Introduction: There is an ongoing discussion about potential risks and benefits of minimally invasive approaches (MIS) in total joint replacement. The aim of this study was to evaluate, whether a higher incidence of malalignments could be observed after minimally invasive navigated TKA and wether the results in the early postoperative period were better compared to standard approaches.

Methods: A total of 50 patients were treated with a navigated (OrthoPilot 4.2) Columbus knee prosthesis (BBraun Aesculap, Germany). In 25 patients either a standard or a minimally invasive (mini-mid-vastus) approach was carried out. In both groups the same exclusion criteria for MIS were adopted. Initially during surgery (Nav1a) and finally after implantation of the original components (Nav1b) the mechanical leg axis, passive range of motion and stability were measured by navigation according to the common workflow of the system. After restarting the software the same parameters were evaluated once more in a second procedure (Nav2) by reacquisition of joint centers both kinematically and by anatomical landmark palpation with the original prosthesis already implanted. Nav2 was conducted independantly from the initial surgical procedure. To validate the intraoperative measurements additional pre- and postoperative long-leg-standing radiographs were made. During the the first 10 days postoperatively daily range of motion (ROM) and pain (VAS) were measured. Perioperative blood loss and complications were documented. Results were analyzed by student’s t-test.

Results: Both groups were comparable with regard to preoperative demografic, radiologic and intraoperative data (Nav1a). There were no significant differences between the groups concerning intraoperative measurements of mechanical leg axis, passive range of motion and stability by Nav1b and Nav2. Additionally no differences were found for the alignment in the postoperative radiographs. The length of the skin incisions were significantly shorter in the minimally invasive group. Postoperative ROM was significantly higher and pain was significantly less intensive in the MIS group. Blood loss and complication rates were comparable.

Discussion: If the exclusion criteria for MIS were accepted no differences regarding the quality of alignment, passive range of motion and ligament stability could be demonstrated between conventional and MIS navigated TKA. Patients with MIS navigated TKA performed superior in terms of early p.o. function and pain. From the authors point of view the technically demanding minimally invasive implantation of knee prostheses should be exclusively performed with support of navigation.