Abstract 6

Accuracy of a computer-assisted navigation system for total knee replacement

I.A. Anderson¹, A.J. Graydon², S.F.F. Malak1, R.P. Pitto²

¹ Bioengineering Institute, University of Auckland, New Zealand

² Middlemore Hospital, Department of Orthopaedic Surgery, University of Auckland, New Zealand

The purpose of our study was to assess the accuracy of an image-free TKR navigation system: 1) in a leg with a normal mechanical axis and, 2) in a leg with an abnormal mechanical axis.

We evaluated the Ci-CAS TKR navigation system of BrainLab and DePuy International. An artificial leg (phantom) was constructed to simulate hip and knee joints. The juxta-articular knee surfaces were composed of a synthetic material (Sawbones - Pacific Laboratories). A highly accurate digital calliper unit (FaroARM Technologies, USA) was used to measure co-ordinates of pre-machined points on the phantom, A software program was developed to calculate actual leg alignment angles. This technique was verified using repeated measurement with variable co-ordinates, giving accuracy to within 0.05 of a degree.

Simulated procedures were then performed with both a normal and abnormal leg mechanical axis. At specific points in the procedure, information was compared between the FaroARM digital measurements and the Ci-CAS system. Repeated serial measurements were undertaken. In the setting of normal alignment, accuracy to within 0.5 degrees was demonstrated. In the setting of abnormal x,y and z plane alignment in both femur and tibia, accuracy to within 0.5 degrees was demonstrated.

This is the first study to assess the accuracy of a clinically validated navigation system. The study demonstrates the high level of in-vitro accuracy of the Ci navigation system in both normal and abnormal mechanical leg alignment settings.

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