Purpose: No conventional surgical technique for ligament reconstruction can be used in all cases to achieve ideal position of the transplant. Navigation systems without visualisation of the anterior cruciate ligament should meet the requirements. This is an operative strategy based on one or more computer assisted procedures enabling ligament reconstruction without the need for conventional pre- per, or postoperative imaging. The principle is based at the present time on the use of a station (computer, localisers, display screen, command pedal) used for processing data (spatial measurements and positioning) delivered by markers fixed on rigid bodies and tools (palpation, aiming tools).

Material and methods: This study was conducted on ten cadaver knees. Each knee was instrumented with the station. Joint kinetics were recorded with and without the ACL and after harvesting the transplant: patellar ligament and hamstring ligaments. Bone morphing was used to draw the tibial and femoral surfaces. Two types of aiming tools were tested by recording the data points issuing from the tibial output and the femoral input. The position of the femoral and tibial holes was determined to achieve the smallest anisometry and absence of notch conflict. Isometric zones were compared with the anatomic zones of the ACL. We also compared the position of the transplant determined by the computer and that determined according to the methods of conventional arthroscopy. An x-ray of each knee was obtained to compare with data in the literature concerning the advised position of the femoral and tibial holes with that established by the computer navigation system. Each knee was tested with KT1000 before and after surgery.

Results: The precision of bone morphing was 0.1 mm. Anisometric curves were compatible with drilling holes calibrated to the size of the implant in four knees. The operator used the navigation system to determine the point of the femoral hole in six knees. The system then calculated the point of the tibial hole automatically eliminating the risk of notch conflict. The anisometric values were less than 2 mm; the distance roof of the notch/anterior border of the transplant was calculated as a function of the radius of the transplant (3.5–5 mm). The position of the tibial hole given by the computer system was always more medial than that given by the tibial aiming tools. The position of the femoral tunnel was always more anterior than that given by the femoral aiming tools. The postoperative KT1000 values were identical to the preoperative values.

Discussion: Navigation without visualisation of the ACL is able to position the ACL in an isometric plane or better in an “anatomometric” plane, to inscribe the joint orifice of the tibial hole on the projection of the anterior arch of the notch on the tibial surface, to draw in real time the isometric femoral map on the notch in order to centre the joint orifice of the tibial hole as well as the corresponding laxity map, to indicate on the femoral notch the point which will be the centre of the joint orifice of the femoral hole, to draw the isometric curve of a given fibre and its corresponding laxity map, and to detect and allow the treatment of any transplant-notch conflict.