The role of cone beam CT in the study of symptomatic total knee arthroplasty (TKA): a 20 cases report.

Objective: The aims of this study were to evaluate the efficacy of cone beam CT (CBCT) in the study of the patellar tilt angle and rotational alignment of the femoral/tibial component after total knee arthroplasty and to estimate how metallic artefacts impaired detection of periprosthetic bone structures and bordering tendon-muscle structures. Methods: 20 symptomatic total knee arthroplasties were examined using CBCT by three independent observers. The patellar tilt angle and rotational alignment of femoral and tibial components were measured in relation to the femoral flange, transepicondylar axis and tibial tuberosity, respectively. A four-score scale, ranging from "many metallic artefacts" (the structure cannot be identified) to "no metallic artefacts" (the structure can be perfectly identified), was used to judge every structure. Results: The patellar tilt angle and rotational alignment of the prosthetic components showed very high intra-and interobserver agreements (intraclass correlation coefficient values 0.895-0.975 and 0.891-0.948, respectively). Bone and tendon-muscle structures cannot be identified in the distal part of the femoral component, whereas they can be well identified in the proximal part of the femoral component and in the proximal/middle third of the tibial stem. Conclusion: CBCT was an effective tool, providing reproducible measurements of the patellar tilt angle and the rotational alignment of the femoral/tibial component. Furthermore, it allowed bone and tendon-muscle structures analysis with little impediments from metal artefacts. Advances in knowledge: CBCT allows easy and accurate measurements on the rotational axial plane, unburdened by image quality impairment due to metal artefacts.