The distal end part of the retractor according to the invention is provided both with terminal tips for abutment on one of the femoral condylar walls which define therebetween the intercondylar space, and with a wing extending laterally in projection from this end part in order to form a frontal surface for thrust, in a medial-lateral direction, of that part of the quadriceps muscle tendon containing the patella when the tips are in abutment in the intercondylar space. By using this retractor as a lever, the wing efficiently reclines the patella, without turning it completely on itself, entirely exposing one of the femoral condyles. This invention is more particularly applicable to a surgical procedure for implanting a unicompartmental knee prosthesis.