Isoelastic distal ulnar head prosthesis: an in vitro joint simulator study

Area of Science:

• Biomaterials Science
• Orthopedic Surgery
• Tribology

Background:

• Distal radioulnar joint (DRUJ) instability often requires prosthetic arthroplasty.
• Matching the mechanical properties of the sigmoid notch is crucial for superior clinical outcomes.
• Cobalt chrome (CoCr) is a common material, but its tribological properties require further investigation.

Purpose of the Study:

• To investigate the feasibility of ultrahigh-molecular-weight polyethylene (UHMWPE) as a bearing material for ulnar head prostheses.
• To compare the tribology, specifically wear properties, of UHMWPE against cobalt chrome (CoCr) distal ulnar replacements.

Main Methods:

• In vitro joint simulation comparing UHMWPE and polished CoCr ulnar heads in physiologic saline.
• Wear simulation against a synthetic bone counterface for 1 million cycles.
• Fatigue testing of UHMWPE prostheses for 3.1 million cycles, followed by thermal analysis.

Main Results:

• UHMWPE exhibited a dynamic coefficient of friction (0.087 +/- 0.016) comparable to polished CoCr.
• Synthetic bone counterface wear was 45 times lower with UHMWPE compared to CoCr.
• Fatigued UHMWPE showed unchanged thermal properties and viscoelastic moduli.

Conclusions:

• UHMWPE demonstrates favorable low-friction and stable fatigue characteristics for ulnar head prostheses.
• Its low modulus of elasticity contributes to significantly reduced synthetic bone counterface wear versus CoCr.
• In vitro simulation suggests UHMWPE ulnar head prostheses have potential in DRUJ arthroplasty.