Crack-growth properties of various elastomers with potential application in small joint prostheses

Area of Science:

• Biomaterials science
• Orthopedic implant materials
• Polymer engineering

Background:

• Silastic small joint spacers for metacarpophalangeal joints have a high failure rate (2-26%).
• Failure is speculated to result from flaw propagation on the material surface, introduced during manufacturing, handling, or use.
• A need exists for improved elastomeric materials with enhanced durability.

Purpose of the Study:

• To compare the crack-growth properties of novel elastomeric materials with Silastic.
• To identify a self-hinging joint spacer material with increased functional life.
• To evaluate polyurethanes (ChronoFlex, Medicaflex) and a thermoplastic elastomer (Santoprene) against Silastic.

Main Methods:

• Materials were sterilized using ethylene oxide or gamma irradiation.
• Crack-growth properties were assessed using an ASTM standard flexing machine.
• Testing was conducted under high humidity and body temperature, both before and after artificial aging.

Main Results:

• ChronoFlex, Medicaflex, and Santoprene exhibited significantly lower crack-growth rates compared to Silastic (p < 0.001).
• All tested materials demonstrated improved crack resistance over Silastic under simulated physiological conditions.

Conclusions:

• Polyurethanes (ChronoFlex, Medicaflex) and Santoprene show promise as superior alternatives to Silastic for small joint spacers.
• These materials may offer enhanced longevity and reduced failure rates in metacarpophalangeal joint implants.
• Further clinical evaluation is warranted to confirm the long-term efficacy of these novel biomaterials.