[Precision of guidewire placement--can it be improved by applying the new, isocentric aiming principle?]

Exact placement of a guidewire is difficult for the less experienced surgeon as this complex 3D task usually is controlled by means of 2D fluoroscopic projections. The new isocentric aiming principle presented here splits up the 3D task into two planar, 2D steps. Movements of the guidewire to achieve correct placement are limited to one plane per step and can therefore be exactly controlled by fluoroscopy. The fluoroscopic projection needs to be changed only once in between the two steps.

The isocentric aiming principle became applicable to the proximal femur region by means of a mechanical aiming device. We have done an experimental study in order to compare the new isocentric aiming principle to the freehand aiming technique which is routinely applied. We documented the precision of guidewire placement achieved (angular deviation of the guidewire in two projections, linear deviation of the actual from the intended entry point), number of fluoroscopic controls, and procedure time when guidewire placement is done by an experienced and by an inexperienced surgeon.

When applying the isocentric aiming principle the inexperienced surgeon succeeded in fixing the entry angle of the guidewire more precisely both in the AP [1.3 degrees (0.0-2.0 degrees ) versus 2.3 degrees (0.0-9.0 degrees ), p=0.034] as well as in the axial view [1.0 degrees (0.0-2.5 degrees ) versus 6.5 degrees (0.0-12.0 degrees ), p=0.036]. Linear displacement was not significantly different between the two methods: 4.4 (0.7-9.6) mm deviation with the isocentric aiming principle versus 3.9 (1.6-5.7) mm, p=0.406, when the freehand technique is applied. When applying the isocentric aiming principle for guidewire placement the experienced surgeon achieved less precise angulation in the AP view [2.5 degrees (0.0-4.0 degrees ) versus 1.8 degrees (0.0-3.5 degrees ), p=0.061], improved precision in the axial view [2.0 degrees (1.0-3.0 degrees ) versus 3.0 degrees (0.0-5.0 degrees ), p=0.074], and a slightly worsened linear displacement [2.5 (1.0-4.2) mm versus 2.0 (1.0-2.6) mm, p=0.131]. Both surgeons needed less fluoroscopic controls when using the isocentric aiming principle instead of the freehand aiming method: inexperienced surgeon: 8.0 controls (7.0-16.0) instead of 13.0 controls (7.0-16.0), p=0.043; experienced surgeon: 14.5 controls (8.0-26.0) instead of 16.5 controls (12.0-33.0), p=0.282. However due to the additional time needed to fix and align the aiming device to the bone both surgeons required increased procedure time when using the isocentric aiming principle: 4.3 (3.0-6.9) min instead of 2.6 (2.2-4.0) min, p=0.005, for the inexperienced surgeon and 3.3 (2.3-4.3) min instead of 1.9 (1.4-2.8) min, p=0.001, for the experienced surgeon.

Based on the experimental results we would suggest clinical application of the isocentric aiming principle especially for the less experienced surgeon. Increased precision would outweigh the drawback of a slightly prolonged procedure time. X-ray exposure may also be reduced when using the isocentric aiming principle for guidewire placement. However our results have to be verified by a clinical study beforehand. The isocentric aiming principle can also be applied in other situations that allow for two orthogonal projections for guidewire placement.