297. NEW ALUMINA HEAD ON AN OLD MORSE CONE FOR UNIPOLAR REPLACEMENT TOTAL HIP ARTHROPLASTY

Abstract

Purpose of the study: Cementless stems completely coated with hydroxyapatite have confirmed long-term stability with 25 years follow-up for the oldest models (Furlong, Corail). Different bearings do not all have the same stability because of polyethylene wear debris. Unipolar replacements with a stable femoral implant raise the issue of changing the head on a used morse cone. Can a new alumina head be positioned on an old morse cone or must a metal head be used to avoid the risk of alumina fracture?

Material and methods: From 1993 to 2005, among the 228 revision hip prostheses in our centre, we reviewed retrospectively 79 unipolar replacements with implantation of a new ceramic head on a stable femoral implant (Corail). The other replacements were bipolar for 113 and unipolar with a metal head in 36. The reasons for the replacement were cup loosening (n=68), major polyethylene wear (n=11). Mean age was 71 years, 42 men for 37 women, mean time to reoperation 11 years (range 7–15). The stability of the femoral stem was examined on the intraoperative x-ray. The head was extracted with a mechanical extractor and the morse cone was protected throughout the operation. The quality of the titanium cone (12/14) was assessed visually as recommended by P. Hernigou (RCO 2003). Acceptable deterioration: intact cone or aspect of corrosion. Unacceptable deterioration: inclined cone, impacted cone, cone with wide truncation. A new alumina head was implanted on the cleaned, dry cone. The cup was replaced with a screwed socket (Tropic, Spirofit) and 64 polyethylene inserts for 15 alumina inserts.

Results: Sixty-one patients were reviewed. Seventeen patients died with no incident concerning the prosthesis; one patient was lost to follow-up. Mean follow-up since revision was nine years (range 2–15). Three cups were changed: two for recurrent dislocation and one for early migration, with a new head replacement. There were no head fractures and no cases of head decoaptation.

Conclusion: Although we have not had any incidents in this series, reimplantation of a new alumina head on an old morse code is not recommended by the manufacturers; but it is not prohibited if the cone is not macroscopically worn and remains clean and dry at reimplantation of the head. We now use alumina heads with an integrated 12/14 titanium sleeve. These sleeves need to be validated in the long term, but at the present time allow us to use large heads and an alumina-alumina bearing.