Background: Internal-external (I-E) malrotation of the tibial component is associated with poor function after total knee arthroplasty (TKA). Kinematically aligned (KA) TKA uses a functionally defined flexion-extension (F-E) tibial reference line, which is parallel to the F-E plane of the extended knee, to set I-E rotation of the tibial component. Methods: Sixty-two, three-dimensional bone models of normal knees were analyzed. We computed the bias (mean), imprecision (± standard deviation), and limits of agreement (mean ± 2 standard deviations) of the angle between five anatomically defined tibial reference lines used in mechanically aligned (MA) TKA and the F-E tibial reference line (+ external). Results: The following are the bias, imprecision, and limits of agreement of the angle between the F-E tibial reference line and 1) the tibial reference lines connecting the medial border (- 2° ± 6°, - 14° to 10°), medial 1/3 (6° ± 6°, - 6° to 18°), and the most anterior point of the tibial tubercle (9° ± 4°, - 1° to 17°) with the center of the posterior cruciate ligament, and 2) the tibial reference lines perpendicular to the posterior condylar axis of the tibia (- 3° ± 4°, - 11° to 5°), and a line connecting the centers of the tibial condyles (1° ± 4°, - 7° to 9°). Clinical relevance: Based on these in vitro findings, it might be prudent to reconsider setting the I-E rotation of the tibial component to tibial reference lines that have bias, imprecision, and limits of agreement that fall outside the - 7° to 10° range associated with high function after KA TKA.
Brar, A. S., Howell, S. M., & Hull, M. L. (2016). What are the bias, imprecision, and limits of agreement for finding the flexion-extension plane of the knee with five tibial reference lines? Knee, 23(3), 406–411. https://doi.org/10.1016/j.knee.2016.01.005