Accessory Head Of Flexor Pollicis Longus Research Articles

Incidence and Morphology of Accessory Head of Flexor Pollicis Longus in Telangana, India

Introduction: Flexor Pollicis Longus (FPL) may have accessory slips which arise from lateral or medial border of coronoid process of ulna and medial epicondyle of humerus. The accessory slip of FPL is known as Accessory Head of Flexor Pollicis Longus (AHFPL) or Gantzer’s Muscle. Aim: To study the incidence and morphology of AHFPL and the relationship of AHFPL with Median Nerve (MN) and Anterior Interosseous Nerve (AIN) in Telangana population. Materials and Methods: The present study was an observational study, conducted on 25 cadavers (21 male, 4 female) for a period of 18 months (July 2019-December 2020) in Department of Anatomy, Osmania Medical College, Hyderabad, Telangana, India. The cadavers which were used for dissection by first year MBBS students were included in the present study and the cadavers with scars, deformities and with congenital anomalies were excluded from the present study. Results: In the present study, AHFPL was found in 58% upper limbs. It was bilateral in 40%, unilateral in 18% upper limbs. The shape of AHFPL was fusiform in majority of (86.2%) upper limbs. It originated from the coronoid process of ulna in 62% and from medial epicondyle of humerus in 38% upper limbs, inserted by joining with tendon of FPL. The AHFPL was innervated by AIN in all the cases and this nerve was located posterior to AHFPL in majority of (83%) upper limbs, posterolateral in few (17%) upper limbs. The MN was related anterior to the AHFPL in most of the upper limbs. Conclusion: In the present study, AHFPL was found in 58% upper limbs. Bilateral occurrence (40%) was common than unilateral (18%). The presence of AHFPL can cause AIN syndrome, pronator teres syndrome. The knowledge of AHFPL would be useful for both physicians and surgeons to know the aetiology and management of compression neuropathy/nerve entrapment syndrome.

An unusual variation - Unilateral Gantzer's muscle

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.

A case of double Gantzer's muscle and its possible role in nerve entrapment

Department of Anatomy and Biology, Osaka Medical College, Takatsuki, Osaka, JapanAnomalous variants are essential for teaching bothanatomists and surgeons. Muscle anomalies of theupper extremity are recognized causes of periph-eral nerve disorder (Jones et al., 1997; Pai et al.,2008). Gantzer’s muscle (GM) or accessory head offlexor pollicis longus (FPL) has been implicated inKiloh-Nevin (i.e., ‘‘anterior interosseous’’ nerve)syndrome (Rask, 1979; Oh et al., 2000; Mahakka-nukrauh et al., 2004; Pai et al., 2008). Moreover,both GM and fibrous arch of flexor digitorum sub-limes (FDS) are considered as possible anatomicalfactors for median nerve (MN) entrapment neurop-athy (Lee and LaStayo, 2004; Bilecenoglu et al.,2005). Two GMs (Fig. 1) were detected in the rightforearm of an old Japanese male cadaver duringpractical anatomy course for undergraduate medi-cal students at Osaka medical college. Thesemuscles were present at two different anatomicalplanes. One of them, the deep GM (DGM), waslarger, voluminous in shape, and originated fromthe medial epicondyle of humerus and inserted intothe ulnar side of FPL muscle at the junctionbetween proximal and middle thirds of forearm.The second one or superficial GM (SGM) wassmaller and fusiform in shape and arose from theundersurface of humeroulnar head of FDS muscleand terminated distally into the FPL close and lat-eral to insertion of DGM. The MN passed superficialto the deep head of pronator teres (PT) musclewhere it gave the anterior interosseous nerve(AIN) just distal to the lower border of the crossedmuscle. The AIN arose from the lateral side of MNand both nerves coursed distally between twomyo-fibro-tendinous layers; the fibrous arch of FDSand SGM superficially and the DGM deeply. It hasbeen reported that the arcuate ligament of Fearnand Goodfellow is the fibrous tissue that blends to-gether from the PT and FDS muscles and can catchboth the AIN and MN in some patients sufferingMN compressive neuropathy (Rask, 1979). In ourcase, the origin of AIN from the radial side of MNwas reported by Ashworth et al. (1997). The AINdescended radial to the DGM, gave branches toboth SGM and FPL, sank deep to the tendon ofSGM and then passed deep to FPL where it reap-peared again medial to the latter muscle on theinterossous membrane. The manner of proximaland distal attachments, the shape as well as theinnervation of GMs, have been reported by others(Oh et al., 2000; Mahakkanukrauh et al., 2004;Pai et al., 2008). It seems that both MN and AINwere caught in intermuscular tunnel roofed by theSGM and FDS and floored by the DGM. The pres-ence of both DGM and SGM in addition to fibrousarch of FDS may be involved in MN and AIN com-pressive neuropathy. Moreover, the presence oftwo GMs may result in restricted movement of FPLand subsequent pain in lower forearm as reportedby others (Ryu and Watson, 1987; Pai et al.,2008). On the other hand, the GMs may be impor-tant in local transfers for restoring function in mul-tiple nerve palsies (Pai et al., 2008). The accessoryheads of the flexor muscles have been described inprimates and other mammals (pigs, foxes, andmarmots) as a muscle belly that connects themedial epicondyle origin of the FDS with the moreor less differentiated deep flexors muscle. Theflexor muscles of the forearm that develop fromthe flexor mass divide into two layers, superficialand deep. The FDS, FPL, and flexor digitorum pro-fundus originate from the deep layer. The existenceof accessory muscles connecting the flexor musclescould be explained by the incomplete cleavage ofthe deep layer of the flexor mass during develop-ment (Jones et al., 1997). This is the first report inthe literature regarding the presence of two GMsarising from different proximal attachments at two

Anatomical study of the accessory head of the flexor pollicis longus and the anterior interosseous nerve in Asians.

Anterior interosseous nerve palsy is known to occur uncommonly due to the compression of the nerve by the accessory head of flexor pollicis longus (AHFPL). This study was conducted to investigate the prevalence and origin of the AHFPL and the topographical relationship between the AHFPL and the anterior interosseous nerve in Asians. The AHFPL was present in 48 of 72 arms examined (66.7%), a majority of which originated from the coronoid process. The anterior interosseous nerve was observed to arise from both the medial and posterior aspects of the median nerve. The topographical relationship between the anterior interosseous nerve and the AHFPL was classified into three types depending on if the anterior interosseous nerve crossed the muscular part, or the tendinous part of the AHFPL, or coursed lateral to the AHFPL. The case in which the anterior interosseous nerve crossed the muscular part of the AHFPL occurred most frequently in the current study. The types in which the anterior interosseous nerve may be compressed were also discussed.