INVESTIGATION OF MACRO- AND MICROSTRUCTURAL DIFFERENCES IN COMMERCIALLY AVAILABLE RESURFACING HIP IMPLANTS.

Abstract

Resurfacing hip implants differ in macro- and microstructure. Manufacturing related parameters like clearance or carbon content influence the wear behaviour of these metal-on-metal bearings. The aim of this study was to analyse the main macro- and micro-structural differences of commercially available resurfacing hip implants.

Ten different commercially available resurfacing hip implant designs were included in this investigation:

• - BHR^® (Smith& Nephew/MMT)

• - Durom^® (Zimmer)

• - Conserve Plus^® (Wright Medical)

• - Cormet^® (Corin)

• - Icon^® (IO)

• - ReCap^® (Biomet)

• - Adept^® (Finsbury)

• - ASR^® (DePuy)

• - BS^® (Eska)

• - Accis^® (Implantcast).

The heads and cups were measured in a coordinate measuring machine and radial clearance as well as sphericity deviation were calculated. Surface roughness measurements were carried out. The microstructures of the heads and cups were inspected using SEM and element analysis was performed using EDX to identify carbides and the alloy composition.

The mean radial clearance was found to be 85.53 μm. The range was from 49.47 μm (DePuy, ASR^®) to 120.93 μm (Biomet, ReCap^®). All implants showed a sphericity deviation of less than 10 μm. The highest sphericity deviation was found to be 7.3 μm (Corin Cormet^® head), while the lowest was 0.8 μm (Smith& Nephew BHR^® head). On average, the heads tended to have a higher sphericity deviation (4.1 μm, SD: 2.3 μm) compared to the cups (2.7 μm, SD: 1.4 μm). SEM revealed that most manufacturers use a high carbon alloy casting manufacturing process combined with heat treatment after casting (Corin Cormet^® and Wright Conserve^®: head and cup; DePuy ASR^®: cup; Eska BS^®: head).

Commercially available resurfacing hip implants differ in design and manufacturing parameters, including macro- and microstructure, which are critical in achieving low wear and ion release. This study was designed to aid in the understanding of clinical observations. Also, specific information is now available for surgeons choosing an implant designs.