The Line Connecting The Anterior And Posterior Cruciate Ligaments Relationship With The Transepicondylar Axis

Background:Malrotation of the femoral and tibial components in total knee arthroplasty(TKA) is closely related to anterior knee pain, patellofemoral problem, joint stiffness, and polyethylene wear, which eventually requires revision. TEA has been widely accepted as femoral rotational reference,because it has been shown to be optimal or approximate to the flexion axis.Rotational orientation of the femoral component has been well established. Many methods had been proposed to determine the AP axis of tibial component. Common used methods include the tibial posterior condylar line(PC line),the medial third of the tibial tubercle, Akagi’s line,and the midsulcus of the tibial spine.A radiographic and anatomic study by Elias et al. showed that the anterior cruciate ligaments(ACL) and the PCL also participated in TEA formation, cooperating with medial and lateral collateral ligaments. This was also supported by Eckhoff et al. A cadaveric research of Fukubayashi et al. showed that cutting the ACL or PCL would have an effect on internal or external rotation of tibia, also supported by other studies. All Abovementioned studies indicate that ACL and PCL have close relationship with TEA, and probably functionto determine the rotation orientation of the tibia by an isometric mechanism. If this is not taken into consideration, ACL and PCL will certainly impinge on the intercondylar notch, and it will not be an isometric structure during the knee flexion. The relationship between the line connecting the midpoints of the anterior and posterior cruciate ligament(ACL and PCL, APCL line) and the transepicondylar axis(TEA)in normal healthy Chinese was unknown.Objective:The purpose of this study was to determine the relationship between the line connecting the midpoints of ACL and PCL(APCL line) and the TEA in normal healthy Chinese, as well as the comparison with other rotational lines by using three-dimensional(3D) measurements of computer tomography(CT) and MRI data.Methods:17 male and 15 female healthy Chinese volunteers were involved.None of them has knee disease. Three-dimensional(3D) surface models of each left knee were reconstructed from computer tomography(CT)and magnetic resonance imaging(MRI) respectively. 3D contours of the attachments of ACL and PCL, the medial and lateral collateral ligament(MCL and LCL) were reconstructed from MRI, and were labeled onthe3 D models of CT by using an iterative closest point algorithm. The APCL line, the tibial posterior condylar line(PC line), the medial third of thetibial tubercle(1/3 line), the Akagi’s line, and the midsulcus of the tibial spine(Midsulcus line), the clinical and surgical TEA(CTEA and STEA)were determined. And then, the paired intersection angles of them were measured.Results:the mean angle CTEA with APCL line, Akagi’s line, Midsulcus line,1/3 line,and PC line, respectively, was 90.25o ± 2.87o, 95.02o ± 2.97o,93.96o ± 3.93o, 102.38o ± 2.70o, and 87.13o ± 3.04o. The APCL-CTEA was significant different than other angles(p < 0.001). The mean angle STEA to the above lines, respectively, was 94.79o ± 3.09o, 99.43o ± 3.12o,98.45o ± 3.98o, 106.88o ± 2.85o, 91.63o ± 3.22o. The PC line-STEA was significant different than other angles(p < 0.05).Conclusion:We demonstrated that the APCL line was the closest perpendicular to the CTEA in normal Chinese subjects comparing with other rotational lines. Identifying the appropriate tibial plateau rotational orientation would be helpful to the posterior sloped cut and the tibial baseplate implant.