Relationship Between the Sagittal and Coronary Alignment of the Tibiofemoral Joint and the Medial Meniscus Extrusion in Knee Osteoarthritis

<b>Background/Objectives</b>: This study aims to clarify the reproducibility, validity, and accuracy of tibial external-rotation alignment evaluation using ultrasound imaging and to investigate the relationship between medial meniscus extrusion (MME) and tibiofemoral alignment in both the sagittal and coronal planes in knee osteoarthritis (OA). <b>Methods</b>: Study 1 included 10 healthy participants. The tibial external-rotation angle was calculated using MRI. In the ultrasound imaging evaluation, the differences in the distance from the most posterior points of the tibial and femoral condyles to the skin were calculated as the medial and lateral condyle gaps, respectively. The mediolateral (ML) gap was calculated by subtracting the lateral condyle gap from the medial condyle gap. Study 2 included 63 patients with unilateral OA and 16 healthy controls. MME was compared according to the severity of OA, the degree of tibial rotation, and the presence or absence of a tibial posterior shift. <b>Results</b>: Ultrasound imaging examinations showed high intra- and inter-rater reliabilities (0.786-0.979). The ML gap significantly affected the tibial external-rotation angle, determined using MRI. The ML gap of ultrasound imaging was significantly correlated with the ML gap of MRI. MME was significantly higher in the Early OA group than in the Control group. There was no significant difference in MME based on the tibial rotation degree. The group with a tibial posterior shift exhibited significantly more MME than that without a posterior shift. <b>Conclusions</b>: Ultrasound imaging is useful for evaluating knee alignment. MME was found to be associated with the tibial posterior shift.