Difference in Rotational Alignment of the Tibial Component, as Determined by the Range-of-Motion Technique and Akagi's Line, is Influenced by Tibial Varus Deformity: A Cross-Sectional Study.

Background: Anatomical landmarks and range-of-motion (ROM) techniques are commonly used to rotationally align the tibial component in total knee arthroplasty (TKA). This study investigated; 1) the difference in tibial rotational alignment between the ROM technique and Akagi's line, 2) the influence of preoperative deformity and intraoperative gaps on this difference, and 3) intraoperative tibial rotational kinematics associated with these 2 techniques.

Methods: Patients who underwent cruciate-substituting (CS) TKA (Evolution, Microport Orthopedics) for knee osteoarthritis were enrolled. Intraoperatively, the rotational alignment of the tibial component was determined with the ROM technique and recorded. The difference from the value determined using Akagi's line was evaluated. Correlations among preoperative coronal deformity, postoperative coronal alignment, and intraoperative gaps between the femur and tibia were evaluated. Differences in knee kinematics (rotational movement of the tibia against the femur) between the 2 techniques were compared.

Results: This study included 34 knees from 34 patients. The rotational alignment of the tibial component using the ROM technique was 2.5±6.4° externally rotated in relation to that determined using Akagi's line (p=0.029), which was increased in knees with a smaller preoperative medial proximal tibial angle (r=0.45). Tibial rotational kinematics did not significantly differ between the 2 techniques.

Conclusions: The ROM technique and Akagi's line yielded significantly different values for the rotational alignment of the tibial component. Orthopedic surgeons using Evolution (CS) should be reminded that in knees with proximal tibial varus deformity, the ROM technique will result in external rotation of the tibial component in relation to Akagi's line.