Table 3.

Incidence of hemophilic arthropathy by interval-level characteristics

			Number of analytic units	Joint-years of follow-up	Number of HA progression events	Incidence rate per 1,000 joint-years of follow-up
Interval-start Arnold–Hilgartner stage	Arnold–Hilgartner stage	0	517	7,574	22	2.9
		I	21	164	6	36.6
		II	41	544	23	42.3
		III	47	353	43	121.9
	Regular prophylaxis at first visit to our institute	No	412	3,797	54	14.2
		Yes	456	4,837	40	8.3
Laterality		Right	295	4,280	52	12.1
		Left	288	4,354	42	9.6

Incidence of progression to hemophilic arthropathy, defined as reaching Arnold–Hilgartner stage ≥ IV. Values are shown by analytic characteristics. Observation intervals were created when treatment status or radiographic status changed; therefore, counts for interval-start Arnold–Hilgartner stage and prophylaxis status represent analytic intervals and do not equal the number of unique joints shown in Table 2. Laterality is shown at the joint level. Incidence rates are expressed per 1,000 joint-years of follow-up. HA, hemophilic arthropathy