Abstract
Introduction: We investigated the routine use of CT scans in identifying alignment causes for failure as well as in the pre operative planning of the procedure.
Methods: Twenty poorly functioning total knee arthroplasties were analysed using the Perth CT protocol. All patients were awaiting revision total knee arthroplasty and were scanned using a GE multislice CT scanner. The measurements were performed using standard CT software. Knee society scores were obtained pre- and post-operative.
Results: The mean coronal position of the components was 3 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 1 degree of external rotation to 9 degrees of internal rotation. Nine knees had errors of tibial baseplate rotation with all being internally rotated relative to the PCL/Tibial tuberosity axis from 3 to 12 degrees.
The cumulative error of implantation ranged from 6- 24 degrees in all 7 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 in all 7 planes.
Conclusions: Revision total knee arthroplasty remains a difficult procedure but is increasing in frequency. The use of a CT protocol allows all coronal, sagittal and rotational errors of a previous implant to be accurately identified prior to surgery. We believe that all knee revision operations should have a CT scan as part of the pre operative planning. Also CT scans may be useful in investigating painful total knee replacements. Total knee replacement failure in some cases maybe explained by a cumulative error in alignment when no other obvious cause is found.
Correspondence should be addressed to Mr Tim Wilton, BASK at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
