Introduction: Restoration of neutral alignment of the leg is an important factor affecting the long-term results of total knee arthroplasty (TKA). Recent developments in computer-assisted surgery have focused on systems for improving TKA. To verify that computer assistance improves the leg alignment and the component orientation, we present a single center study with 1000 patients.

Materials and Methods: In a prospective study two groups of 500 patients each undergoing TKA had operations using either a computer-assisted image free navigation system or a conventional technique. Alignment of the leg and the orientation of components were determined on post-operative long-leg coronal and lateral films.

Results: The mechanical axis of the leg was significantly better in the computer-assisted group (97%, within ±3° varus/valgus) compared with the conventional group (78,5%, within ±3° varus/valgus). The coronal alignment of the femoral component was also more accurate in the computer-assisted group.

Discussion: Computer-assisted TKA gives a better correction of alignment of the leg and orientation of the components compared with the conventional technique. Potential benefits in the long-term outcome and functional improvement require further investigation.