Seven RCTs with 1,126 participants were included in the review.
The overall quality of the studies was poor (mean score 2.47). Quality assessments revealed inappropriate randomisation methods (i.e. alternate weeks) for three of the trials. Heterogeneity was not statistically significant (P>0.05), except in the analysis of technical difficulty (chi-squared 8.73, P<0.05). The results for technical difficulty were reported using the random-effects model.
Major complications did not differ significantly between the closed and open techniques (OR 0.65, 95% CI: 0.15, 2.92). Technical failures and difficulties were significantly higher in the closed group; the OR values were 4.33 (95% CI: 1.96, 9.56) and 5.11 (95% CI: 1.72, 15.19), respectively.
The accuracy of closed and open DPL was comparable: there were no statistically significant differences in the false-negative or false-positive rates between the two techniques.
Procedure time was consistently lower in the closed technique. The mean procedure time was 17.8 minutes in the closed group versus 26.8 minutes in the open group. Sensitivity analyses did not significantly change the summary statistic for all outcomes. The results remained statistically significant for major complications, technical failures and difficulties, irrespective of the inclusion or exclusion of pseudo-randomised trials. The reanalysis using data from only high-quality trials, i.e. those with a Jadad score greater than 3, also did not significantly change the summary statistic.