Morphometry of accessory head of flexor pollicis longus: A cadaveric study

Background: The flexor pollicis longus muscle is present in the deep layer of the front of the forearm. Sometimes an extra head arises from the ulnar coronoid process which is known as the Accessory Head of Flexor Pollicis Longus (AHFPL), also known as Gantzer's muscle. Aim and Objectives: The present study was conducted to know the morphological features and morphometry of the AHFPL with its clinical importance. Material and Methods: The present study was conducted on 50 upper limb specimens (25 right and 25 left) of 23 male and 2 female cadavers, fixed in 40% formalin collected from the donated bodies under voluntary body donation program in the Anatomy department, JSS medical college, Mysore. The forearm was dissected, the deep group of muscles was exposed, and the flexor pollicis longus muscle was studied. If an extra head was present, its shape, origin, insertion, nerve supply, and blood supply were noted. Its muscular and tendinous length and breadth were measured using the digital vernier caliper. Result: Among 50 specimens, accessory head was present in 14 (28%) specimens. Most commonly the muscle was originating from the medial epicondyle and less common was from the coronoid process. Most commonly observed insertion was to the tendon of the flexor pollicis longus. All were supplied by the anterior interosseous nerve. The length of the muscle belly was ranging from 8.2 cm to 15.1 cm and the mean was 11.54 cm. The tendon length ranged from 0.2 to 6.44cm and the mean was 2.33cm. The thickness was ranging from 2.1mm to 8.8 mm. and the mean was 4.57mm. Conclusion: The accessory head of flexor pollicis longus is not a rare occurrence. The anatomical knowledge of this variation plays an important role in the diagnosis and surgical intervention of nerve entrapment syndrome like anterior interosseous nerve syndrome.