Editorial “Mid-term results of the BIOLOX delta ceramic-on-ceramic total hip arthroplasty”

Historically, ceramic-on-ceramic (COC) articulations in total hip arthroplasty (THA) have been shown to have the lowest rate of wear and osteolysis (1). However, the use of COC bearings has been lessened by their risk of fracture, squeaking and revision surgery (2-4). As a result, in 2003, Ceramtec (Plochingen, Germany), the largest manufacturer of ceramic bearings in the world, introduced their 4th generation of ceramic components—Biolox Delta. This 4th generation ceramic is a zirconia toughened alumina ceramic designed to decrease the risk of fracture by incorporating yttria-stabilized tetragonal zirconia particles that prevent the initiation and propagation of cracks and strontium oxide that dissipate energy by deflecting cracks, and thereby increasing the strength and toughness. Lee et al. reported their mean 66.5 months follow-up of 286 hips prospectively followed after a THA with a 4th generation COC bearing (5). Specifically, they determined the rate of ceramic fracture, post-operative noise, mid-term results and survivorship in this cohort.

This study confirmed that the fracture rate is low with 4th generation COC bearings. Lee et al. reported no fractures of a ceramic head, but there was one case of an atraumatic fracture of the ceramic liner (0.3%) 10 months post-operatively. The authors acknowledged that the liner was incompletely seated on the postoperative radiograph. Failure to seat the liner can be dependent on the surgical technique. Lee et al. indicated that the acetabular components were “press-fitted”, but do not comment on the degree of press-fit. Press-fit acetabular components are susceptible to rim deformation and if the press-fit is very tight, it can deform the acetabular component significantly so that it is difficult to properly seat the very stiff ceramic liner (6). This can result in malpositioning of the liner and subsequent fracture. In a study with a longer follow-up of 6 years, Aoude et al. found no cases of ceramic fracture or chipping, and no revision surgery necessary for a complication related to the Biolox Delta COC bearing (7).

Since fracture has become an uncommon complication with 4th generation ceramic bearings, individual surgeon experiences do not provide a sufficient cohort of patients to truly understand the incidence of this complication. For this, large joint registries provide a better insight into the risk. Using data from the National Joint Registry (NJR) for England, Wales, Northern Ireland and the Isle of Man, Howard et al. indicated that incidence of fracture of a Biolox Delta head and liner was 0.009% (7/79,442) and 0.126% (101/80,170), respectively (8). Overall, they found that there is good evidence that the latest generation of ceramic has greatly reduced the odds of head fracture but not of liner fracture.

Although the etiology of squeaking in COC bearings is not well understood, it has been associated with poor lubrication, implant design, third body wear and implant positioning resulting in edge loading. The study by Lee et al. specifically addressed at the incidence and activity associated with noise generated by the COC bearing (5). Overall, 11.9% of the patients reported post-operative noise in their hip. Although there was no significant difference in the abduction of the acetabular components, hips with noise had a significantly greater anteversion of the cup than those hips that had no noise. This illustrates the sensitivity of COC bearings to implant orientation and the risk of neck-rim impingment. The 11.9% incidence is much higher than the incidence of squeaking of 4.2% reported by Owen et al. in their meta-analysis of 43 studies including 16,828 COC THAs (3).

Lee et al. reported that no hips had detectable wear, focal osteolysis or signs of loosening. All of the acetabular components and femoral stems were reported as having radiological evidence of bone ingrowth at final follow-up. However, radiolucent lines were noted around the Corail stem in Gruen zones 1 and 7 in 2.8% of the cases, which has been associated with femoral loosening with this particular stem—this is illustrated in figure 3 of the article, where the implant appears to have subsided between the 1- and 6-year radiographs. Unlike the Lee study with a small cohort of patients, other larger series from national databases have questioned the longevity of COC hips compared to metal-on-polyethylene (MOP) THAs. COC bearings have previously been shown in the Australian Registry to have higher revision rates due to dislocation when compared with MOP THAs (9). As well, Jameson et al. reported that in 35,386 THAs in the NJR with the same stem and cup, the overall 5-year revision was significantly higher in patients with COC bearings [COC, hazard ratio (HR)=1.55, P=0.003] compared to MOP bearing (4). Until longer-term data is available, the increased mid-term rate of revision with COC THAs and the decreased concerns about wear and osteolysis with cross-linked polyethylene, suggests that it might be prudent to target the use of COC bearings in younger patients.

The study by Lee et al., as well as the other studies specifically looking at the early and mid-term results of the 4th generation COC bearings, reassure the orthopaedic community that it is a reliable and safe bearing in patients undergoing THA. However, they also highlight the sensitivity of this bearing to implant positioning and surgical technique to avoid postoperative fracture and noise. Longer-term studies from the Registries remain crucial in determining the best patients for this technology and the ultimate risk of fracture.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: This article was commissioned and reviewed by the Executive Editor-in-Chief, Dongquan Shi, MD, PhD (Department of Sports Medicine and Adult Reconstruction, Drum Tower Hospital, Medical School, Nanjing University, Nanjing, China).

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at http://dx.doi.org/10.21037/aoj.2017.11.01). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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