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.