.
• Unloaded movement after testing was reduced by 35% (AP) and 54% (ML), attributed to UHMWPE creep.

Conclusions:

• While in-vivo loading likely reduces micromotion, a potential second interface for wear may still exist.
• UHMWPE creep plays a role in the observed changes in insert-baseplate movement.
• Further investigation into interface mechanics is needed to optimize TKR designs and minimize wear.