Flexor Pollicis Longus, Anterior View

Description

Running along the anterior compartment of the forearm, the flexor pollicis longus (FPL) belly lies deep to flexor digitorum superficialis and lateral to flexor digitorum profundus, then narrows into a tendon that courses distally toward the thumb. At the wrist, its tendon passes through the carpal tunnel beneath the flexor retinaculum, typically occupying a radial position adjacent to the tendon of flexor carpi radialis (in its own sheath) and near the median nerve. In the thenar region, the FPL tendon continues to the palmar aspect of the thumb and inserts on the base of the distal phalanx, deep to the thenar muscles. Clean anatomy. Anterior rendering of the FPL matters because it clarifies the single-tendon mechanics of thumb interphalangeal flexion and its close relationship to the median nerve within the carpal tunnel. Clinically, this is the tendon that fails in anterior interosseous nerve palsy, producing weakness or loss of flexion at the thumb interphalangeal joint and the classic inability to form a firm tip-to-tip pinch. The same corridor is also where tendon irritation can follow distal radius fractures, carpal tunnel surgery, or inflammatory tenosynovitis, so the spatial relationship to the flexor retinaculum and neighboring tendons becomes more than academic. Use this plate in upper limb anatomy teaching to anchor the deep flexor layer, in hand surgery references discussing carpal tunnel contents and tendon transfers, or in neurology and orthopedics materials covering anterior interosseous syndrome and thumb flexion deficits. It also supports clear labeling in patient education sheets on tendon pathology and post-operative rehabilitation after forearm or wrist procedures. Anatomical accuracy verified by SciePro's Medical Advisory Board.