Aims: Kinematic and pointing procedures, are used for non-image based navigated implantation of TKA. Pointing procedures require exact knowledge about the landmarks. In this anatomical study, landmarks are defined and repeatedly referenced. The precision and the reproducibility are evaluated, by means of inter- and intra- observer study. Using the landmarks, the axes of the femur and tibia are calculated. Methods: The specific landmarks of 30 femur and 27 tibia specimens, were palpated by 3 surgeons and digitised by means of a photogrammetric system, as used intra-operatively. The recorded data are evaluated. Results: The specific landmarks can be referenced with great precision. The vectors that influence the implant position, show femoral a mean inter-observer deviation of 0,9mm and 1,0mm tibial. The repeating accuracy of every single observer was 1,5mm femoral and 1,0mm tibial. The calculated long axes at the femur and tibia, thus reach a precision of 0.1° (min-max:0°–0,9°) at the femur and 0,2° (min-max:0°–1,1°) at the tibia. The short axes at the distal femur and at the proximal tibia, exhibit an average deviation of 0,7° to 1,9° (min-max: 0°–11,3°). Conclusion: Long axes (mechanical axes) can be determined exactly, the precision of the short axes (rotational axes) is unsatisfactory, although palpation of landmarks were accurate. Therefore, palpation of more than one rotational axis at the femur and the tibia, is mandatory and should be visualized on the monitor during the operation.

Aims: The mini-robot-supported ligament balancing technique of the Galileo navigation system is described “step by step”. Methods: The aim of an optimal ligament balancing is a symmetrical ligament tension as well as flexion and extension gaps which are equal and right-angled. This is reached with the Galileo system through: 1) Robot controlled shifting of the resection block in anterior-posterior and/or proximal-distal direction. 2) Use of an instrumented ligament spreader which measures force and joint gap. The flexion gap measurement is conveyed to the computer which calculates the optimal proximal-distal position of the implant. Then the robot-controlled resection block is positioned accordingly. Results: Surgical Technique: The tibial and the posterior femoral resections are carried out first. The spreader is then inserted into the flexion gap with a ligament tension of 100N for both, medial and lateral condyle. The polyethylene thickness is chosen assuming a right-angled configuration (same gap medial and lateral) and reported to the computer. Then the spreader is inserted into the extension gap, aligned to the axis and a ligament tension of 100 Newton is applied. Should the extension gap not be right-angled, corresponding soft tissue releases have to be performed. The medial and lateral extension gap is entered into the computer which calculates the optimal implant position and positions the robotcontrolled resection block. The resection is performed with a conventional bone saw. Conclusions: Galileo is a practice oriented navigation system for TKR with integrated mini-robot. The resection block positioning in 0,5 mm steps in anterior-posterior and proximal-distal direction enables optimal ligament balancing. The combination of ligament spreader and navigation results in perfect ligament balancing and reconstruction of the mechanical axis even with large axis deviations and pathological ligament deformations.