THE USE OF CT IN PRE OPERATIVE ASSESSMENT OF FAILED TKR PRIOR TO REVISION SURGERY.

Abstract

Revision total knee arthroplasty (TKA) is becoming a more frequent procedure throughout Europe. Painful patello-femoral problems, patellar dislocation, impingement pain as well as aseptic loosening and gross malalignment are among many causes. We investigated the use of CT scans in identifying alignment causes for pain in failed TKA where no other obvious cause is found.

Twenty poorly functioning TKA were analysed using the Perth CT protocol. All patients were awaiting revision TKA and had no obvious evidence of infection or loosening. They were scanned using a GE multislice CT scanner. The measurements were performed using standard CT software. Knee society scores were obtained pre- and post-operatively.

The mean coronal position of the components was three degrees of valgus for the femoral component and 2.5 degrees of varus for the tibial component. Fourteen knees had errors of femoral component rotation, which ranged from one degree of external rotation to nine degrees of internal rotation. The cumulative error of implantation ranged from 6–24 degrees in all planes. Knee society scores improved post-operatively from a mean of 52 pre-operatively to 83 at one year. Compound error also improved to a range of 6 to 10 degrees in all planes.

Revision TKA remains a difficult procedure that is increasing in frequency. The use of a CT protocol allows all coronal, sagital and rotational errors of an implant to be accurately identified prior to surgery. This could be useful in the small groups of patients with painful TKA that have no obvious cause for failure. Total knee replacement failure in these cases maybe explained by a cumulative error in alignment and correction of which may improve their Knee Society Scores.

We believe that a CT scan of a failed TKA is useful as part of the pre operative planning and also in investigating painful TKA where no obvious cause is found.