Seven RCTs (involving 726 digits) were included in the review. One trial achieved a level A quality rating; the remaining 6 trials were considered to be level B, largely due to inadequate reporting of randomisation and allocation concealment.
Palmar blocks versus dorsal blocks.
Six trials (involving 609 digits) were pooled, revealing no significant difference in injection pain between palmar and traditional blocks. A large degree of heterogeneity (I2=80.6%) was reported. The differences remained statistically non significant when separate pooling was carried out for trials of transthecal block (I2=86.2%) (4 trials) and single subcutaneous palmar injection block (I2=0%) (3 trials), and when heterogeneity was explored according to the use of plain lidocaine (I2=82.5%) ( 5 trials) or buffered lidocaine. The only significant difference for distribution of anaesthesia was found in favour of the traditional block (RR 10.71, 95% CI: 3.95, 29.05, p<0.00001; I2=0%) (2 trials) compared with palmar block for the proximal phalanx only. There were no significant differences in pain scores resulting from the sensitivity analysis.
Transthecal blocks versus subcutaneous blocks.
Four of 6 trials (involving 304 digits) reporting injection pain were pooled, showing results in favour of subcutaneous blocks (WMD 0.76 cm, 95% CI: 0.06, 1.46, p=0.03). There was high heterogeneity (I2=81.7%) which was not reduced when the subcutaneous blocks were subdivided. However, when one study using buffered lidocaine was removed from the analysis, the effect size was increased to 0.90 cm (95% CI: 0.10, 1.70, p=0.03) and heterogeneity was reduced (I2=75.3%). The comparison of transthecal block with single subcutaneous palmar block at the level of the A1 pulley in one trial revealed no statistically significant difference in terms of distribution of anaesthesia.