Background: During the past decade, there has been a resurgence of interest in hip resurfacing as a mode of treatment for the younger patient with hip disease since major disadvantages of previous resurfacing systems have been overcome. The purpose of the presented study was to clarify if an imageless navigation system will allow precise placement of the femoral component.

Methods: Between September 2004 and May 2006, 50 metal-on-metal surface arthroplasties each were performed either using an imageless navigation system or the conventional technique. The inclination and the axial alignment of the femoral component were determined by two independend examiners and compared to the values presented by the navigation system.

Results: In the preoperative x-rays a mean CCD-Angle of 129.2 degrees (Control group: 127.5°) was measured. The mean femoral shaft angle was 137.5 degrees (Control group 133°) postoperatively with a mean deviation of 2.1 degrees compared to the values shown by the system. In the computer assisted group the mean deviation from the ideal placement in the axial plane was 2.9 degrees compared to 4.8° when using the conventional technique.

Conclusion: The use of a navigation system was associated with only an average time loss of 7 minutes for surface data acquisition und mounting of the reference base. The computer assisted technique appears to be helpful to avoid notching during the femoral bone preparation and improve implant positioning which might improve durability.

Introduction: Previous reports have described the potentially compromising effect of a high tibial osteotomy (HTO) on the results of a subsequent total knee arthroplasty (TKA). Although the reasons are not clear, some authors reported of problems in soft tissue balancing in TKA following a previous HTO.

Method: In a prospective study 22 patients with an average interval of 5.8 years after closed wedge HTO, were operated for TKA. All surgeries were performed with the BrainLAB CT-free navigation system and measurements of the extension and flexion gap were assessed. The intraoperative data were compared to a control group of 100 consecutive computer assisted TKA without previous HTO.

Results: In the study group a highly significant shift towards a medial opening of the flexion gap between the posterior condylar line and the tibial resection (study group 0.4° +/− 4.7° medial opening vs. control group 3.4° +/− 3.3° lateral opening, p< 0.001) was observed. 45% in the study group showed a medial opening of the flexion gap compared to 11% in the control group.

Conclusion: Surgeons should be aware of difficulties in soft-tissue balance in TKA following HTO, especially for the flexion gap configuration and the axial femoral component orientation. The computer assisted technique is helpful to identify soft tissue imbalance.

The accuracy of component implantation is an important factor affecting long term results of unicompartmental knee replacement (UKR), particularly, since overcorrection of the leg axis has been associated with an inferior patients outcome. This problem is aggravated when using a minimally invasive approach with a limited view.

In a prospective study, two groups of 40 UKR each were operated either using a non-image-based navigation system or the conventional technique. Radiographic assessment of postoperative alignment was performed by postoperative long-leg coronal and lateral x-rays.

The results revealed a significant difference between the two groups in favour of navigation with regard to the mechanical axis, as well as the coronal femoral and tibial alignment. In the computer assisted group 38/40 (95%) of UKR were in a range of 4 Degree to 0 degree varus (mechanical axis) compared with 29/40 (72,5%) in the conventional group. There was no significant difference between the groups concerning postoperative range of motion, blood loss and pain score.

The only inconvenience was a lengthening of the operation time (20 min). Due to the limited exposure in minimal invasive unicompartmental TKA the navigation system is helpful in achieving a more precise component orientation. The danger of overcorrection is diminished by real time information about the leg axis at each step during the operation. This improvement could be related to a longer survival rate.

Introduction Correct postoperative leg alignment and stability of total knee prothesis over the full range of movement is one critical factor for successful TKA. This can only be achieved by correct implantation of prothesis and soft tissue handling. Still arthrotomy, surgical approach and handling of patella are discussed controversially.

Materials and Methods In a cadaver specimen study we evaluated the influence of everted or subluxated patella on limb axis during balancing of the knee in three different standard surgical approaches. For each approach we operated five knees. Leg alignment was visualised by Ci CT-free DePuy/BrainLAB navigation system. First, physiological leg alignment was measured. Then the different approaches were performed and a.p. leg axis was first measured and compared as well with everted as with subluxed patella in extension and second in 90 degrees flexion.

Results Eversion of patella leads to an alteration in leg axis compared to subluxed patella of 0.58 degrees (SD: 0.03, range: 0.54–0.6) limb axis in valgus direction in full extension. In 90 degrees flexion we found a mean deviation of leg axis of 0.48 degrees (SD: 0.11, range: 0.38–0.6) with everted patella compared to subluxed patella.

Discussion The surgeon has to be aware of this falsifying influence of everted patella to the a.p. limb axis.