Fig. 2

Triangle zone—the medial and inferior low risk zone of the IPBSN is a triangle that a vertical line is projected downward from the medial edge of the tibial plateau and a horizontal line from the tibial tuberosity to the medial side of the knee. The zone is located distally from 50% of the vertical line and medially from 66% of the horizontal line. MOI—the incision midpoint was median point of the bottom edge of the triangle, through this midpoint and the oblique angle with the bottom edge was 51° and extended posteriorly and anteriorly