FIELD : medicine.SUBSTANCE : prosthetic knee joint comprises an upper part, a lower part, a fastening device for a proximal prosthetic element, a fastening device for a distal prosthetic element and a four-limbed joint system. Lower part is rotatable relative to the upper part. Fastening device for the proximal prosthetic element is mounted on the upper part. Fastening device for the distal prosthetic element is installed in the lower part. Four-limbed joint system comprises four linkages articulatedly fastened to each other, which are pivotable to each other around a pivot axis. Upper part is mounted on a joint system. Joint system rests on the lower part is configured to rotate from an initial position against the force of elasticity during bending in the supporting phase, wherein the position of the articulation links relative to each other remains unchanged, and the line of action of the force of elasticity is directed so that there is a moment opposing the bending inside the joint system.EFFECT : invention provides the possibility of bending inside the prosthetic knee joint during bending in the supporting phase.10 cl, 2 dwg