What Is the Frequency of Fracture of Ceramic Components in THA? Results from the Norwegian Arthroplasty Register from 1997 to 2017
Authors: Hallan Geir , Fenstad Anne Marie , Furnes Ove 
Published: April 2020

Abstract

Background
Ceramic bearings in THA have been used to reduce wear and, more recently, to avoid metals in the bearing because of the risk of metal ions adverse effects. Potential disadvantages to ceramic bearings are their brittleness and the ceramic fracture risk, which may lead to revision surgery. The frequency of revision for a fracture ceramic bearing, however, has not been thoroughly studied.

Questions/purposes
(1) What is the frequency of revision for a fractured ceramic bearing in ceramic-on-polyethylene (CoP) and ceramic-on-ceramic (CoC) THAs, and is there any difference between alumina ceramics and alumina matrix composites (AMC)? (2) What are the factors associated with this complication? (3) To what extent did the patients who underwent revision for a fractured ceramic bearing undergo subsequent revisions, and for what reason?

Methods
The Norwegian Arthroplasty Register has collected data on hip arthroplasty since 1987 and has a completeness of reporting of 97.3% for primary THAs and 93.3% for revision. From 1997 to 2017, 146,171 primary THAs were registered in the Norwegian Arthroplasty Register. Of these, 31,479 had a CoP articulation and 5790 had a CoC articulation. Two manufacturers produced ceramic heads; one produced 25,678 alumina heads and the other made 2465 alumina heads. All 7901 AMC heads were made by the same manufacturer. Patients who underwent CoP THA were a median (range) of 63 years old (11 to 98) and CoC THA were a median (range) 61 years old (17 to 95); 38% (11,833 of 31,479) of the patients who underwent CoP THA and 41% (2379 of 5790) of the patients who underwent CoC THA were males. Femoral heads made of alumina (n = 28,143), zirconia (n = 1225), and AMC (n = 7901) ceramics were used. To assess revision frequency, we identified patients who underwent revision because of fracture of a ceramic head and/or liner, and calculated the Kaplan-Meier survivorship free of revision for fracture in CoC and CoP articulations. Alumina ceramics and AMC were compared. In terms of factors potentially associated with revision, patient factors (age, sex, and diagnosis), type of articulation (CoP or CoC), femoral head size, and femoral head/neck length were evaluated with Cox regression models to evaluate any association with ceramic fracture and a Poisson regression to compare alumina and AMC head fractures. To evaluate subsequent revisions, hips that were revised for ceramic fracture were evaluated for any further revisions; Kaplan-Meier survivorship free of further revisions was calculated, and revision causes were identified.

Results
Survivorship free from revision for ceramic fracture was 99.9% (95% CI 99.9 to 99.9) for CoP bearings, and 99.8% (95% CI 99.6 to 100) for CoC bearings at 10 years, with 7467 and 1884 hips at risk in the two groups, respectively. The hazard ratio for ceramic head fracture was 3.6 (95% CI 1.7 to 7.6) for CoC compared with CoP. The risk of fracture was greater for alumina ceramics than for AMC heads (adjusted HR 14.1 [95% CI 4.2 to 47.0]; p < 0.001). Factors that were associated with revision for fracture of a ceramic head were male sex (HR 5.2 [95% CI 2.6 to 10.4]; p < 0.001), a CoC articulation compared with CoP (HR 3.6 [95% CI 1.7 to 7.6]; p = 0.001), a 28-mm femoral head compared with a 32-mm head (HR 2.7 [95% CI 1.1 to 6.4]; p = 0.02), and short head/neck length compared with a medium head/neck length (HR 2.5 [95% CI 1.1 to 5.3]; p = 0.03). Five of 50 patients undergoing revision for ceramic fracture underwent further revisions, resulting in a 5-year survivorship free from re-revision of 86% (95% CI 74.4 to 98.0). The reasons for re-revision were infection (n = 2), another ceramic head fracture (n = 2), and cup loosening (n = 1).

Conclusions
Fracture of a ceramic THA bearing is rare and seems to affect about one in 1000 patients who receive such a bearing. To minimize the risk of this complication, surgeons should avoid small femoral heads (< 32 mm) and the shortest head/neck lengths. Surgeons should also know that the risk is increased in CoC articulations and in males. Bearings made of AMC appear to be at lower risk than those made from alumina ceramics. However, the long-term clinical wear performance of AMC bearings has not been extensively studied and should be studied further.

Level of Evidence
Level III, therapeutic study.