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

Abstract

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. 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 1cm 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. 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 ± 17.9years and 41.1 ± 18.8years, 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. 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 III, retrospective case-control study.