Table 2

Subgroup analyses

Group	Number of study	RR and 95% CI	p Value	Heterogeneity (%)	p Value for heterogeneity	p Value for interaction test
Country
Europe	9	1.30 (1.11 to 1.53)	0.001	99.5	<0.001	0.524
USA or other countries	5	1.44 (1.10 to 1.89)	0.007	97.2	<0.001	0.524
Number of patients
>1000	9	1.35 (1.20 to 1.52)	<0.001	98.2	<0.001	0.582
<1000	5	1.28 (1.10 to 1.48)	0.001	87.8	<0.001
Per cent male (%)
>60	2	1.24 (1.12 to 1.37)	<0.001	14.1	0.281	0.383
<60	10	1.35 (1.15 to 1.59)	<0.001	99.5	<0.001
Follow-up duration
10 years or greater	6	1.25 (1.11 to 1.40)	<0.001	97.0	<0.001	0.203
<10 years	8	1.41 (1.22 to 1.63)	<0.001	97.6	<0.001
Adjusted knee injury
Yes	4	1.19 (1.10 to 1.29)	<0.001	60.8	0.054	0.086
No	10	1.39 (1.18 to 1.62)	<0.001	99.5	<0.001
Study quality
8 or 9	6	1.36 (1.11 to 1.66)	0.003	99.7	<0.001	0.535
<8	8	1.27 (1.17 to 1.37)	<0.001	72.5	0.001