Seating of ceramic liners in the uncemented trident acetabular shell: is there really a problem?

UNLABELLED: Concerns have been raised regarding the risk of incomplete seating of metal-backed ceramic liners in the Trident acetabular system. This prompted us to audit our series of primary and revision THAs. We retrospectively reviewed 68 patients (78 arthroplasties, 55 of which were primary and 23 revisions) using the Trident acetabular system between 2003 and 2007. Anteroposterior and lateral radiographs were reviewed independently by two specialist registrars and one consultant surgeon to look for incomplete seating. Six liners were seated incompletely, representing 8% overall. All unseated liners were in the primary group, representing 10% risk in this group, compared with 0% risk in the revision group. The incidence of malseating in our primary arthroplasty group was similar to the published incidence (16.4%). We encountered no problems in patients having a revision. We suspect shell deformation contributes to malseating of the metal-backed ceramic liners. To reduce the rate of malseating, we now underream by 0.8 mm rather than the usual 1.8 mm, particularly if the bone is sclerotic. LEVEL OF EVIDENCE: Level IV, case series. See the Guidelines for Authors for a complete description of levels of evidence.