Table 2.

Repeatability of radiographic double-examination wear measurements for the 3 methods

Analysis method	Mean (range) (mm)	SDdif-intr a	Bias b (±LOA) c(mm)	95% CI d(mm)	p-value e
2D measurements
PW2 f	0.80 (0.28–1.78)	0.26	-0.09 (±0.53)	-0.26–0.08	0.25
PW1 g	1.07 (0.69–1.47)	0.11	0.04 (±0.22)	-0.04–0.11	0.29
EGS-RSA h	0.60 (0.13–1.09)	0.11	0.06 (±0.23)	-0.02–0.13	0.11
3D measurements
PW2	1.12 (0.27–2.20)	0.31	-0.05 (±0.62)	-0.25–0.15	0.61
PW1	1.48 (0.86–2.31)	0.44	-0.03 (±0.87)	-0.31–0.25	0.82
EGS-RSA	0.75 (0.26–1.47)	0.16	0.05 (±0.31)	-0.05–0.15	0.33

^a SD_dif-intra is the random variation within a method comparing double examinations.

^b Bias: systematic variation within a method.

^c LOA: limits of agreement around the bias (95% prediction interval = SD_dif-intra x 1.96).

^d 95% confidence interval for the bias.

^e p value (paired t-test) bias between methods.

^f PW2: PolyWare PE wear analysis using the postoperative and final follow-up radiographs.

^g PW1: PolyWare PE wear analysis using only the final radiographic follow-up radiographs.

^h EGS-RSA: radiostereometric analysis of PE wear using sphere models (the “gold standard”).