Preliminary radiological evaluation of the Vector Vision CT-free knee module for implantation of the LCS knee prosthesis.

We have assessed the bone cuts achieved at surgery as compared to the planned cuts produced during computer assisted surgery (CAS) using a CT-free navigation system. In addition, two groups of matched patients were compared to assess the post-operative mechanical alignment achieved. Fourteen patients received a LCS total knee replacement (TKR) using the Vector Vision module and 14 received a TKR using a conventional method of extramedullary alignment jigs. The deviation in each plane (valgus-varus, flexion-extension and proximal-distal) was calculated. For the tibia the mean deviation in coronal plane was 0.21 degrees of varus (SD=1.37) and in the sagittal plane was 1.29 degrees of flexion (SD=3.73) and 0.24 mm of resection distal to the anticipated cut (SD=2.14). For the femur the mean deviation in the coronal plane was 0.88 degrees (SD=2.2) of valgus and in the sagittal plane the mean deviation was 0.3 degrees (SD=2.91) of extension. In the transverse plane there was a mean deviation of 0.07 degrees (SD=1.57) of external rotation. There was a mean deviation of 2.33 mm of proximal resection (SD=2.9) and 1.05 mm of anterior shift (SD=2.81). On comparing the two groups, no statistically significant differences were found for the angles between the femoral component and the femoral mechanical axis, the tibial component and the tibial mechanical axis, the femoral and tibial mechanical axis and the femoral and tibial anatomical axis. This study has presented preliminary data regarding the efficacy of a particular navigation system with regards to improving upon the accuracy of component position with the long-term aspiration of improving upon TKR longevity. A further randomised controlled trial with greater numbers of cases and controls would improve upon our knowledge as to the efficacy of the Vector Vision system and a power analysis based upon the findings of this pilot study has suggested that at least thirty subjects be included in each group.