Table 1.

Incidence rate and 10-year risk of osteonecrosis according to age

	Age
	50–59	60–69	70–79	80–89	≥90
Incidence ratea, standardized	2.9	3.9	5.5	7.0	7.4
95% confidence interval	2.9–3.0	3.9–4.0	5.4–5.6	6.9–7.1	7.3–7.5
Casesb, n	1445	4490	3979	2878	633
Person-years, 10,000	569.5	1114.5	709.0	408.1	85.2
10-year risk, %	0.3	0.4	0.5	0.4	0.2
Cases†, n	3985	4228	3344	1691	177
Subjects at baseline, n	1,206,993	986,496	663,860	411,234	75,656

^aIncidence rate/10,000 person-years, standardized for calendar year

^bA different number of cases is tallied for the calculations of incidence rate and 10-year risk because subjects could contribute person-time to more than one age group, but they remained in the same baseline age group