Introduction: Minimal-invasive techniques in total joint replacement are perceived to reduce soft tissue trauma. In TKR, reduced exposure during surgery bares the risk of component malpositioning. Therefore we have combined minimal invasive surgical techniques with non-CT based navigation in TKR. The purpose of this observational study is to describe first results of a controlled observational study comparing minimal invasive navigated total knee arthroplasty (MINI-NAV-TKR) to open navigated total knee arthroplasty (NAV-TKR) with respect to component positioning, surgery time and immediate postoperative complications.

Materials and Methods: From June to September 2004, 26 MINI-NAV-TKR and 33 NAV-TKR have been performed by five surgeons in an unselected group of patients. In both groups, preoperative deformation of the mechanical leg axis was compared to postoperative mechanical leg axis using total one-leg standing radiographs. To control the safety and reproducibility of both procedures, time of surgery and postoperative complications were compared among both groups.

Results: Given informed consent, 17 females and 9 males received 26 MINI-NAV-TKR, mean age was 71,06 years (ranging from 56,24 years to 84, 35 years), mean BMI was 28,8 kg/m2 and preoperative mechanical leg axis ranged from 18o varus to 16 o valgus. In NAV-TKR group, 12 males and 21 females at a mean age of 68,75 (range 51,97 to 86,73 years) received 33 TKR, mean BMI was 30,6 kg/m2 and preoperative mechanical axis ranged from 11 varus to 20 valgus. Postoperative radiographic leg alignment in the MINI-NAV-TKR group ranged from 1 degree valgus to 3 degree varus mechanical axis as compared to the NAV-TKR that ranged from 1 valgus to one outlayer of 4 degree varus. Time of surgery significantly differed among the groups (mean time Mini-NAV-TKR 115,23 min versus mean time NAV-TKR 98,15 minutes, p=0,002). In the MINI-NAV-TKR group 1 postoperative pin-infection and one conversion to an open procedure have been reported, in the NAV-TKR group 2 hematomas have been described.

Conclusion: Despite increased mean time of surgery in the MINI-NAV-TKR group, component positioning and complications are comparable between both groups. These preliminary results indicate, that MINI-NAV-TKR combined with navigation is a safe and reproducible method.