Fig. 2

The three methods used for the measurement of PTS as the cosine angle formed by the tangent to the medial tibial plateau (Line a) and perpendicular to each reference axis. A aPTS: the angle between lines a and b. B mPTS: the angle between line a and c. C pPTS: the angle between line a and d. a = tangent line to the medial tibial plateau, b = line connecting two points 5 cm and 15 cm distal to the knee joint on the anterior cortical line of the proximal tibia, c = line connecting two points 5 cm and 15 cm distal to the knee joint on the midpoint of the anterior/posterior cortical surface of the proximal tibia, d = line connecting two points 5 cm and 15 cm distal to the knee joint on the posterior cortical line of the proximal tibia. PTS = posterior tibial slope, aPTS = anterior PTS, mPTS = middle PTS, pPTS = posterior PTS