Accessory Head of the Flexor Pollicis Longus: A Cadaveric Study on the Gantzer’s Muscle

Abstract

Introduction: The anterior interosseus nerve syndrome is a compression neuropathy affecting the anterior interosseus nerve, resulting in motor weakness of the long tendons to the index finger and thumb. Of the many conditions leading to this syndrome, one of the more common yet most overlooked aetiologies is the presence of accessory head of the flexor pollicis longus muscle, also called the Gantzer’s muscle. Even though numerous studies have been done in both Indian and international populations regarding the frequency of the Gantzer’s muscle, there are hardly any studies involving the South Indian population. Aim: To analyse the frequency and morphology of the Gantzer’s muscle in the sub-population of Malabar region, Kerala. Materials and Methods: This descriptive observational study was performed in Department of Anatomy at Malabar Medical College, Atholi, Kerala, India, from July 2021 to August 2021. Study included 60 upper limbs from the cadavers provided for undergraduate medical education. In the limbs where the muscle was identified, parameters such as proximal and distal attachments, shape and length of muscle and tendon, relation to adjacent median and anterior interosseus nerves were studied. Frequencies of each of these parameters were analysed using Statistical Package for the Social Sciences (SPSS) software version 21.0. Percentages obtained were compared with existing studies. Results: The Gantzer’s muscle was found in 28 of the 60 limbs dissected. It was more common on the right side (17 limbs), and the most common origin was the medial epicondyle (53.6%). All the cases identified were inserted onto the ulnar aspect of the Flexor Pollicis Longus tendon, mostly in the upper third. In all cases, the Median Nerve was superficial and the Anterior Interosseus Nerve was deep to the accessory head. In majority of the cases, the Anterior Interosseus Nerve was related to the posterior aspect of the belly of the Gantzer’s muscle (82.1%). Conclusion: Clinicians and surgeons should be conscious of the possibility of the Gantzer’s muscle being the aetiology, in cases of isolated Anterior Interosseus nerve palsies.