Comparison 1. Arthroscopic surgery versus placebo surgery.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Pain (lower score=less pain)	4		Std. Mean Difference (IV, Random, 95% CI)	Subtotals only
1.1.1 Up to 3 months	4	309	Std. Mean Difference (IV, Random, 95% CI)	‐0.23 [‐0.45, ‐0.00]
1.1.2 >3 months up to 6 months	3	265	Std. Mean Difference (IV, Random, 95% CI)	‐0.12 [‐0.37, 0.12]
1.1.3 >6 months up to 2 years	3	295	Std. Mean Difference (IV, Random, 95% CI)	‐0.20 [‐0.48, 0.09]
1.1.4 >2 years up to 5 years	1	142	Std. Mean Difference (IV, Random, 95% CI)	‐0.08 [‐0.41, 0.24]
1.2 Function (higher score=better function)	3		Std. Mean Difference (IV, Random, 95% CI)	Subtotals only
1.2.1 Up to 3 months	3	302	Std. Mean Difference (IV, Random, 95% CI)	0.01 [‐0.22, 0.23]
1.2.2 >3 months up to 6 months	2	257	Std. Mean Difference (IV, Random, 95% CI)	0.05 [‐0.20, 0.29]
1.2.3 >6 months up to 2 years	3	293	Std. Mean Difference (IV, Random, 95% CI)	0.10 [‐0.27, 0.47]
1.2.4 > 2 years up to 5 years	1	142	Std. Mean Difference (IV, Random, 95% CI)	‐0.15 [‐0.48, 0.18]
1.3 Knee‐specific quality of life (higher score=better)	2		Std. Mean Difference (IV, Random, 95% CI)	Subtotals only
1.3.1 Up to 3 months	2	188	Std. Mean Difference (IV, Random, 95% CI)	0.31 [0.02, 0.59]
1.3.2 >3 months up to 6 months	1	146	Std. Mean Difference (IV, Random, 95% CI)	0.12 [‐0.20, 0.45]
1.3.3 >6 months up to 2 years	2	188	Std. Mean Difference (IV, Random, 95% CI)	0.23 [‐0.24, 0.70]
1.3.4 >2 years up to 5 years	1	142	Std. Mean Difference (IV, Random, 95% CI)	‐0.02 [‐0.35, 0.31]
1.4 Generic quality of life (higher score=better)	2		Std. Mean Difference (IV, Random, 95% CI)	Subtotals only
1.4.1 Up to 3 months	1	42	Std. Mean Difference (IV, Random, 95% CI)	‐0.56 [‐1.18, 0.06]
1.4.2 >6 months up to 2 years	2	188	Std. Mean Difference (IV, Random, 95% CI)	0.15 [‐0.28, 0.58]
1.5 Participant‐reported success	3	189	Risk Ratio (M‐H, Random, 95% CI)	1.11 [0.66, 1.86]