Effect of Normal Saline Injections on Lateral Epicondylitis Symptoms: A Systematic Review and Meta-analysis of Randomized Clinical Trials

Background: Lateral epicondylitis, or tennis elbow, is a painful degenerative disorder that commonly occurs in adults between 40 and 60 years of age. Normal saline (NS) injections have been used as placebo through a large number of randomized controlled trials (RCTs) focused on the treatment of lateral epicondylitis. Purpose: This meta-analysis of RCTs aimed to assess the therapeutic effect of NS injections on lateral epicondylitis symptoms and compare results with established minimal clinically important difference criteria. Study Design: Systematic review and meta-analysis. Methods: MEDLINE, Embase, Web of Science, and Scopus databases were searched for clinical trials reporting pain and joint function with the visual analog scale, Patient-Rated Tennis Elbow Evaluation, and Disabilities of the Arm, Shoulder and Hand in patients with lateral epicondylitis. The meta-analysis was conducted with a random effects model and generic inverse variance method. Heterogeneity was tested with the I2 statistic index. Results: A total of 15 RCTs included in this meta-analysis revealed a significant improvement in pain (mean difference, 3.61 cm [95% CI, 2.29-4.92 cm]; P < .00001; I2 = 88%; visual analog scale) and function (mean difference, 25.65 [95% CI, 13.30-37.99]; P < .0001; I2 = 82%; Patient-Rated Tennis Elbow Evaluation / Disabilities of the Arm, Shoulder and Hand) after NS injection (≥6 months). Conclusion: NS injections yielded a statistically significant and clinically meaningful improvement in pain and functional outcomes in patients with lateral epicondylitis. New research should focus on better methods to diminish the potential confounders that could lead to this effect because NS injections could mask the real effect of an active therapeutic intervention in RCT. Registration: CRD42019127547 (PROSPERO).