Anatomy Of the Flexor Pollicis Longus Muscle - Everything You Need To Know - Dr. Nabil Ebraheim

Dr. Ebraheim’s educational animated video describes the anatomy of the flexor pollicis longus muscle.

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The flexor pollicis longus is one of the three deep flexors of the muscles of the forearm. The flexor digitorum profundus, the flexor pollicis longus, and the pronator quadratus (distal third of forearm) muscles lie in the deep forearm compartment. These muscles run underneath the flexor digitorum superficialis muscle. The flexor pollicis longus arises from the anterior surface of the radius and the interosseous membrane. The flexor pollicis longus muscle runs through the carpal tunnel. It is the most radial structure located within the carpal tunnel. The flexor pollicis longus muscle runs through the carpal tunnel. It is the most radial structure located within the carpal tunnel. The FPL is inserted into the palmar aspect of the base of the distal phalanx of the thumb. The FPL is innervated by the median nerve through the interosseous nerve. The FPL helps in doing the “O.K.” sign. Loss of the function of the anterior interosseous nerve will lead to the inability to do the “O.K.” sign. The action of the FPL is flexion of the thumb at the MCP and IP joints. Flexor pollicis longus rupture is more common in Volar plating of the distal radius. Rupture of the tendon is associated with plate placement distal to the watershed area, which is the most volar margin of the radius closest to the FPL tendon. Sharp screw edges and prominent plates may be the reason for rupture of the flexor pollicis longus tendon. Adequate covering of the volar plate by the pronator quadratus muscle may help in decreasing the incidence of flexor pollicis longus tendon rupture. The Gantzer muscle is an accessory head of the FPL which is found in about 60% cadavers. The Gantzer muscle can be involved in compression neuropathy of either the median nerve or the anterior interosseous nerve. The origin of this accessory muscle is variable. The muscle inserts distally into the ulnar border of the FPL in about 100% of cases. The Gantzer muscle is innervated by the anterior interosseous nerve. In summary, the Gantzer muscle is an accessory head of the FPL muscle that can cause compression of the median nerve or the anterior interosseous nerve.