Navigation of Uni knee arthroplasty (UKA) is not common. Usually the software includes navigation of the tibial as well as the femoral implant. In order to simplify the surgical procedure we thought that navigation of the tibial plateau alone could be a good option. Since 2005 we have been using a mobile bearing UKA of which the ancillary is based on dependent bone cuts. The tibial cut is made first and the femoral cut is automatically performed using cutting blocks inserted between the tibial cut and the distal end of the femur. Although we are satisfied with this procedure, it is not rare we have some difficulties getting the right under correction needed to get a good long-term result. The aim of this paper was to present our computer-assisted UKA technique and our preliminary radiological results in genu varum (17 cases) as well as genu valgum (6 cases) deformities.

The series was composed of 23 patients, 10 females and 13 males, aged from 63 to 88 years old (mean age: 75 +/− 8). The mean preoperative HKA (Hip-Knee-Ankle) angle was: 172.35° +/− 2.31° (167° to 176°) for the genu vara and 186.33° +/− 2.87° (182° to 189°) for the genu valga.

The goal of the navigation was to get an HKA angle of 177° +/− 2° for genu varum deformity and 183° +/− 2° for genu valgum.

We used the SURGETICS® device (PRAXIM, GRENOBLE, FRANCE) in the first six cases and the ORTHOPILOT® device (B-BRAUN-AESCULAP, TUTTLINGEN, GERMANY) in the other cases. The principles are the same for both devices. The 1rst step consists in inserting percutaneously the rigid-bodies on the distal end of the femur and on the proximal end of the tibia. Then, we locate the center of the hip by a movement of circumduction, the center of the ankle by palpating the malleoli and the center of the knee by palpating intra articular anatomic landmarks to get the HKA angle in real time. This step is probably the most important because it allows checking the reducibility of the deformity in order to avoid an over correction when inserting a mobile bearing prosthesis. The 3^rd step consists in navigation of the tibial cut such as the height of the resection, the tibial slope (3 to 5° posterior tibial slope) and the varus of the implant (2 to 3°). Once the tibial cut was done, we must use the conventional ancillary to perform the femoral bone cuts (distal and chamfer). The last step consists in inserting the trial implants and checking the HKA angle and the laxity of the medial or lateral side.

We used postoperative long leg X-Rays to evaluate the accuracy of navigation and plain radiographs to evaluate the right position of the implant.

As far as genu varum deformity was concerned, the mean postoperative HKA angle was 177.23° +/− 1.64° (173°–179°). The preoperative goal was reached in 94% of the cases. Moreover, this angle could be superimposed on the peroperative computer-assisted angle, which was 177° +/− 1.43° (p>0.05). For genu valgum, the mean postoperative HKA angle was 181° +/− 1.41° (179°–183°). The preoperative goal was reached in 66% of the cases but the series is too short to give any conclusion.

The navigation of tibial plateau alone can be used with accuracy, provided one has the right ancillary to use dependent bone cuts. The procedure is quick and needs only one tibial cutting guide equipped with a rigid-body. Our results, especially in genu varum deformity, are quite remarkable. Regarding genu valgum, the results seem to be less accurate, but the software was designed for medial UKA and the series is short, so, it is too soon to extrapolate any conclusion. The main interest in this navigation is to avoid too much under correction and even better to avoid over correction when the deformity is over reducible. Indeed, when one uses a mobile bearing plateau, the risk is to have a dislocation of the meniscus. So, when tightening the collateral ligaments, checking the lower limb axis may persuade not to use a mobile bearing plateau but rather a fixed plateau.

Poor outcome in ACL reconstruction is often related to tunnel position. This study investigates the use of surgical navigation to improve outcome. Improving accuracy of tunnel position will lead to improved outcome.

In a prospective randomised controlled trial 60 ACL plasties with quadruple-loop semi-tendinosus and gracilis tendon were randomised to either standard instrumentation or computer assisted guides to position the tibial and femoral tunnels. The results were evaluated on clinical outcome based on IKDC laxity measurements and radiologic assessment of anterior drawer at 150 and 200N as well as radiological assessment of the tunnel positions.

No complications were observed in either group. IKDC laxity was level A in 22 knees in the conventional group (average 1.5 mm (0-6) at 200N) compared with 26 navigated knees (average laxity 1.3mm (0-5)). Laxity was less than 2 mm in 96.7% of the navigated group (83% in conventional group). The variability of laxity in the navigated group was significantly less than the conventional group, with the standard deviation of the navigated group being smaller than the conventional group standard deviation (p = 0.0003 at 150N and 0.0005 at 200N TELOS).

A significant difference (p=0.03) was found between the groups in the ATB value characterising the sagittal position of the tibial tunnel (negative ATB values imply graft impingement in extension). In the conventional group mean ATB was -1.2 (-5-+4) while it was 0.4 (0 - 3) in Group II. There were no negative ATB values in the Navigated Group.

The use of computer assisted navigation creates a more consistently accurate tibial tunnel position than using conventional techniques. It is suggested that this should reduce impingement and improve graft longevity.