Thirty-three knees in thirty-three patients who underwent ACLR using four-strand semitendinousus and gracilis tendon in our hospital were included in this study. In 17 knees, we use a fluoroscopic-based navigation system (Vector Vision ACL, BrainLab. Inc.) for positioning of the tunnels (Group 1). In the remaining 16 knees, positioning of the femoral and tibial tunnels was done without navigation (Group 2).

In navigation operation, anteroposterior and lateral images of the knee were taken with a fluoroscope and captured into the computer. The optimal target points for bone tunnels were semi-automatically calculated and displayed on the screen. Femoral placement was determined based on the quadrant method. The target for tibial tunnel was set at 43% of tibial plateau AP length. Intraoperatively, positions of the drill guides were decided referring to both navigation image and arthroscopic image. We evaluated Lysholm score, International Knee Documentation Committee (IKDC) subjective score, Lachman test and pivot shift test at 1 year after operation and calculated bone tunnel position on the postoperative lateral x-ray films and expressed them as relative values against total AP length of the Blumensaat's line and of the tibia plateau.

Lysholm score, IKDC subjective score, Lachman test and pivot shift test were not significantly differed between the groups. The femoral tunnels were 74.2±3.3% in Group 1 and 71.7±6.0% in Group 2 along and the tibial tunnels were 42.1±1.4% in group 1 and 43.0±4.6% in group 2 along the tibia plateau. Although femur and tibial tunnel positions were not significantly differed between the groups, variation of bone tunnel position was significantly smaller in Group 1, indicating a good reproducibility. One pin tract infection occurred in Group 1. This case successfully treated with debridment and antibiotics containing cement filling.

Fluoroscopic navigation system is quite helpful for precise and reproducible creation of both femur and tibial tunnel. The results encourage us to use this system for double-bundle anatomical ACLR. However, a special care must be taken to avoid complication caused by tracker pin placement.

The ligament balance as well as the alignment is essential for successful total knee arthroplasty (TKA). However it is usually assessed and adjusted only at 0? and 90?. In order to evaluate the ligament balance at the other angles we have used a navigation system. Twenty-one patients underwent posterior stabilised mobile bearing TKA using a CT-based navigation system were included in this study. Immediately post-operation and still under anaesthesia, varus and valgus stresses were applied on operated knees manually at 0?, 30?, 60?, 90? and 120?. The ligament balance was calculated based on the angles under varus and valgus stress displayed on the navigation screen, presenting a relationship between the femoral and tibial cutting planes. The mean ligament balance angle at 0?, 30?, 60?, 90? and 120? were −2? ± 3.6?, −5.8? ± 7.9?, 5.0? ± 6.9?, −1.3? ± 5.4?, 7.9? ± 7.2?, respectively. At 0? and 90? balance was well adjusted, however in the other angles, it was quite varied. At 30? and 120?, the lateral side was loose, on the other hand, medial side was looser at 60? knee flexion angle. The good balance at 0? and 90? is understandable because the balance is assessed and adjusted in these angles. Regarding the other angles, the 30? and 120? results corresponded with previous studies; however, the 60? results did not correlate. Although the reason is unknown, it must be aware the mid-flexion and deep flexion instability is quite common. Further investigations about the impact on clinical outcomes of such instabilities and how to adjust them if they are critical are needed.