ELECTROMAGNETIC COMPUTER ASSISTED NAVIGATION OF TOTAL KNEE JOINT REPLACEMENT VERSUS THE CONVENTIONAL TECHNIQUE – THE EARLY EXPERIENCE IN A PROVINCIAL HOSPITAL IN NEW ZEALAND

Abstract

Background: Computer Assisted Orthopaedic Surgery continues to evolve. Electromagnetic Computer Navigation has recently emerged as a new modality of CAOS that promises increased accuracy, as well as increased portability and practicality. However, there are very few studies examining this new technique and comparing it to conventional TKJR.

Methods: We carried out a prospective randomised study comparing the conventional jig-based technique of TKJR versus EM navigation (Medtronic). We examined parameters such as surgical time, blood loss, days in hospital post operatively, and complication rate. Further, we assessed the accuracy of the two techniques with the CT Scan “Perth Protocol”. Parameters measured included femoral component flexion, extension, alignment and rotation, tibial alignment, posterior slope and femorotibial mismatch.

Results: Mean Oxford Knee Score was 47.5; the mean age was 70 (67–74). 43% were female and 57% male. Half were navigated and half conventional. The mean Hb change in 48 hours, as a reflection of blood loss was 14.5% for the conventional group and 14.25% for the navigated group. Mean Surgical Time for the conventional group was 90 minutes and the navigated was 120 minutes. The average stay in hospital for both groups was 5 days after the operation. The measurements according to the Perth Protocol suggested increased accuracy in femoral alignment, posterior slope, and reduced femorotibial mismatch. Femoral rotation was not significantly different and femoral flexion extension was not significantly different. The only major complication occurred in the navigated group with a dislocated knee in a patient afflicted with multiple sclerosis.

Summary: These preliminary results suggest that EM navigation is a safe and accurate technique. It has the additional advantage of portability and increased user friendliness compared to other navigation methods. When compared to conventional jig-based techniques, it is more accurate, increases surgical time by an average 30 minutes, there is no significant difference in blood loss at 48 hours, patient’s stay in hospital is not prolonged and the rate of complications does not exceed that of conventional surgery.

Electromagnetic Navigation is in its infancy, and the authors feel that surgical time and accuracy will improve with more frequent use and the development of increasingly more sophisticated software packages. Our study continues.