Wear analysis of retrieved alumina heads and sockets of hip prostheses

Abstract

The wear behavior of hip prostheses alumina components was studied on 20 retrieved implants removed for socket loosening. The observed wear takes two forms: a running-in of the mating surfaces and a gross disruption of the surfaces. The running-in is very shallow, in the order of 0.2 micron after 8 years of implantation. This is observed on the load-bearing areas of the components. Gross wear is not material-related but had always been associated to a high contact pressure between the edge of the socket and the femoral head. Such a high contact pressure occurs after the socket had loosened and then tilted or if it was initially positioned too vertically. The long-term success of alumina-alumina THP components depends essentially upon biomechanical considerations and upon the quality of the material. The area of contact between the head and the socket should be large enough to minimize the contact stresses. This can only be achieved by a good positioning of the socket and by a close tolerance fit of the alumina components; any deviation from sphericity should also be avoided. The normal wear behavior of alumina is a running-in process leading to an average wear rate of 0.025 micron/year as compared to 100 microns/year for UHMWPE on metallic heads.

Risk of Impingement and Third-body Abrasion With 28-mm Metal-on-metal Bearings

“…There were also frequent reports of ''stripe'' wear across heads and around cup rims [15,54,62,71,77]. Our MoM retrieval studies noted similar stripe damage in retrieved MoM [6,9,10], although other groups disavowed their existence [34].…”

Ideal Femoral Head Size in Total Hip Arthroplasty Balances Stability and Volumetric Wear

“…[11] Further, at short term follow up (average 5 years), large head metal-on-metal THA has shown increase wear at the trunion-head interface and evidence of corrosion and fretting of the stem and head, which may lead to increase metal release into the body. [7,16] Ceramic-on-ceramic bearings, in general, are associated with lower wear rates compared to polyethylene [13,21]; however, microseparation during swing phase can result in stripe wear on the head and liner rim. [10] As with other bearing materials, larger head ceramic-on-ceramic THA would allow for increased impingement free range of motion and stability leading to potentially less stripe wear without the higher risk of volumetric wear seen with larger heads on polyethylene.…”

Factors Affecting Modular Acetabular Ceramic Liner Insertion: A Biomechanical Analysis

“…The extremely low wear of ceramic bearings has been documented extensively [5,6,8,11] and needs to be weighed against well-described disadvantages including fracture [3,8,9,13], audible squeaking [19,24], increased cost, and a reduced positional range of error during component implantation. Early ceramic fracture rates as high as 7.5% [3] have resulted in multiple mechanical property improvements, resulting in substantial increases in material strength and hardness and subsequent reduction in the incidence of ceramic fracture.…”

“…In vivo linear wear rates as low as 0.016 to 0.025 mm per year have been observed [5,6,11], which is approximately 4000 times less than with historical metal-on-polyethylene devices. Furthermore, the wear particles generated in a COC coupling are relatively bioinert [17,21].…”