Experience of total knee arthroplasty using a novel navigation system within the surgical field

With the aim of improving component alignment and outcome in total knee arthroplasty (TKA), several computer-assisted devices (CAD) have been developed.

In February 2014, the present unit started to use a new imageless navigation system with accelerometric pods within the surgical field for all primary TKAs; there was no need for optical trackers or cameras. This paper presents the results of the first 72 TKAs using this iAssist system in 71 prospectively collected and retrospectively analyzed patients. It analyzed component positioning in standard and full-length leg x-rays.

The mean age of the patients was 70 years (range 52–88). The center of hip, knee and ankle (mechanical axes) deviated on average 0.5° (standard deviation (SD) of 1.8) valgus from the targeted straight alignment. Three TKAs had >3° deviation (i.e. four degree varus, five degree and seven degree valgus). The frontal tibial tray alignment was an average of 89.9° (range 86.4–100.1°, SD ±2.0) with the target being 90°, and the sagittal slope was as targeted at 85.0° (range 78.4–88.8°, SD ±1.7).

This CAD facilitated good mechanical alignment and reproducible accuracy in component positioning. Pods clipped onto cutting jigs within the surgical field provided simple and accurate navigation, with little extra time needed for calibration and no need for optical trackers or pre-operative imaging.