Abstract: We included four RCTs with 253 participants, all were at risk of bias. One unpublished study evaluated fibrin glue monotherapy compared with Bascom's procedure, two studies evaluated fibrin glue as an adjunct to Limberg flap and one study evaluated fibrin glue as an adjunct to Karydakis flap. For fibrin glue monotherapy compared with Bascom's procedure, there were no data available for the primary outcomes of time to healing and adverse events. There was low-quality evidence of less pain on day one after the procedure with fibrin glue monotherapy compared with Bascom's procedure (mean difference (MD) -2.50, 95% confidence interval (CI) -4.03 to -0.97) (evidence downgraded twice for risk of performance and detection bias). Fibrin glue may reduce the time taken to return to normal activities compared with Bascom's procedure (mean time 42 days with surgery and 7 days with glue, MD -34.80 days, 95% CI -66.82 days to -2.78 days) (very low-quality evidence, downgraded as above and for imprecision). Fibrin glue as an adjunct to the Limberg flap may reduce the healing time from 22 to 8 days compared with the Limberg flap alone (MD -13.95 days, 95% CI -16.76 days to -11.14 days) (very low-quality evidence, downgraded twice for risk of selection, performance and detection bias and imprecision). It is uncertain whether use of fibrin glue affects the incidence of postoperative seroma (an adverse event) (risk ratio (RR) 0.27, 95% CI 0.05 to 1.61; very low-quality evidence, downgraded twice for risk of selection, performance and detection bias and imprecision). There was low-quality evidence that fibrin glue, as an adjunct to Limberg flap, may reduce postoperative pain (median 2 versus 4; P < 0.001) and time to return to normal activities (median 8 days versus 17 days; P < 0.001). The addition of fibrin glue to the Limberg flap may reduce the length of hospital stay (MD -1.69 days, 95% CI -2.08 days to -1.29 days) (very low-quality evidence, downgraded twice for risk of selection, performance and detection bias and for unexplained heterogeneity). A single RCT evaluating fibrin glue as an adjunct to the Karydakis flap did not report data for the primary outcome of time to healing. It is uncertain whether fibrin glue with the Karydakis flap affects the incidence of postoperative seroma (adverse event) (RR 3.00, 95% CI 0.67 to 13.46) (very low-quality evidence, downgraded twice for risk of selection, performance and detection bias and for imprecision). Fibrin glue as an adjunct to Karydakis flap may reduce length of stay but this is highly uncertain (mean 2 days versus 3.7 days; P < 0.001, low-quality evidence downgraded twice for risk of selection, performance and detection bias). Current evidence is uncertain regarding any benefits associated with fibrin glue either as monotherapy or as an adjunct to surgery for people with pilonidal sinus disease. We identified only four RCTs and each was small and at risk of bias resulting in very low-quality evidence for the primary outcomes of time to healing and adverse events. Future studies should enrol many more participants, ensure adequate randomisation and blinding, whilst measuring clinically relevant outcomes.

Plain-language summary: In December 2016 we searched for randomised controlled trials involving participants of any age or sex, whose pilonidal sinus had been treated with fibrin glue, either on its own or with surgery. We found four studies that included 253 participants, the majority of whom were male. Fibrin glue on its own was compared with surgery in one study. In three studies fibrin glue was applied during surgery and compared with surgery on its own. There were problems with the design and conduct of all four studies which mean that their results are very uncertain. It is not known whether fibrin glue on its own affects time to healing and adverse events compared with a type of surgery (Bascom's procedure). Fibrin glue may result in less pain on the first day after the procedure compared with Bascom's procedure. When fibrin glue is used alongside a type of surgery called the Limberg flap it may reduce the healing time by approximately 14 days compared with the surgery on its own, however this finding is highly uncertain as the evidence is very low-quality. It is uncertain whether using the fibrin glue alongside the Limberg flap affects the incidence of a complication called seroma (a collection of fluid) but it may reduce postoperative pain (this evidence is low-quality and therefore quite uncertain) and may reduce time to return to normal activities (low-quality evidence) and length of hospital stay (this was very low-quality evidence and therefore very uncertain). One study evaluated the effect of adding fibrin glue to a type of surgery called the Karydakis flap. It is not clear from this study whether using the glue affects time to healing or the incidence of seroma. Using the fibrin glue with the Karydakis flap may reduce length of hospital stay compared with surgery alone but again this is low-quality evidence. The quality of evidence for all outcomes was low or very low, mainly due to problems with the ways the studies were conducted and also the uncertainty in the results because of the small numbers of participants in the studies. This means we cannot be confident of the effects of fibrin glue on any of these outcomes and more, better quality and larger studies are required. This plain language summary is up to date as of December 2016.