Tibial component rotation assessment using CT scan in medial and lateral unicompartmental knee arthroplasty

Background: Rotation of tibial component has not been analysed in literature for unicompartmental knee arthroplasty. The purpose of the study was to determine and compare the rotation of medial and lateral unicompartmental knee arthroplasty (UKA) tibial components. We assumed both components (lateral and medial) were positioned with external rotation. Patients and methods: Eighteen lateral and 19 medial UKA patients were scanned postoperatively in neutral position with computed tomography enabling lower extremity three-dimensional image acquisition from the hip to the ankle. All the patients were operated by three different senior surgeons using the same surgical technique. From the reconstructions we measured the two-dimensional (2D) rotation of the tibial components. Results: The rotation of the tibial component was external (mean 6.5 degrees, SD 5.1 degrees) for the medial UKA and external (mean 7.3 degrees, SD 10.3 degrees) as well for the lateral UKA. The difference was statistically insignificant (P=0.717). Discussion: This study presents the first 2D in vivo analysis accurately determining and comparing medial and lateral UKA component rotation. Despite a wide range of value, we found both components were indeed externally rotated. The variability in implant positioning was observed despite the rigorous performance of an experienced surgeon using routine techniques in patients selected under routine criteria. Further analysis of these patients for satisfaction and implant survivorship in relation to implant rotation may give us an optimal range for the tibial component. If it is found that this ideal range cannot be consistently obtained with current surgical techniques then there may be a case for the use of a navigation system.