Soft tissue management is a critical factor in total knee arthroplasty especially in valgus knees. The stepwise release has been based upon surgeon’s experience until now. Computer assisted surgery gained increasing scientific interest in recent times and allows the intraoperative measurement of leg axis and gap size in extension and flexion. We therefore aimed to analyse the effect of the sequential lateral soft tissue release and the resulting change in the a.p. limb axis on the one hand and the tibiofemoral gaps on the other hand as well in extension as in flexion in 8 cadaveric knees. Measurements were obtained using a CT-free navigation system. In extension the highest increase compared to the previous release step was found for the first (iliotibial band, p=0.002), second (popliteus muscle, p=0.0003), third (LCL, 0.007) and the sixth (entire PCL, p=0.001) release step. In 90° flexion all differences of the lateral release steps were statistically significant (p<
0.004). Massive progression of the lateral gap in flexion was found after the second (popliteus muscle, p=0.004) and third (LCL, 0.007) release step. Computer assisted surgery allows to measure the effect of each release step of the sequential lateral release sequence and helps the surgeon to asses the result better.
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.