Is the Akagi Line a Reliable Landmark for Adjusting the Rotational Axis of the Tibial Component in Patients with Patellofemoral Instability?

ABSTRACT

Purpose: This study aimed to investigate whether the Akagi line is a reliable anatomic landmark for adjusting the rotational axis of the tibial component in patients with patellofemoral (PF) malalignment. Materials and methods: This retrospective case-control study included 86 patients with PF instability and 129 controls. On the superimposed axial CT images, TT-TG, TT-PCL, nTT-TG, nTT-PCL, knee joint rotation, and the angle between the Akagi line and surgical transepicondylar axis (Akagi/sTEA angle) were measured. In addition, a modified Akagi line, drawn 1 cm medial to the patellar tendon attachment, was defined, and the angle between the new Akagi line and sTEA (mAkagi/sTEA angle) was also measured and compared between groups. Results: There were 86 patients (47 females, 39 males) in the case group and 129 patients (56 females, 73 males) in the control group with a mean age of 35.7 ± 17.9 years and 41.1 ± 18.8 years, respectively (p < 0.001). Radiologic variables of PF alignment (TT-TG, TT-PCL, nTT-TG, nTT-PCL, and knee joint rotation) were significantly abnormal in the case group (p < 0.001 for all variables). The Akagi/sTEA angle was significantly higher in the case group, resulting in 89.5% external malrotation of the tibial component (> 10°). However, the tibial component was 96.5% aligned correctly (between 10° external and 3° internal rotation) in the control group. Using the modified Akagi line significantly improved the rotational alignment, and normal tibial rotation increased to 93.3% of the case group. The Akagi/sTEA angle strongly correlated with the knee rotation (rho 0.735, p 0.001), TT-TG (rho 0.715, p 0.001) and nTT-TG (rho 0.783, p 0.001). But the TT-PCL (rho 0.459, p 0.001) and nTT-PCL (rho 0.589, p 0.001) had a medium correlation. Conclusions: The Akagi line might cause unacceptable external rotation of the tibial component in patients with PF malalignment. The use of the modified Akagi line described in this study may be a solution for the rotational mismatch between femoral and tibial components in TKA. Level of evidence Level III, retrospective case-control study.