Abstract
Introduction: We describe a CT method that allows the seven alignment characteristics of a knee arthroplasty to be defined in a single investigation.
Method: A multislice CT scanner, scans in 2.5mm slices from the acetabular roof to the dome of the talus with the legs in a standard position.
The mechanical and anatomical axes are identified, from 3 dimensional landmarks, in both AP and lateral planes. The coronal and sagittal alignment of the pros-theses is then measured against the axes.
The rotation of the femoral component is measured relative to the transepicondylar axis. Tibial rotation was measured with reference to the posterior tibial condyles and the tibial tuberosity. Coupled femorotibial rotational alignment was assessed by superimposition of the femoral and tibial axial images.
The results of 100 scans show a low inter and intra observer error rate whilst independent assessment shows a mean measurement error of 3mm in a three dimensional plane. The radiation dose is 2.7mSV.
Conclusions: The technique provides the only currently available measure of all the alignment characteristics required to assess the quality of a knee arthroplasty. It will become a gold standard in planning revision surgery and provide a valuable tool in assessing alignment of painful knee replacements.
The abstracts were prepared by Mr Roger Smith. Correspondence should be addressed to him at the British Association for Surgery of the Knee, c/o BOA, Royal College of Surgeons of England, 35–43 Lincoln’s Inn Fields, London WC2A 3PN.
