The effect of adding tobramycin to Simplex P cement on femoral stem micromotion as measured by radiostereometric analysis

Figures & data

Figure 1. Participant flow.

Table 2. Precision of the RSA system in measurement of migration of the femoral stem centroid, based on 49 double examinations. The x-, y-, and z-axes correspond to the medial, proximal, and anterior axes, respectively

	Translation	Rotation
Axis	Mean absolute error	Mean absolute error
	(95% CI), mm	(95% CI), degrees
x	0.030 (+/- 0.092)	0.079 (+/- 0.200)
y	0.035 (+/- 0.087)	0.163 (+/- 0.501)
z	0.061 (+/- 0.157)	0.027 (+/- 0.079)

Figure 2. Mean subsidence of the stem centroid. Error bars represent the 95% confidence interval. Sample size (n) and p-values are shown for each group at each follow-up period.

Table 3. Two-year femoral component micromotion and differences for each cement group

	Simplex P		Simplex T		Difference	95% CI of the difference
Axis	Mean	SD	Mean	SD	(SimP–SimT)		p-value
Translation (mm)
xT: medial+ / lateral–	–0.01	0.09	0.01	0.13	–0.02	–0.11 to 0.08	0.8
yT: proximal+ / distal–	–0.71	0.30	–0.77	0.36	0.06	–0.21 to 0.34	0.6
zT: anterior+ / posterior–	–0.09	0.21	–0.17	0.23	0.08	–0.10 to 0.26	0.4
Rotation (degree)
xR: anterior+ / posterior– tilt	0.01	0.20	–0.11	0.17	0.12	–0.03 to 0.28	0.1
yR: retroversion+ / anteversion–	0.60	0.73	0.84	0.93	–0.24	–0.94 to 0.47	0.5
zR: valgus+ / varus– tilt	0.00	0.11	–0.04	0.12	0.04	–0.06 to 0.13	0.4

Figure 3. Progression of mean retroversion of the stem centroid with each follow-up period. Error bars represent the 95% confidence interval. P-values are shown at each follow-up period