|Year : 2020 | Volume
| Issue : 4 | Page : 151-154
Anatomical Study of Accessory Head of Flexor Pollicis Longus and Its Clinical Significance
Bipinchandra Khade1, Gunwant Chaudhari2, Nisha Yadav3, Ashutosh Mangalgiri4
1 Associate Professor, Department of Anatomy, Chirayu Medical College and Hospital, Bhopal, Madhya Pradesh, India
2 Professor, Department of Anatomy, Zydus Medical College, Dahod, Gujarat, India
3 Assistant Professor, Department of Anatomy, Uttar Pradesh University of Medical Sciences, Saifai, Itawah, Uttar Pradesh, India
4 Professor, Department of Anatomy, Chirayu Medical College and Hospital, Bhopal, Madhya Pradesh, India
|Date of Submission||30-Jun-2020|
|Date of Decision||18-Sep-2020|
|Date of Acceptance||22-Oct-2020|
|Date of Web Publication||7-Dec-2020|
Department of Anatomy, Chirayu Medical College and Hospital, Bhopal - 462 030, Madhya Pradesh
Source of Support: None, Conflict of Interest: None
Background: Cases of nerve entrapment are commonly seen in medical practice. The flexor pollicis longus muscle of the front of the forearm sometimes may have an accessory head. The accessory head of flexor pollicis longus muscle (AHFPL) may compress the anterior interosseus nerve (AIN) to cause weakness of the deep muscles of the front of the forearm. The aim of the present study is to find the incidence of AHFPL and to identify its structural relationships to the median nerve and AIN. Methods: A total of sixty upper limbs of thirty embalmed cadavers were dissected and studied for the presence of AHFPL. Parameters studied were incidence of AHFPL, whether it is bilateral or unilateral, its origin and insertion, and its relationship with AIN. Results: AHFPL was found in 16 cadavers (53%). In 7 out of the 16 cadavers (43.75%), AHFPL was bilateral and in 9 out of 16 cadavers (56.25%), AHFPL was unilateral. AIN was located below the AHFPL in 14 cadavers and in 2 cadavers, it was passing above the AHFPL. The nerve supply of AHFPL was through AIN in the 16 cadavers. Conclusion: Knowledge of AHFPL and its relations with AIN may help medical professionals in diagnosis and treatment as this anatomical variation can lead to compression neuropathy.
Keywords: Accessory head of flexor pollicis longus, anterior interosseus nerve, compression neuropathy
|How to cite this article:|
Khade B, Chaudhari G, Yadav N, Mangalgiri A. Anatomical Study of Accessory Head of Flexor Pollicis Longus and Its Clinical Significance. Natl J Clin Anat 2020;9:151-4
|How to cite this URL:|
Khade B, Chaudhari G, Yadav N, Mangalgiri A. Anatomical Study of Accessory Head of Flexor Pollicis Longus and Its Clinical Significance. Natl J Clin Anat [serial online] 2020 [cited 2021 Jan 16];9:151-4. Available from: http://www.njca.info/text.asp?2020/9/4/151/302569
| Introduction|| |
The flexor pollicis longus (FPL) is a muscle in the forearm that originates from the anterior surface of the radius and the adjacent interosseous membrane. It is inserted into the palmar surface of the base of the distal phalanx of the thumb. Accessory head of flexor pollicis longus (AHFPL) muscle was first described by Carl Friedrich Gantzer in 1813 as an accessory muscle in the forearm, emerging as a small belly from the forearm flexors and inserting into the flexor pollicis longus or flexor digitorum profundus (FDP).
The documented presence of AHFPL is 25%–73.6% in different ethnic populations. By the 4th week of intrauterine life, the somatic mesoderm forms ventral and dorsal condensations in the limb buds. Muscles of the front of the forearm develop from ventral condensation and further divide into superficial and deep layers. The deeper layer forms FDP, FPL, and pronator quadratus (PQ) muscles. The incomplete cleavage of deep layer gives rise to AHFPL.
The anterior interosseous nerve (AIN) which is a branch of the median nerve may get involved in entrapment neuropathy, also known as anterior interosseous nerve syndrome (AINS) or Kiloh–Nevin syndrome. This commonly occurring syndrome is characterized by isolated weakness of FPL, FDP tendons of index and middle fingers, and PQ muscle of the forearm. Clinically, it presents as weak flexion of the interphalangeal joint of the thumb and distal interphalangeal joint of the index and middle fingers.
