Table 1. ONKR values and ROC curve analysis of ^99mTc-annexin V in the control group and the infected group.

		ONKR values				ROC curve analysis
		Control group	Infected group	P	AUC	Cutoff	Se(%)	Sp(%)	Ac(%)
7 days after surgery	1 hour p.i.	1.98 ± 0.19	2.09 ± 0.23	0.42	0.653	1.89	83.3	50	37.5
	4 hours p.i.	1.79 ± 0.15	1.99 ± 0.43	0.31	0.639	1.9	66.7	83.7	80
21 days after surgery	1 hour p.i.	1.42 ± 0.29	1.84 ± 0.29	0.03	0.833	1.44	100	50	66.7
	4 hours p.i.	1.53 ± 0.48	2.19 ± 0.34	0.02	0.917	1.86	100	83.3	85.7

ONKR: Operated to Normal Knee activity Ratio; p.i.: post ^99mTc-annexin V injection; In the calculation of sensitivity (Se), specificity (Sp) and accuracy (Ac), the scan was considered positive for infection when ONKR value was > cutoff; The ONKRs of the infected group were significantly higher than those of the control group at 21 days after surgery, especially in delay phase.