|Year : 2021 | Volume
| Issue : 1 | Page : 87-89
An unusual variation - Unilateral Gantzer's muscle
K Pushpalatha, NB Pushpa, Deepa Bhat
Department of Anatomy, JSSMC, JSSAHER, Mysore, Karnataka, India
|Date of Submission||09-May-2020|
|Date of Decision||05-Aug-2020|
|Date of Acceptance||16-Oct-2020|
|Date of Web Publication||2-Feb-2021|
N B Pushpa
Department of Anatomy, JSSMC, JSSAHER, Mysore - 570 015, Karnataka
Source of Support: None, Conflict of Interest: None
The accessory head of flexor pollicis longus (FPL) muscle, also known as the Gantzer's muscle, was first described in 1813. The accessory head of FPL muscle significantly varies between studies in its origin, innervation, and relationships to the anterior interosseous nerve and the median nerve. In a 50-year-old male cadaver, we found an additional muscle belly arising from medial epicondyle and joining with the tendon of FPL muscle. The total length of the accessory muscle was 8 cm and was innervated by the ulnar nerve, which is not mentioned in any of the articles in the literature. It is called as Gantzer's muscle as it is taking origin from medial epicondyle. Due to the significant variations in the origin, insertion, innervation, and relationship to the anterior introsseous nerve, median nerve, ulnar nerve, and ulnar vessels of the accessory head of FPL, dependable anatomical knowledge is essential for diagnosis and treatment of nerve entrapment syndromes and avoiding injury during the surgical procedures.
Keywords: Accessary head of flexor pollicis longus, anterior interosseous nerve, flexor digitorum profundus, ulnar nerve
|How to cite this article:|
Pushpalatha K, Pushpa N B, Bhat D. An unusual variation - Unilateral Gantzer's muscle. Int J Health Allied Sci 2021;10:87-9
|How to cite this URL:|
Pushpalatha K, Pushpa N B, Bhat D. An unusual variation - Unilateral Gantzer's muscle. Int J Health Allied Sci [serial online] 2021 [cited 2021 Feb 25];10:87-9. Available from: https://www.ijhas.in/text.asp?2021/10/1/87/308577
| Introduction|| |
Flexor pollicis longus (FPL) is one of the deep muscles of flexor compartment of the upper limb and usually arises from the anterior surface of radius and interosseous membrane. In 1813, Gantzer explained two accessory muscles in the forearm from FPL and the flexor digitorum profundus (FDP); however, this muscle was explained almost a century before by Albinus. Among them, accessory head from FPL is most common. These accessory heads reported to have variable attachments. Gantzer's muscle usaully takes it origin from the medial epicondyle of the humerus or the coronoid process of ulna or the flexor digitorium superficialis (FDS) and gets inserted to FPL. The accessory head of FPL has been reported in different population ranging from 25% to 74%, and among Americans and Asians, it is more than 50%. Relation of Gantzer's muscle with respect to anterior interosseous nerve, median nerve, and ulnar nerve and vessels is debatable. Accessory muscle can pass either superficial or deep to anterior interosseous nerve and ulnar nerve and vessels. Occasionally, accessory muscle is asymptomatic; however, sometimes, it can compress any of these structures present deep to it and cause compression syndrome. Knowledge of the Gantzer's muscle will aid in clinical diagnosis and in surgical approach.
| Case Report|| |
During routine dissection class for MBBS students, in the department of Anatomy, JSS Medical College, we found an accessary head of FPL. Accessary head was arising from the medial epicondyle of humerus (Common flexor origin), superficial to FDS lateral to flexor carpi ulnaris. It was crossing from medial to lateral to join with the tendon of FPL muscle. The total length of the accessory muscle was 8 cm. It had proximal fleshy part measuring 5 cm and slender distal tendon measuring 3 cm. It was running anterior to ulnar nerve and vessels but deep to median nerve. It was innervated by twigs from the ulnar nerve [Figure 1]. It is called as Gantzer's muscle as it is taking origin from the medial epicondyle of humerus.
|Figure 1: Left forearm showing Gantzer's muscle supplied by ulnar nerve supplying Gantzer's muscle. Note the ulnar nerve and vessels passing deep to it. AFPL = Accessory head of flexor pollicis longus, FPL = Flexor pollicis longus|
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| Discussion|| |
Although person with accessory muscles is asymptomatic and found only incidentally either in dissection, imaging, or during surgery, they can be of possible source of clinical symptoms. Knowledge of Gantzer's muscles is important as it can cause vascular compression syndrome or compression of anterior interosseous nerve and median nerve. In Americans and Asians, the frequency of the accessory head of FPL is more than 50% and it seems to be bilateral than unilateral.
