In vitro wear of ultrahigh-molecular-weight polyethylene and vitamin E blended highly cross-linked polyethylene in linked, semiconstrained total elbow replacement prostheses.

BACKGROUND

The objectives of this study were to develop a clinically relevant in vitro elbow wear test and to compare the polyethylene wear of 2 total elbow replacement prostheses, one that uses conventional gamma-irradiated polyethylene (CPE) and one that uses vitamin E blended and cross-linked polyethylene (VE-HXPE) bushings.

MATERIALS AND METHODS

The test protocol applied 0° to 85° flexion-extension motions and imposed a constant 4.5° varus malalignment of the ulnar relative to the humeral implant under a variable joint load profile at a frequency of 1 Hz. The implants were tested for 3 million cycles (Mc) in a bovine serum lubricant at 37°C ± 3°C. Polyethylene wear was determined gravimetrically. Wear particles were isolated and characterized.

RESULTS

Clinically relevant polyethylene bushings wear mechanisms were observed. After 3 Mc, the mean CPE wear rate was 9.3 ± 2.8 mm/Mc, significantly lower than that reported for hip and knee implants but comparable to that of ankle (7.4 ± 1.3 mm/Mc) devices. The mean VE-HXPE wear rate was 0.8 ± 0.2 mm/Mc, comparable to that of hip and knees devices. The mean equivalent circle diameter and aspect ratio were 0.17 ± 0.01 µm and 1.99 ± 0.18 for the CPE and 0.15 ± 0.02 µm and 1.81 ± 0.16 for the VE-HXPE particles.

CONCLUSION

The test replicated clinically observed failure modes for CPE devices. The use of VE-HXPE led to an order of magnitude reduction in polyethylene wear. Further clinical evaluation is necessary to determine if this translates into reduced complications of total elbow replacement associated with wear.