Sleeved heads recommended for revision
The use of ceramic ball heads with titanium alloy sleeves helps to reduce the risk of adverse local tissue reactions (ALTR) without compromising the ceramic head’s strength and the corrosion resistance of the modular junction. Koch et al. came to this conclusion after analyzing 24 retrieved hip implants with BIOLOX®OPTION sleeved ceramic ball heads. The sleeve allows using a ceramic head on the used taper of a stem remaining in situ at revision that, without sleeves, could exert an inappropriate load on the female taper.
The ball head’s inner taper was graded by a metal transfer scoring system. Fretting and corrosion of the titanium sleeves’ inner and outer surfaces were evaluated by the Goldberg scale. The retrieved components showed little mechanical or corrosive damage. The mean fretting score was 1.8 for the inner and 1.2 for the outer sleeve surface. The mean corrosion score was 1.8 for the inner sleeve; no corrosion was observed on the outer surface. The magnitude of fretting corrosion was not correlated to stem material. The mean metal transfer score of 2.3 was similar to the findings of a previous retrieval study performed by the authors with BIOLOX®forte heads.
14 primary and 10 revision implants were revised and retrieved at the Hospital of Special Surgery in New York. The reasons for the revisions were not trunnion- or ball head-related. The mean implantation time had been 15.5 months, the mean patient age was 61.1 years. 15 femoral stems were made of titanium alloy, 6 of CoCr and 3 of TMZF.
AAHKS 2017 update on fretting corrosion
At the 2017 Annual Meeting of the American Association of Hip and Knee Surgeons, Berry moderated a symposium dedicated to “The ‘New Disease’: Taper Corrosion”. Metal levels are the cornerstone of diagnosis: with a well-functioning MoP bearing, they should be lower than 1ppb in the blood/serum, said Della Valle. He recommended to make sure that the taper is dry and that a metal head is impacted (“hit hard”) with enough force for preventing fretting corrosion. Jacobs noted that existing data show a variation in prevalence by year of surgery between 0% and 10.5%. The implant-related factors are head size, taper geometry, taper tolerances, surface finish, flexural rigidity, material composition, metallurgy and multiple metal-metal contacts. He put up the question if cobalt alloy heads and stems should not be abandoned altogether. Bolognesi found sleeved ceramic ball heads for revision probably the best available option, pointing out that the majority of high-volume revision surgeons uses them. He urged to cleanse the taper with great effort and care. Mabry gave these recommendations for prevention: revise any component malposition, maximize femoral-head diameter, consider using dual mobility bearings, and lower the threshold for constrained liners.
Reasons for revision in THA
Sleeves well tolerated
Patients with large-diameter sleeved ceramic ball heads have elevated titanium levels in the blood, but this has no clinical consequence. Deny et al. compared whole blood Ti levels at minimum 1-year follow-up in patients who had received sleeved 44–48mm heads and patients who had received 36–40mm heads without sleeves. There were no signs of adverse reactions to metal debris (ARMD) in either group, and the clinical results were similar.
Second PJI Consensus Meeting
The Second International Consensus Meeting on Prosthetic Joint Infection (ICM) will be held in Philadelphia (USA) on July 25–27, 2018. The steering committee of Javad Parvizi and Thorsten Gehrke has brought together a faculty of over 800 renowned experts in the field who agreed to serve in the convention. Its aim is to develop a consensus document outlining treatment options for infection patients.
How to reduce fretting corrosion
Avoid using ball heads with high lateral offset; retain macroscopically undamaged stems at revision; pay particular attention to the progression of fretting corrosion as well as to the special risks associated with heavy and active patients. Wight et al. give these recommendations on how to mitigate fretting corrosion on the basis of a systematic literature review including 91 articles.
When using metal ball heads, these should have a small diameter and not be made of cast alloy. In this case, the combination with stems of low flexural rigidity should also be avoided. However, according to the authors, there is fair evidence to prefer the use of ceramic or ceramicised metal rather than metal ball heads to mitigate the risk fretting corrosion.