Table 4.

Titanium ion concentration in erythrocytes, serum, and urine

Treatment group	Median preoperative concentration* (interquartile range)	Median 6-month concentration (interquartile range)	Median year 1 concentration (interquartile range)	Median year 2 concentration (interquartile range)	Intragroup p value||	Intergroup p value¶ (MOP and MOM)	Intergroup p value (MOM28 and MOM 36)
Erythrocyte titanium
MOP†	0.80 (0.50–1.00)	0.90 (0.70–1.20)	1.30 (0.80–1.70)	0.80 (0.60–1.20)	0.391
MOM28‡	1.10 (0.80–1.10)	1.20 (0.90–1.60)	0.80 (0.60–1.33)	0.80 (0.70–1.05)	0.647	0.668
MOM36§	1.00 (0.70–1.28)	1.00 (0.80–1.30)	1.10 (0.70–1.30)	0.90 (0.70–1.70)	0.388	0.204	0.549
Serum titanium
MOP	0.20 (0.08–0.32)	0.79 (0.61–0.87)	0.78 (0.59–1.13)	0.74 (0.63–0.98)	< 0.001
MOM28	0.21 (0.11–0.25)	0.87 (0.74–1.10)	0.84 (0.70–1.00)	0.80 (0.70–1.05)	< 0.001	0.271
MOM36	0.31 (0.16–0.40)	0.71 (0.56–0.92)	0.80 (0.62–1.06)	0.85 (0.72–1.09)	< 0.001	0.257	0.974
Urine titanium
MOP	0.09 (0.06–0.17)	0.14 (0.08–0.24)	0.16 (0.09–0.26)	0.11 (0.07–0.27)	0.192
MOM28	0.10 (0.04–0.23)	0.14 (0.09–0.20)	0.10 (0.07–0.20)	0.11 (0.05–0.13)	0.686	0.479
MOM36	0.12 (0.07–0.23)	0.12 (0.10–0.18)	0.10 (0.07–0.18)	0.07 (0.05–0.16)	0.465	0.164	0.669

*All concentrations are given in μg/L; ^†MOP = patients randomized to metal-on-polyethylene THA; ^‡MOM28 = patients randomized to metal-on-metal, 28-mm THA; ^§MOM36 = patients randomized to metal-on-metal, 36-mm THA; ^||intragroup p value = difference in preoperative and 2-year postoperative titanium ion concentrations within each group using the Wilcoxon test; ^¶intergroup p value = difference in titanium ion concentrations at the 2-year postoperative interval between the metal-on-polyethylene group and each of the metal-on-metal groups and between the two metal-on-metal groups using the Mann-Whitney test.