Abstract
Ceramic-on-ceramic (C-C) total hip replacements (THRs) are an attractive option for young, active patients [1, 2]. However, more clinical data is necessary to establish the reasons of failure of contemporary C-C THRs in vivo. The objective of the present study was to assess the surface damage on retrieved C-C THRs and determine possible influential factors that may explain their in vivo performance. Thirty-five C-C retrievals of material type Biolox® forte (n=28) and Biolox® delta (n=7) (CeramTec AG, Plochingen, Germany) were collected after a mean of 3.7 ± 3.2 years in vivo. Semi-quantitative surface damage assessment [3] was performed on all retrievals to obtain both a damage score (DS) (Fig. 1). Contact profilometry was performed on the retrieved femoral heads to characterize the type of surface damage (metal transfer, stripe wear). Scanning electron microscope (SEM) images were obtained from two femoral heads displaying areas of typical surface damage. The implantation period correlated with the damage score (DS) of the femoral heads (R=0.573, p<0.001) and the acetabular cups (R=0.592, p<0.001). However, the metal transfer DS of the femoral heads did not correlate with implantation period (R=0.185, p=0.29). Surface roughness of metal-transfer areas were positively skewed (additive metal transfer) while the stripe damage areas were negatively skewed (grain removal), as evidenced by SEM analysis. Stripe damage was observed on both the Biolox® forte and Biolox® delta retrieved femoral heads; however, the extent of grain removal appeared less severe on the Biolox® delta retrieved femoral heads due to their overall smaller grain size (Fig. 2). Inclination angles > 45° was associated with a greater DS rate [DS/time of implantation], which had also been suggested elsewhere [4]. Four patients reported squeaking in their C-C THRs; one of which was a 54 yr-old male patient who completed three full marathons with his implant. In this his case, the DS for this retrieval was below average, with metal-transfer being the only macroscopic damage feature. Fracture of the acetabular liner occurred in three patients, all of which had malpositioned components. Metal-transfer on the ceramic surface could possibly cause a local break down of the fluid film and may facilitate, in addition to an increased inclination angle, stripe damage via an adhesive wear mechanism. Therefore, direct contact between the Ti-alloy acetabular shell and the ceramic femoral head should be avoided at primary surgery. C-C THRs remain an attractive option for young, active patients, but care must be taken during implantation to appropriately position the acetabular cup and to avoid unwanted metal-transfer as such alteration at the bearing interface may change implant tribology.
