The location of the popliteal artery in extension and 90 degree knee flexion measured on MRI.

We measured the location of the popliteal artery (PA) in extension and 90 degree of knee flexion by magnetic resonance images (MRI) to provide practical information to avoid PA injury. The MRIs of 30 knees of Korean male subject whose mean age was 20.7 were acquired in knee extension and 90 degree flexion. The distance from the posterior aspect of knee joint to the PA was measured at three levels on the axial images and one sagittal image. At the joint line level, the PA was located lateral to the PCL 2.4 mm in extension and 3.2 mm in flexion (p=0.247), and 3.9 mm in extension and 7.6 mm in flexion from the posterior capsule (p<0.001). At 1 cm distal to the joint line, it is 2.7 mm in extension and 7.2 mm in flexion (p<0.001), and at 2 cm distal to the joint line, 4.9 mm in extension and 9.7 mm in flexion from the posterior tibial cortex (p<0.001). In sagittal plane, the nearest distance between PA and posterior tibial cortex was 1.8 mm in extension, and 6.2 mm in flexion (p<0.001). The PA was located around 3 mm lateral to the PCL, and within 5 mm in extension and 10 mm in 90 degree flexion of the knee behind knee joint. It moves farther posteriorly in 90 degree flexion than in extension of the knee. The conventional wisdom of flexing the knee to prevent the PA injury was supported by this study.