EFFECT OF CEMENTING ON ALIGNMENT IN COMPUTER NAVIGATED TOTAL KNEE REPLACEMENT

Abstract

Computer Navigation systems are becoming more widely used for knee replacement surgery. We used the Stryker Navigation System® to assess the alignment of twenty-two knees intraoperatively. We compared alignment readings of valgus angle of the knee in extension before and after cementing of the prosthesis.

We found that in twenty of the twenty-two cases (91%), a change in alignment occurred between bone cuts stage, and final cemented prosthesis. The mean change between trial alignment and final cemented alignment was 1.5 degrees (0.5 to 4.5 degrees). Twelve cases showed an improvement in alignment on cementing (ie. tended towards zero degrees) with a mean of 1.4 degrees (0.5 to 3.5). Eight cases showed a deterioration in alignment (ie. tended further away from zero degrees) with a mean of 1.1 degrees (0.5 to 2.5). Two cases showed change in alignment without being considered worse or better ie. changed from varus to valgus or vice versa to the same degree.

We conclude that in order to benefit maximally from the accuracy of the computer navigation system, care must be taken to ensure accurate seating of the prosthesis following cementing. The changes we observed in some cases between trial alignment and final cemented result, suggest that the high level of accuracy in alignment gained by the computer navigation system may be lost at the cementing stage. We therefore recommend that alignment is rechecked immediately following cementing, and valgus or varus force carefully applied as appropriate to achieve ideal alignment before cement polymerisation.