Comparative outcomes of combined corticosteroid with low volume compared to high volume of local anesthetic in subacromial injection for impingement syndrome: systematic review and meta-analysis of RCTs

Subacromial impingement syndrome (SIS) is one of the most frequent pathologies of the shoulder, which may cause serious restriction of daily activities and lifestyle changes. Corticosteroid injection (CI) into the subacromial space is a palliative treatment option. Currently, there have been no studies that compare between the different volumes of CI injection. We have conducted a systematic review and meta-analysis to answer our specific study questions: Are high volume (< 5 ml) better than low volume (≥ 5 ml) of CI injection with respect to pain reduction? This systematic review was conducted according to the preferred reporting items for systematic reviews and meta-analyses guidelines. Relevant studies were identified from Medline and Scopus from inception to May 11, 2017 that reported American shoulder and elbow surgeons (ASES) function score, pain visual analog score (VAS), and postoperative complications of either group. Fifteen studies were included for the analysis of high volume (more than or equal 5 ml), and 5 studies were included for analysis of low volume (less than 5 ml). Overall, there were 1101 patients (732 in the high-volume group and 369 in the low-volume group). A pooling of mean VAS and ASES function score was ( N = 557) 2.02 (95% CI 1.52, 2.53), ( N = 190) 82.59 (95% CI 76.92, 88.27) in high-volume group and ( N = 179) 2.60 (95% CI 1.94, 3.26), ( N = 95) 84.65 (95% CI 81.64, 86.82) in low-volume group, respectively. The unstandardized mean difference of ASES and VAS of high volume was − 0.58 (95% confidence interval (CI): − 1.38, 0.22) and − 2.06 (95% CI − 8.35, 4.23) scores lower than low-volume CI in SIS patients, but without statistical significance. A total of 11 studies in the high-volume group and 4 studies in the low-volume group reported adverse effects. The total complication rate per patient was 6.2% (2.3, 10.1%) in the high-volume group and 11.7% (0.3, 12%) in the low-volume group ( p = 0.091). No significant differences were noted for complications. In subacromial impingement syndrome, the corticosteroid injection had acceptable pain and functional outcomes. Higher volume had a lower ASES, VAS, and risk of having complication when compared to lower volume. However, there are no statistically significant differences between groups. Larger, randomized noninferiority or equivalent trial studies are needed to confirm these findings as the current literature is still insufficient. Level of evidence I.