This surgical apparatus comprises, on the one hand, means for spatial
marking-out of the kneecap and femur of a patient to be operated on, and,
on the other hand, means for simultaneous and relative representation of
this kneecap provided virtually with a patellar implant of the
prosthesis, and of this femur provided virtually with a femoral implant
of the prosthesis, in a sagittal plane passing both through the kneecap
and through the trochlea of the aforementioned femoral implant. Using
this apparatus, the surgeon can easily and quickly check the
antero-posterior size of the prosthesis in order to reduce the risks of
subsequent dislocations of the kneecap fitted with the prosthesis.