Fabio Cantani, MD, et al.
The Journal of Bone and Joint Surgery. April 2008. Vol. 90-A. No. 4. Pp. 764-771.

Computer-navigated total knee arthroplasties (TKA) are improving the accuracy of the implantations and studies are finding that navigation-assisted surgery is providing better outcomes in terms of alignment of the femoral and tibial components. However, because the navigation is performed before the actual manipulations, optimal positioning is not always obtained.

Errors causing misalignments can result from any of the many steps in the surgical process, from the accuracy of the navigation system to the application and manipulation of the cemented or cementless components. Up to now, previous studies have investigated the accuracy of the navigational systems and have found great differences between the results.

Of particular importance, but one that is not given a lot of notice, is the final positioning of the femoral and tibial components. While the navigational systems check the alignments throughout the process, checking after the final positioning is rarely done.

The authors of this study wanted to see how measuring the positioning after final alignment would affect the outcome. Researchers enrolled 91 patients who were to receive a primary TKA because of osteoarthritis. Patients who were having revision surgery, or who had infections or knee instability were not candidates for this study. At the beginning of the surgery, the surgeons attached navigation trackers to measure placement. The positioning was measured at set times throughout the procedure and, unlike other studies, again after the components were in place and the cement had hardened.

The results showed that there were deviations in the angles ranging anywhere from zero to three degrees, regardless of how carefully the surgery was performed and how accurately all the steps were completed. Therefore, even careful measurement throughout surgery, does not always result in optimal results.