Different types of variations of FPL muscle have been reported. It can take origin from the medial epicondyle or from the anterior surface of radius and the adjacent interosseous membrane or from the coronoid process of ulna or its origin merged with the fibers of the FDS [Table 1].,,,,,,,, Insertion of the accessory muscle of FPL also varies. It can get inserted to FPL in 66.6% (1) and 96% (10) and to the FDP in 38.8% (1) and 5.4% (10) and to distal phalanx of the thumb very rarely. Gantzer's muscle inserted in the proximal third of the forearm in 40.4%, in the middle third in 35%, and in the distal third in 24.6% of cases. In the present case, Gantzer's muscle was inserted into FPL in the proximal 1/3 of the forearm.
|Table 1: Variations in the origin of accessory head of flexor pollicis longus,,,,,,|
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In a Korean woman, there were two additional muscles from the proximal part of FDS. Each additional belly had two small bellies: one of them merged into FDP as accessory head and another one continued deep to the median nerve and merged into the FPL as accessory head with a length of 7.7 cm. These accessory muscles were innervated by anterior interosseous nerve.
The relationship of the Gantzer's muscle with neurovascular bundle differs. The muscle can pass deep to median and anterior interosseous nerve and superficial to ulnar vessels and nerve. The accessory muscle passes superficial to median nerve in 90% and deep to it in 10% of cases. In 55.55% of the cases, it was passing deep to anterior interosseous nerve; in 33.33% of cases, it was superficial; and in 11.1% of cases, it was going parallel to anterior interosseous nerve. In the present case, it was passing deep to median nerve and superficial to AIN, ulnar nerve, and vessels.
Nerve supply of Gantzer's muscle is not given much importance, and most of the authors have not mentioned about it except Hafez who mentioned that it is innervated by the anterior interosseous nerve., However, in the present case, it was innervated by ulnar nerve. Accessory muscle is usually asymptomatic, and they are noticed parenthetically during surgery or imaging or during dissection. However, in certain cases, it may produce clinical symptoms due to the compression of the neurovascular structures. Muscle variation is important during decompression fasciotomy for the compartment syndrome of the forearm.
Geographical distribution revealed that Africans most frequently had an accessary head of FPL with a prevalence of 89.3% and North Americans with 50.3% followed by Asians with 44.9% and it was least common in Europeans with a prevalence of 37%. In terms of gender distribution, it is more common in men (41.1%) than in women (24.1%).
Forearm muscular variations can be explained with the embryonic development of the muscles. The anterior compartment muscles of the forearm develop from the flexor mass which consequently divides into superficial and deep layers. FPL develops from deep layer along with FDS, FDP, and pronator quadratus. The existence of accessory muscles could be due to the incomplete cleavage of the flexor mass during development.,, Four fundamental phases also have been described in the ontogenesis of muscle patterns. The accessory head described here could have arisen during Phase 3 when muscle primordia from different layers fuse to form a single muscle. Some muscle primordia disappear through cell death despite the fact that cells within them have differentiated to the point of having myofilaments. Persistence of some cells superficial or deep to anterior interosseous nerve may be responsible for the accessory head of the FPL. One more school of thought is that limb muscles usually formed as two separate elements and then unite to form one muscle. The occurrence of accessory muscle may be due to improper fusion of two elements.
The incidence of an accessory head of FPL is common in the population, and it should be considered as normal than as variation. It is important to note the difference in geographical, racial, and gender distribution although symptomatic nerve compressions are rare; however, patient with anterior interosseous nerve syndrome due to the Gantzer's muscle is also reported.
The variation of the accessory head of the FPL described in the present study differs moderately from those reported in the literature review. It was taking origin from medial epicondyle and joined with FPL proximal 1/3 of the forearm and innervated by ulnar nerve, which is not mentioned in any of the articles in the literature. However, the explained anatomical variations may be anticipated and recognized by surgeons, hence increasing the effectiveness and safety of the surgical procedures.
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Conflicts of interest
There are no conflicts of interest.
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