Background: Piriformis syndrome (PS) is a painful condition caused by entrapment of the sciatic nerve within the piriformis muscle. PS is typically unilateral and mainly occurs related to entrapment of the sciatic nerve. Treatments include physiotherapy, analgesics, anti-inflammatory drugs, behavioral modifications, injection therapy with local anesthetics (LAs) and steroids, epidural injection, botulinum toxin (BT) injection, and surgery.
Objectives: To investigate the efficacy of BT, LA, and corticosteroid (CS) injections in relieving pain in patients affected by PS.
Study design: This systematic review and meta-analysis was conducted according to the "Cochrane Handbook for Systematic Reviews of Interventions" and the "Preferred Reporting Items for Systematic Reviews and Metaanalyses (PRISMA)" guidelines.
Methods: A systematic search was conducted through PubMed, Cochrane, Web of Science, and Scopus through April 2021 for studies investigating the efficacy of BT, LA, or CS injection in improving pain in patients with PS. After screening retrieved studies, data were extracted from included studies and pooled. Overall results were reported as standardized mean difference (SMD) and 95% confidence interval (CI). Analysis was performed using RevMan software version 5.4.
Results: Sixteen studies were included in this systematic review, and 12 of them were included in the quantitative synthesis. The pain scores decreased significantly after treatment with BT (SMD = -2.00; 95% CI [-2.84, -1.16], P < 0.001), LA and CS (SMD = -4.34; 95% CI [-5.77, 2.90], P < 0.001), LA (SMD = -3.73; 95% CI [-6.47, -0.99], P = 0.008), CS (SMD = -2.78; 95% CI [-3.56, -2.00], P < 0.001), and placebo injection (SMD = -0.04; 95% CI [-0.07, -0.01], P = 0.002). BT injection was less effective than LA and CS together (P = 0.006), more effective than placebo (P = 0.001), and similar to LA (P = 0.24) and CS (P = 0.18), when injected alone.
Limitations: A wide variety of study designs were utilized to obtain the largest sample size available. Many of the included studies lack randomization, and some are retrospective in nature. These limitations may introduce bias into the analyzed data and affect the results. Many studies had a low sample size and are of moderate quality, limiting the generalizability of the results. Also, we could not conduct a direct meta-analysis due to the lack of sufficient double-arm studies comparing different types of injection therapies.
Conclusions: In patients with PS, satisfactory pain improvement can be obtained by BT, LA plus CS, LA, or CS injection therapy. Injection of LA plus CS showed the best efficacy.
Keywords: corticosteroids; local anesthetics; meta-analysis; piriformis syndrome; systematic review; Botulinum toxin.