Pelvic tracker effects on hip center accuracy using imageless navigation

Figures & data

Figure 1. Scatter plots showing the resultant scalar distances from the true hip joint center with (a) and without (b) a pelvic tracker. Note the tighter grouping of data points and fewer outliers in the pelvic tracker plot (all axes are marked in mm).

Table 1.  Errors in the x-, y-, and z-directions associated with pin-based and pinless computer assisted HJC localization. δ is the scalar distance from the calculated HJC to the true center as determined by CT.

	Pin-based	Pinless
x
Mean	− 0.81	− 1.08
SD	2.23	2.64
Max	6.46	3.72
y
Mean	− 0.11	− 2.37
SD	1.04	2.55
Max	3.87	2.84
z
Mean	0.73	2.62
SD	2.76	7.40
Max	5.54	32.53
δ
Mean	3.31	7.52
SD	1.95	5.00
Max	12.55	32.72

Figure 2. Sagittal and coronal malalignment of the mechanical axis following pelvic tracker-based and tracker-less functional algorithms (+sagittal angle = flexion; + coronal angle = varus in degrees; *p < 0.05 when comparing algorithms with and without a pelvic tracker).