The aim of the present study is to dissect the front of the forearm region to find the incidence of the presence of AHFPL and to identify its structural relationships to the median nerve and AIN.
| Materials and Methods|| |
A total of sixty upper limbs of thirty embalmed cadavers were dissected and studied in the Department of Anatomy, Chirayu Medical College and Hospital, Bhopal, Madhya Pradesh, Central India.
Steps followed in dissection were as follows:
- Incision was given in the ventral aspect extending from the distal arm to the palm
- Skin was reflected, superficial fascia was removed followed by the removal of deep fascia
- The superficial group of the front of the forearm muscles were exposed and observed for normal anatomy as well as variations
- The superficial muscles were cut to expose the deep flexors of the forearm [Figure 1]
- The deep group muscles were observed and studied with respect to their origin, insertion, nerve supply, and any anatomical variations
- The AHFPL when found was examined and studied with respect to the following parameters:
- Whether unilateral or bilateral
- Origin and insertion of accessory heads
- Relation of AIN and median nerves to the accessory heads.
|Figure 1: Deep dissection to show the normal anatomy of muscles of the forearm. A = Median nerve. B = Anterior interosseus nerve. C = Flexor digitorum profundus. D = Flexor pollicis longus|
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| Results|| |
Of the thirty dissected cadavers, AHFPL was found in 16 cadavers (53%). In 7 out of the 16 cadavers, AHFPL was bilateral, that is, 43.75%, and in 9 out of the 16 cadavers, AHFPL was unilateral, that is, 56.25%.
Of the total 16 cadavers, the accessory head originated from the medial epicondyle and was found to be inserted into the fleshy belly of the FPL at variable distances [Figure 2], except in one cadaver (number 10), the AHFPL was inserted into the tendon of the index finger of the FDP of the right upper limb [Table 1] and [Figure 3].
|Figure 2: Variation found in the deep dissection of forearm. A = Median nerve. B = Anterior interosseus nerve. C = Accessory head of flexor pollicis longus. D = Flexor pollicis longus|
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|Figure 3: Variation in deep dissection of the forearm and hand. Accessory head of the flexor pollicis longus found to be inserted in the tendon of flexor digitorum profundus. A = Accessory head of flexor pollicis longus. B = Flexor digitorum profundus tendon slip for index finger|
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|Table 1: Origin and insertion of accessory head of flexor pollicis longus and its nerve supply and relation of the accessory head of flexor pollicis longus with anterior interosseus nerve|
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Out of the 16 cases, AIN was located below the AHFPL, with the exception of the left upper extremity of cadaver no. 4 and the right upper extremity of cadaver no. 16, where it was found to be passing above the AHFPL. The nerve supply of AHFPL was through AIN in the 16 cadavers. Comparison between the right and left extremities showed that out of the 16 cadavers (32 limbs), AHFPL was present in the right extremity in 12 upper limbs (75%) and in left extremity in 11 upper limbs (68.75%) [Table 1].
| Discussion|| |
It is clinically important to study the presence of variations in the muscles of the flexor compartment of the forearm, as these variations serve as etiological factors for many neurological conditions. Various authors have reported various incidences of AHFPL [Table 2]. The lowest incidence of AHFPL was reported in European Caucasians, followed by Asians.,,,,,,,,,
|Table 2: Comparison of incidence of accessory head of flexor pollicis longus with other authors|
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Occurrence of AHFPL was found to be more bilateral (74%) and unilateral (26%) as reported by Mangini and Uyaroglu et al. Mahakkanukrouh et al. also reported incidences of 75.3% bilaterally and 24.7% unilaterally. As per the observations of Oh et al., AHFPL was found bilaterally in 50% and unilaterally in 33% of cases. Jones et al. reported the incidence of AHFPL to be bilateral in 58.4% of cases and unilateral in 33.4% of cases, while the study of Gunnal et al. showed bilateral AHFPL in 71.73%. However, in the present study, AHFPL was found bilaterally in 43.75% and unilaterally in 56.25% of cases.
