Table 1.

Baseline characteristics of JOS-C study participants at the time of JOS study exit (age 6 y)

Baseline characteristics at age 6 y	Early prophylaxis	Delayed prophylaxis	P
Participants in analysis, n	15	18
Age of prophylaxis initiation, mean (SD), y	1.3 (0.4)	7.6 (3.5)	<.0001
MRI OC damage, n/N (%)
Boys with OC damage	1/15 (6.7)	9/18 (50)	.020
Joints with OC damage	1/89 (1)	9/102 (9)	.021
No MRI damage, eMRI score < 1, n/N (%)
Boys with no damage	11/15 (73)	6/18 (33)	.022
Joints with no damage	85/89 (96)	81/102 (79)	.001
eMRI, median (IQR) of participant joint averages
MRI score	0.08 (0-0.3)	0.6 (0.02-1.7)	.07
OC MRI score	0 (0-0)	1.2 (0.3-3.1)	.05
ABR prior to age 6 y, mean (SD)
Joint ABR	0.7 (0.8)	3.8 (2.8)	.0002
ABR	3.2 (3.1)	14.4 (6.6)	.0072
CPJAS, average per joint, mean (SD)
Physical examination score	1.0 (0.9)	1.7 (1.4)	.094

Numbers expressed as mean (SD) or median (IQR) for continuous variables depending on normal or skewed distribution, and number (percentage) for count variables. Maximum CPJAS score, 31 points per joint; maximum MRI score, 45 per joint; maximum OC score, 36 per joint.

OC, osteochondral.