Psoas Compartment Block Versus Medial Branch Block for Low Back Pain: A Narrative Review of Anatomical Targets, Clinical Evidence, and Patient Selection

Background: Low back pain (LBP) remains the leading global cause of years lived with disability, and image-guided nerve blocks occupy a central position in its diagnostic and therapeutic pathway. Two paraspinal targets separated by only a few centimetres of tissue address entirely different neural territories: the medial branch of the lumbar dorsal ramus, addressed by the medial branch block (MBB), and the ventral rami of L1–L4 that form the lumbar plexus within psoas major, addressed by the psoas compartment block (PCB). Despite this anatomical proximity, the two techniques have matured within largely separate literatures—interventional pain medicine for the MBB and regional anaesthesia for the PCB—and have never been compared head-to-head in a randomised trial. Methods: This narrative review searched PubMed/MEDLINE, Embase, Scopus, the Cochrane Library, and Google Scholar to 1 August 2026 and synthesises evidence on the anatomical rationale, technical performance, effectiveness, and safety of both blocks as they apply to patients presenting with LBP. Results: The MBB is supported by extensive diagnostic-accuracy data and guideline endorsement for facet-mediated axial pain, but requires controlled blocks to constrain false-positive rates and confers only short-lived therapeutic benefit. The PCB reliably produces dense lumbar plexus analgesia and has a well-defined perioperative role, yet direct evidence in chronic LBP is confined to small series, and its complication profile—including epidural spread and retroperitoneal haematoma—is materially more demanding. Conclusions: We propose a phenotype-driven selection framework in which the MBB serves posterior-element axial pain while the PCB is reserved for plexus-mediated, hip–spine overlap, and perioperative indications, and we outline the comparative studies required to test it.