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An important contributor to thumb function, the extensor pollicis longus (EPL) muscle is an extrinsic thumb muscle that extends and adducts the thumb metacarpophalangeal (MCP) and interphalangeal (IP) joints (see Image. Extensor Pollicis Longus). Innervated by the posterior interosseous nerve, the EPL receives its blood supply from the anterior interosseous artery, posterior interosseous artery, radial artery, and ulnar artery. Extensor pollicis longus variants are rare, with a prevalence of only 1%. The EPL tendon is associated with pathologies ranging from stenosing tenosynovitis to spontaneous tendon rupture.[1] These pathologies are often seen in association with either medical comorbidities (eg, rheumatoid arthritis) or as sequelae or associated pathology in the setting of trauma (eg, distal radius fractures).[2][3][4][5] Regarding the latter, the EPL may spontaneously rupture in up to 5% of adults following a non-displaced distal radius fracture or in pediatric patients with dorsal plating for a displaced distal radius fracture. Overall, it is important to understand the EPL well to understand the anatomy and potential pathologies, particularly as each relates to the potential compromise of dynamic thumb function.[6][7][8][9]