Measuring tibial component rotation of TKA in MRI: What is reproducible?

Purpose: Correct rotational alignment of components is crucial for the success of total knee arthroplasty (TKA). Defining landmarks on the tibia that allow for reproducible measurement of component rotation seems to be more challenging than on the femoral side. This study compares the reproducibility of three different measurement techniques.

Scope: A magnetic resonance imaging (MRI) analysis of 55 patients following TKA was conducted. The rotation of the tibial components was determined using three different reference lines: a tangent to the posterior tibial margin, the tibial epicondylar axis, and the tibial tubercle. Data were analyzed for intra- and inter-observer reliability using intra-class correlation coefficients (ICCs), and a variance comparison between measurement techniques via F-test.

Results: Highest reliability and lowest variances for measurement of tibial component rotation were achieved by relation to the tibial epicondylar axis and posterior tibial margin. The tibial tubercle proved to be less reliable (ICC 0.632 (interobserver) and 0.526 (intraobserver)), and variances were significantly higher in comparison with the other two techniques.

Conclusion: Based on the presented MRI data, measurements of the tibial component rotation are done best using the posterior tibial margin and the tibial epicondylar axis. The tibial tubercle measurement proved to be less reliable for this purpose. We suggest that all three reference lines will be used for assessment of a painful knee following TKA to allow for informed decision making and for choice of best treatment options for the patient.