The present invention relates to a percutaneous patellar osteosynthesis system applicable to any type of fracture of the knee cap, formed by two arms that contain two multidirectional movable securing devices for fitting to any type of knee cap, in which the arms close in a parallel manner by means of a scissors closure mechanism in order to keep the fragments confined and secured by means of a “zipper” based on manual compression. The devices for securing the knee cap have antero-posterior, up/down and also lateral mobility in order to mobilize the fractured fragments and to achieve a reduction and a satisfactory knee cap joint congruence. The arms have slidable guides for placing the implant in any required direction in order to keep the fragments stable, the guides slide on the arms and the parallelism sought in this type of fixing is achieved without having to be based on manual calculation, the latter customarily being used in broad tissue dissection. The system achieves reduction and internal fixing by means of a minimally invasive technique and less tissue damage. The system also has guides for fitting cerclage wiring on an implant of any configuration, facilitating reduction and fixing of patellar fractures and the taking of X-rays with the system in place.