Abstract
This paper details a novel method to characterize and quantify edge wear patterns in ceramic-on-ceramic acetabular liners using a roundness measurement machine to measure the post-wear surface. A 3D surface map is produced which encompasses the measured surface covering the wear patch, the uncontrolled edge geometry and form of the bearing surface. The data is analysed to quantify linear penetration and volume. The developed method was applied in a blind study to a set of six 36mm ceramic-on-ceramic acetabular cup liners that were measured and analysed to characterise the edge wear. The in-vitro linear wear penetration ranged from 10μm to 30μm. The computed volumetric wear results obtained from the blind roundness measurement study were compared against the measured gravimetric results indicating a strong correlation between the results (0.9846). This study has also highlighted that measured liners exhibited an area of localised edge wear locates above the bearing surface as well as a smearing effect on the bearing surface caused by debris from edge wear. A study was carried out to test the repeatability of the measurement method and the inter-operator variability of the analysis. The results of the study show a standard deviation for the entire measurement and analysis process of 0.009mm3 for first user and 0.003mm3 for second user over twenty datasets. Hence the method displays high repeatability of the measurement and analysis process between users. This method allows for the delineation of form and wear through the determination of local geometry changes on what is essentially a freeform surface. The edge geometry is only partially controlled from a GD&T perspective and its geometry relative to the bearing surface varies from part-to-part. This method whilst being subjective allows for the determination of wear in this area with a high level of repeatability. However the limitation of this method is that it can only measure 5mm wide band of the liner due to the limited gauge travel range of 2mm
Highlights
The life expectancy of a hip prosthesis is commonly expected to be 15–20 years
The use of fourth generation ceramic-on-ceramic bearings have proved to be very efficient and has grown in popularity for primary hip surgery in the last decade [1]. This is due to the low reported wear volumes associated with all ceramic bearings [2] as well as the fact that ceramic debris being bio-inert overcomes the commonly reported issues of systemic cobalt chromium ion concentration as reported in metal-on-metal bearings [3,4] and issues of osteolysis induced by polyethylene wear debris in n Corresponding author
The paper details a novel method for characterising edge wear in ceramic-on-ceramic acetabular liners and quantifying wear volumes in the transition area between the bearing surface and outer geometry
Summary
The life expectancy of a hip prosthesis is commonly expected to be 15–20 years. In the UK during the last decade 711,765 primary surgeries have been carried out in comparison to 80,042 revision surgeries [1] to replace joints that have failed either prematurely or at the end of their useful life. The use of fourth generation ceramic-on-ceramic bearings have proved to be very efficient and has grown in popularity for primary hip surgery in the last decade [1]. From previous simulator studies it has been observed that levels of wear in ceramic-on-ceramic bearing surface can be of the order of 0.2 mm3/million cycles [2] With such excellent material properties and high survival rates, ceramic-on-ceramic hip prosthesis has been widely implanted into ever younger, more active patients [10,11,12], and yet very few long term large set retrieval studies have been carried out due to the survivorship of the implants [13,14,15]. Ceramic-onceramic hip prosthesis are reported to squeak in-vivo [19,20]
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