The most frequent site of origin of AHFPL muscle is from the medial epicondyle of the humerus, which correlated with the findings of Mahakkanukroh et al. and Hemmady et al.
Mahakkanukrow et al. found that AHFPL originated from the medial epicondyle of the humerus in 74.5%, from the coronoid process of the ulna in 23.5%, and from the flexor digitorum superficialis muscle in 2% of cases. Hemmady et al. found that 55.5% of the AHFPL originated from the medial epicondyle of the humerus and 16.6% from the coronoid process of the ulna. As per the findings of Uyaroglu et al., the common site of origin is coronoid process of the ulna (81.5%) followed by the medial epicondyle of the humerus (18.5%). Oh et al. reported coronoid process of the ulna (87.5%) as the common site of origin followed by the medial epicondyle of the humerus (10.4%).
In the present study, the medial epicondyle of humerus is found to be the most common site of origin.
When we discuss the insertion of AHFPL, the most common site documented by various authors is the proximal third of the ulnar border of the FPL tendon according to Jones et al., El Domiaty et al., Rani et al., and Pai et al.
Al-Qattan reported the insertion into the FPL muscle. Mangini suggested the Gantzer muscle as a continuation of the FPL muscle. According to Shirali et al. and Oh et al., AHFPL may have two tendons of insertions. Jones et al. reported three tendons of insertion of AHFPL, out of which two were found inserted into the FPL and one into the FDP.
AINS can be caused by anomalous structures or recurrent injury to the forearm. Also sometimes, the median nerve is compressed between the humeral origin of the accessory head and the flexor carpi radialis. Other causes include pressure due to the brachialis muscle, Struther’s ligament, bicipital aponeurosis, and pronator teres. Paresis or paralysis of the FPL and FDP of the index finger may be caused due to compression of AIN by the AHFPL. Clinically, it is seen as difficulty in flexing interphalangeal joint of the thumb and distal interphalangeal joint of the index finger, that is, difficulty in making “O” using the thumb and index finger, which is known as “Spinner’s sign.”
The pressure of AHFPL may cause weak pinch known as “square pinch deformity” due to weakness of the thumb and index finger muscles.
The presence of accessory heads of muscles should be kept in mind while performing decompression fasciotomy for compartment syndrome of the forearm or anterior approach surgery of the proximal radius and elbow. Fibrous stricture of the AHFPL may occur in some cases of fracture and dislocation of elbow. Hence, involvement of accessory heads of muscles has to be kept in mind whenever treating a flexion deformity of the thumb.
In complete AINS, the entire nerve is below the AHFPL, which leads to weakness in the FPL, in the FDP of the index and middle fingers, and in the PQ muscle. Compression of only the medial branch of the AIN against the FDP causes incomplete AINS because lateral branch of AIN which supplies FPL is not affected. Mahakkanukrauh et al. describes four types of relationships of AHFPL to AIN: (1) AIN lying in front of AHFPL; (2) AIN lying lateral to AHFPL; (3) AIN lying posterior to AHFPL; and (4) AIN lying posterolateral to AHFPL. AINS is associated with Types 3 and 4.
According to Uyragou et al., AIN was anterior to the AHFPL in 3.7%, lateral in 11.1%, posterior in 55.6%, and posterolateral to the AHFPL in 29.6% of cases. EL Domiaty et al. and Mangini et al. found the AHFPL to lie in between the median nerve anteriorly and AIN posteriorly in all cases. However, Dellon and Mackinnon and Al-Qattan observed that the muscle was located behind both the median nerve and the AIN. Shirali et al. documented that the accessory head was behind the median nerve in 91%, anterior to the median nerve in 9%, and was anterior to the AIN in all cases. Gunna et al. stated that in 90.21% of cases, the AIN was lying posterior to AHFPL and in 9.78% of the cases, it passed anteriorly.
In the present study, it was found that in 21 upper limbs, AIN was lying below AHFPL and in 2 upper limbs, it was above the AHFPL.
| Conclusion|| |
Knowledge of AHFPL (Gantzer muscle) and its relations with AIN may help radiologists, neurologists, and orthopedic surgeons while finalizing the diagnosis or during surgeries as the presence of this anatomical variation can lead to compression neuropathy or entrapment syndrome.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2]