1. Field of the Invention
This invention concerns a surgical ancillary instrument allowing the marking of the entrance hole to the femoral insertion tunnel of a neo ligament for the reconstruction of the anterior cruciate of the knee, in the total respect of its isometry, as well as the guiding of an instrument for the drilling of the same tunnel and beneficially allowing the guiding of an instrument for the drilling of a tibial insertion tunnel of the same neo-ligament.
2. Discussion of Background and Relevant Information
The main problem encountered reconstructing the anterior cruciate of the knee is with respect to its isometry. By isometry, is meant the fact that the distance between the point of insertion of the ligament in the tibia and the point of insertion of the same ligament in the femur should not vary no matter what the degree of flexion or extension of the knee. Indeed, it can be imagined that if this isometry were not respected, there would be a lack of stability in the positions where the ligament is relaxed and, on the contrary, a limitation of mobility if, in a certain position the ligament were submitted to an excessive tension.
Generally speaking, the tibial insertion of the ligament is easily found considering its very anterior position on the tibial plateau. It is not the same for the femoral insertion which is carried out on the axial side of the external femoral condyle within a deep seated area, difficult to see directly by the surgeon. This femoral insertion area also greatly varies from one person to another and the choice of this point is usually left for the surgeon to appreciate. Moreover, it is important to plan when implanting a prosthetic ligament of knee, a the perfect alignment of the longitudinal axes of the tibial and femoral insertion tunnels so that, the knee being in its extension position, the prosthetic ligament is straight so as to avoid all the useless efforts due to raised edges of the insertion tunnels.
The main object of this invention is therefore to offer the realization of a surgical instrument for marking with precision, in accordance to criteria capable of being measured and reproduced, the position of the hole at the entrance to the femoral insertion tunnel at the external condyle level.
In this respect, a number of drilling guides are known, but these guides allow insertion tunnels to be chosen between two points chosen at will depending on the surgeons experience. None of these guides at present allow to determine with precision the isometrical point which however is the compulsory point of entry to the neo-ligament, if a perfect isometry is required. Anatomical works, carried out amongst others by inventors, have enabled to establish with certainty that the far posterior part of the external femoral condyle actually corresponds to the quadrant of a perfect circle, the radius of which varies, depending on the person concerned. These same works have also enabled to determine that the geometrical center of this circle corresponded exactly to the sought isometric point. The location of this isometric point can therefore be determined in relation to its distance to the far edge of the condyle, insofar as it can be measured.
As of then, it is just necessary, prior to the operation, to practically determine the center of the circle mentioned above; namely by measuring its distance in relation to the rear edge of the condyle. It is well known how to take such a measurement from an X-ray without an enlargment by using teleradiography, for example. It would then be sufficient to superimpose transparent tracings to measure directly the radius of the circle corresponding to the posterior part of the femoral condyle and to deduce its center. From this same center it is easy to draw a line parallel to the bottom of the intercondyloid notch by marking, for example, the Blumensatt line, which is a well known radiological reference. This line corresponds exactly to the ideal axis of the femoral insertion tunnel in the reconstruction of the anterior cruciate of the knee. Finally, it is sufficient to note the distance thus measured on an appropriate instrument equipped with a display, taking reference on the posterior edge of the external condyle to obtain, with excellent precision, the isometric point of femoral insertion of the neo-ligament during the operation.