These tunnels also have the name of the extensor compartments. An osteofibrous tunnel is a passageway found along synovial joints, which has a bony floor and a fascial roof, with the fascia running in a transverse pattern to help contain neurovascular structures and tendons. The extensor pollicis longus originates on the middle third of the posterior ulnar diaphysis, traverses laterally along the forearm, passes over Lister's tubercle, goes through the third osteofibrous tunnel and travels superiorly to the extensor carpi radialis longus, and extensor carpi radialis brevis then inserts on the base of the distal phalanx of the pollex. The extensor pollicis longus muscle is an extrinsic thumb muscle that belongs to the deep group of dorsal forearm muscles. Overall, it is important to have a good understanding of the EPL to understand the anatomy and potential pathologies, particularly as each relates to the potential compromise of dynamic thumb function. In regards to the latter, the EPL may spontaneously rupture in up to 5% of adults following a non-displaced distal radius fracture or in pediatric patients who had dorsal plating for a displaced distal radius fracture. These pathologies are often seen in association with either medical comorbidities (e.g., rheumatoid arthritis) or as sequelae or associated pathology in the setting of trauma (e.g., distal radius fractures). The EPL tendon is associated with pathologies ranging from stenosing tenosynovitis to spontaneous tendon rupture. Extensor pollicis longus variants are rare, with a prevalence of only 1%. 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. 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.
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