Purpose: Fracture of alumina implants is a rare cause of total hip arthroplasty (THA) failure. Over the last twenty years, improvement in the design of ceramic implants has helped reduce this risk. We observed five cases of alumina implant fracture over the last year. The purpose of this work was to analyse these recent events and to examine our experience to search for an explanation.
Material and methods: Between 1976 and 2002, eleven patients, five women and six men, mean age 57 years (range 32–87 years) required revision surgery for fracture of an alumina component. The time interval from primary surgery to revision was 36.5 months (range 7 – 106 months). An alumina-alumina couple was involved in nine cases and an alumina-PE couple in two. The primary THA used a press-fit metal backed alumina cup for five hips, a cemented alumina cup for three hips and a massive press-fit alumina cup for one. The alumina head measured 32 mm for ten hips, 22.2 mm for one. The femoral stems were cemented in seven cases, and hydroxyapatite surfaced in four. The acetabular component was involved in four cases and the femoral head in seven.
Results: Identified causes of ceramic implant fracture were: high-power trauma (insert) (n=1), insufficient head diameter (n=1), and defective head match (n=1). For the eight other fractures, involving three insets and five heads, no triggering factor could be identified. The three insert fractures involved two 50-mm cups and one 52-mm cup. Insert design had been changed before these fractures. Mean time from insertion to fracture was 12 months (range 8.5–15 months) in these cases.
Discussion: To our knowledge, all reported cases of ceramic implant fracture have concerned the prosthetic head. The present series demonstrates a recent development, fracture of acetabular implants. It is hypothesised that these fractures could be explained by an insufficient cup diameter associated with a recent change in the design of the metal-backed flush ceramic insert. These inserts have been modified and now have an “overhang” design associated with a thicker layer of ceramic for the smaller cup diameters. These accidents remain rare but justify careful surveillance, particularly during the first postoperative year.
