Wear and surface cracking in early retrieved highly cross-linked polyethylene acetabular liners

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Tribology

Background:

• Cross-linking enhances ultra-high molecular weight polyethylene (UHMWPE) tribological properties in lab settings.
• In vivo wear behavior of highly cross-linked UHMWPE acetabular liners requires further investigation.

Purpose of the Study:

• To investigate in vivo wear mechanisms in retrieved highly cross-linked polyethylene acetabular liners.
• To determine if early in vivo wear behavior is accurately predicted by hip-simulator studies.

Main Methods:

• Examined 24 liners (21 explanted, 1 unimplanted highly cross-linked; 2 explanted non-cross-linked).
• Average patient age 59.9 years, average in vivo time 10.1 months.
• Assessed articular surface damage using optical scoring and evaluated micromechanisms via scanning electron microscopy.

Main Results:

• Explant damage scores averaged 11 (front) and 6.7 (back).
• Consistent early surface deformation and cracking observed in all explants.
• Observed surface changes included cracking, abrasion, pitting, and scratching, with altered machining marks.

Conclusions:

• Retrieved highly cross-linked UHMWPE liners showed surface damage not predicted by in vitro studies after ~10 months.
• Despite surface damage, no clinical failures due to wear were reported.
• Discrepancies may stem from in vivo lubrication/loading variations or limitations of long-term simulator studies in capturing early damage.