This implant seemed to overcome the failings of previous designs. It is a ceramic bearing screwed into a titanium screw, which bonded to bone. The bearing surface was also coated with calcium phosphate to enhance secondary stability.

An initial study examined 40 patients over three years. No patients had any loosening, screw breakages, fractures, or local osteoporosis. The patient satisfaction was good with only two dissatisfied. On the basis of this, Orthosonics introduced it to the UK in 1999. Following problems with the device we conducted a survey with Orthosonics and the MDA.

In total 160 implants were implanted by 46 surgeons. We received replies from 33 surgeons representing 119 patients. There were 93 implants with a successful outcome but 17 had failed and been revised. The commonest mode of failure was osteolysis secondary to metallic wear debris. Also six implants showed radiographic loosening with symptoms, but had not been revised. There were three that showed radiographic loosening, but were symptom free.

A failure rate of 19% at one year is unacceptable. We are of the view that products of this type should be introduced in a controlled fashion as part of a prospective trial.