To evaluate the impact of discectomy on back muscles (e.g. multifidus muscle (MM)) morphology in patients with lumbar disc herniation (LDH) following discectomy surgery, address the association of back muscles morphology with pain score preoperatively and post-operatively, and investigate the relationships between the changes from pre- to post-operative back muscles measurements and pain score (primary outcome) and disability score (secondary outcome) change following discectomy if any.We searched three online databases for randomized controlled trials (RCTs) and observational studies. In LDH patients, eligible for discectomy surgery, pre- and post-operative and the changes from pre- to post-operative of back and/or leg pain with Visual Analogue Scale (VAS) and multifidus muscle morphology, were considered as primary outcomes. Cochrane Risk-of-Bias 2 tool and Newcastle-Ottawa Scale (NOS) were used to assess the methodological quality of RCTs and observational studies, respectively. Standardize mean difference (SMD) with 95% confidence intervals (CI) was evaluated. A meta-regression analysis was conducted. GRADE approach was used to summarize the strength of evidence.One RCT and five observational studies were included in the analysis of 489 patients with LDH undergoing discectomy surgery. The mean overall follow-up was 64.9 weeks (6 to 148.7 weeks). There was a significant negative relationship between the change from pre- to post-operative cross-sectional area (CSA) in MM and change in VAS back pain [regression coefficient = -0.01, (95% CI = -0.02, -0.01), p = 0.044] after discectomy surgery. No significant relationship between preoperative CSA in MM and preoperative/post-operative clinical (any of the follow-up periods) scores could be established.The results of this study found very low-quality grade evidence for an association between higher reduction of CSA in MM and less reductions of back pain scores following discectomy surgery for patients with LDH. Due to the heterogeneity and methodological limitations, further studies will improve understanding and aid preoperative counselling.© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.