Abstract
Non-seated ceramic inserts have recently been identified as a common phenomenon in one popular modular ceramic system (16.4% of cases in Langdown et al. 2007. JBJS 89B (3):291–295). A preliminary audit at Tauranga Hospital demonstrated the same issue. However, most X-rays didn’t allow confirmation or exclusion of the problem.
A preliminary review of post-operative films of patients receiving modular ceramic acetabular implants at Tauranga Hospital was undertaken. A radiolucent jig was constructed to take images of three different modular ceramic acetabular systems. Images isocentered on the implants (seated & non-seated) were taken with variation in view given of the cup (rotation and plane of the X-ray beam relative to the implant face). Registrars & consultants were tested on their ability to detect non-seating on these images.
Two out of three acetabular systems showed non-seating in patients. Most films reviewed did not allow definitive decisions to be made about ceramic insert seating. The true incidence of non-seating in the arthroplasty population receiving modular ceramic implants is thus unknown. The images of the three systems taken in the radiolucent jig show the ability to detect non-seating is multifactorial. Implant specific differences in the shell and liner systems radiologic profile influence detection and education of surgeons may improve the chances of detection. The presence of the head of the femoral component limits detection of non-seating. The plane of the X-ray beam relative to the face of the cup along with the rotation of the non-seated region relative to the beam strongly influence detection. The plane of the X-ray beam relative to the face of the inserted acetabular component can be altered in post-operative films.
Typical post-arthroplasty hip films fail to consistently identify the occurrence of non-seating of modular ceramic acetabular inserts. Suggesting the true incidence remains unknown. Standard post-operative imaging needs to change to be confident of exclusion of this phenomenon in patients receiving modular ceramic implants.
Correspondence should be addressed to Associate Professor N. Susan Stott, Orthopaedic Department, Starship Children’s Hospital, Private Bag 92024, Auckland, New Zealand.
