Paxton 1995

Methods	Double‐blind, placebo‐controlled, randomized clinical trial Sequence generation "at random", but not described Follow‐up: 12 months
Participants	Participants: 70 adults from a university setting in Belfast, Northern Ireland Operation: vasectomy for contraception 2 groups, size: 70 total, (group size not given) Age: years (range ): 35 years (range 26‐45), 34 years (28‐45) Men/women: 70/0 Remarks: in the intervention group, body sides were randomized to receive treatment or placebo.
Interventions	Group 1a (intervention, body side treated): GA, intraop: bupivacaine (0.5% 1 mL) injected into the lumen of the vas deferens, post‐op NSAID Group 1b (intervention, placebo body side): GA, intraop: normal saline injected into the lumen of the vas deferens, post‐op NSAID Group 2 (control, both sides): GA, intraop: no injection, post‐op NSAID Adjuvants: none Immediate post‐op pain control: significantly improved
Outcomes	Dichotomous: testicular discomfort at 12 months Continuous: duration of testicular discomfort Secondary: none
Notes	No available contact info to email study author to inquire about study sponsorship Funding sources: source of funding not reported Conflicts of interest: no conflict of interest statement given
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "randomly....at random..," but exact method of sequence generation not reported. Still, with excellent description of allocation concealment and blinding, we judge that bias is unlikely.
Allocation concealment (selection bias)	Low risk	Allocation was done after education and enrolment, (it remains unclear when the vas deferens side was randomized, but this is unlikely to cause bias.) Bias is unlikely.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Bias during operation by non‐blinded providers possible, e.g. by administering additional fentanyl, but not very likely.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Quote: "all the replies were analysed by one of the authors who was unaware of the treatment".
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "the questionnaire was valid for 61 (91%) patients only." Six participants did not respond and "...three were excluded because of development of wound infection and scrotal haematoma." A per‐participant analysis was performed, withdrawals and attrition were reported, but allocation to groups or subgroup was not reported. Bias is likely, but unlikely to change the result of the study.
Selective reporting (reporting bias)	Low risk	No protocol available but all specified outcomes were reported on.
Null bias	Low risk	Quote: "the VAS scores for pain on days 1..were significantly lower on the side of the bupivacaine infiltration in the treatment group compared with the saline side of this group and the control group"