Fracture-table-mounted versus bone-mounted dynamic reference frame tracking accuracy using computer-assisted orthopaedic surgery–a comparative study

Figures & data

Figure 1. Standard fluoroscopic-based navigation for cannulated screw insertion. The dynamic reference frame (labeled RF) is attached to the iliac crest. A tracked drill guide (DG) is used for planning the screw's trajectory, and a guide wire is than inserted through it. The computer display (CD) displays the virtual image of the drill guide trajectory (green line) on both the AP and lateral views simultaneously. [Color version available online.]

Figure 2. The validation phase. New images are taken after the insertion of the guide wires. The drill guide is placed over the wires and the navigated virtual image (green line) is superimposed on the “real” radiographic image (black line). The discrepancy between these images in both translation and angulation is calculated. [Color version available online.]

Figure 3. Table-mounted (A) and iliac-crest–mounted (B) dynamic reference frame attachments. The drill guide (C) is also visible.

Figure 4. Determination of the trajectory translation at the entry point (d_entry) and tip (d_tip), and of the angle between the trajectory image and the k-wire fluoroscopic images (alpha).

Table I.  Translational offset (in mm) of the trajectory from the drill guide at the two sites (d_tip and d_entry) in the AP view.

	Anteroposterior view
	Difference		Fracture table		Iliac crest
	d_tip	d_entry	d_tip	d_entry	d_tip	d_entry
Average	1.75	0.91	1.85	1.24	1.25	1.18
Min	0.03	0.00	0.00	0.00	0.00	0.00
Max	4.81	2.55	5.17	2.93	6.87	3.91
SD	1.41	0.70	1.37	0.90	1.53	0.92
p value	NS	NS

Table II.  Translational offset (in mm) of the trajectory from the drill guide at the two sites (d_tip and d_entry) in the lateral view.

	Lateral view
	Difference		Fracture table		Iliac crest
	d_tip	d_entry	d_tip	d_entry	d_tip	d_entry
Average	1.20	1.00	1.57	1.26	1.63	1.42
Min	0.18	0.05	0.07	0.00	0.00	0.00
Max	2.86	2.11	3.03	2.62	4.87	3.02
SD	0.73	0.62	0.85	0.71	1.25	0.88
p value	NS	NS

Table III.  Angular offset (in degrees) in the AP and lateral views.

	AP view		Lateral view
	Fracture table	Iliac crest	Fracture table	Iliac crest
Average	1.07	0.88	1.20	1.05
Min	0.00	0.00	0.00	0.00
Max	2.99	3.45	3.07	2.92
SD	0.82	0.82	0.80	0.84
p value	NS	NS	NS	NS