The efficiency of a computer-integrated instrumentation system in knee arthroplasty was evaluated and compared with a conventional instrumentation system.
The OrthoPilot System defines the individual axis of the leg by means of an intraoperative kinematic analysis. LED's mounted on rigid bodies and screwed to the pelvis, femur and tibia are localized by a 3D infrared camera which is linked to a UNIX work station. The integrated calculation program leads to definition of the centres of hip, knee and ankle. Thereafter, LED-equipped alignment instruments allow definition of the femoral and tibial main resection planes.
The first sixty cases were included in the study. In addition, thirty cases each were entered into an OrthoPilot group and in a similar conventional control group. The navigated cohort consists of cases one to thirty, thus enclosing the "learning curve".
Leg axes and femoral and tibial angles were assessed radiographically at the three-months postoperative control. Radiological measurements of the OrthoPilot group were clearly superior to those of the manual group. The differences, however, were not statistically different in the parameters "mechanical axis", "femoral axis lat." and "tibial axis ap.". With regard to the parameter "tibial axis lat." a significant difference in favour of the navigation system was observed. The measurements of "femoral axis ap." were insignificantly better in the manual group. In general, a slight tendency towards valgus positioning of the femoral components when using the navigation system has to be discussed. Complications influencing the clinical outcome did not occur. Additional time for navigation is calculated in a range of ten to fifteen minutes.
The OrthoPilot system clearly facilitates proper alignment of endoprosthetic components in femur and tibia. Generally, the obtained values representing endoprosthetic alignment are superior to conventional technique. Marked deviations from ideal alignment can almost be avoided by means of the navigation system. During the learning curve the OrthoPilot system gained in reliability and reproducability.