Table 1 Previous studies on anatomical variations and nomenclature of the accessory flexor digiti minimi muscles of the hand
Author | Year | Place | Study design | Names | Origin | Insertion | Function | Innervation | Significance |
|---|---|---|---|---|---|---|---|---|---|
Morrison | 1916 | France | Cadaver (left side) | Accessory flexor muscle of the little finger | The tendon of the palmaris longus | Pisiform and base of the 5th metacarpal bone | Flexion of the little finger with a noticeable inclination toward opposition | The branch of the ulnar nerve and the trunk of the median nerve | The variable palmaris longus muscle is reported to occasionally have a digastric nature, with insertions into the muscles of the thumb or little finger |
Carr | 1977 | UK | Cadaver (right side) | An unusual digastric flexor muscle of the 5th finger | The medial epicondyle of the right humerus | The proximal phalanx of the 5th finger | Flexion of the little finger | N/A | Simultaneously, the absence of the FDM and the unusual diminutiveness of the tendon of the flexor digitorum superficialis were observed |
Sälgeback | 1977 | Sweden | Case | FDMB accessorius | N/A | N/A | Flexion | Deep branch of ulnar nerve | Ulnar tunnel syndrome |
Saadeh | 1988 | Lebanon | Case | An accessory flexor (opponens) digiti minimi muscle | Antebrachial fascia | An additional slip extending to the 5th metacarpal bone | N/A | N/A | Multiple muscle variations can be observed in the same individual and on the same side |
Zeiss | 1992 | USA | MRI (36 normal wrists,16–38 years) | FDMB and anomalous muscles | The fibromuscular arch | ADM | Flexion | Deep branch of ulnar nerve | MRI played a role in diagnosing ulnar nerve abnormalities, ulnar tunnel anatomy and anomalous muscles |
Pribyl | 1994 | USA | Case | Anomalous hand muscle found in the Guyon's canal | Flexor carpi ulnaris | FDMB | N/A | Ulnar nerve | The consideration of ulnar artery thrombosis as a diagnosis arises when a patient reported symptoms such as ulnar neuropathy, hand ischemia, or the presence of a mass in the hypothenar region |
Spinner | 1996 | USA | Plain radiography, MRI (Case, 20, Female) | Anomalous origin of FDMB | Hook of hamate | ADM, neural loop | Flexion | Ulnar nerve | The compression of the medial deep branch of the ulnar nerve by an anomalous tendon, which penetrated through, led to an atypical presentation of ulnar neuropathy |
Wahba | 1998 | Canada | Cadaver | Accessory FDM profundus | Medial intercompartmental septum | The proximal phalanx of the fifth digit | Flexion of the MCP joint of the fifth digit | Ulnar nerve | It possibly affects ulnar nerve function and circulation in the hand |
Uz | 2002 | Turkey | Cadaver (bilateral, 60 male) | Accessory FDMB | Flexor retinaculum | FDMB | Flexion | N/A (close to median nerve) | The existence of accessory muscles holds significance in the context of hand surgery |
Madhavi | 2003 | India | Cadaver (adult male) | Anomalous FDMB | Superficial transverse septum | Guyon's canal superficial to the ulnar nerve and vessels, hypothenar eminence | Flexion | Ulnar nerve | The ulnar tunnel syndrome |
Kobayashi | 2003 | Japan | Cadaver (right hand, female) | Anomalous flexor of the little finger | The midpoint of the volar surface of the flexor retinaculum | The palmar base of the middle phalanx of the 5th finger | Flexion | A branch of the median nerve | The lack of migration of the palmar anlage resulted in the development of an additional muscle belly |
Wingerter | 2003 | USA | Cadaver (right hand) | An unusual origin of the FDMB | The anterior aspect of the transverse fibers of the distal antebrachial fascia | The base of the fifth proximal phalanx | Flexion of fifth MCP joint | The deep branch of the ulnar nerve | Knowledge of anomalous muscles in the hand has important clinical significance in surgery and in determining associated pathology |
Bakinde | 2005 | Switzerland | Cadaver (both hands, 77 male) | Accessory muscle in the hypothenar region | The tendon of the flexor carpi radialis | The ADM muscle into the ulnar aspect of the base of the fifth proximal phalanx | 1. Palmar flexion 2. Rotation of the fifth finger toward the radial side, flexion of the fifth proximal phalanx, and weak abduction of the fifth finger | A branch arising from the main trunk of the ulnar nerve | This muscle variations can cause various clinical symptoms, compression of the ulnar nerve in the Guyon’s canal, Dupuytren contracture, and trauma |
Hill | 2006 | Iran | Cadaver | An unusual muscle of the wrist | The tendon of the flexor carpi ulnaris | The muscle belly of FDM | Flexion | Ulnar nerve | The possibility of compression of the ulnar nerve by such muscles |
Georgiev | 2007 | Bulgaria | Cadaver (left hand, 64-year-old female) | The deep abductor/flexor of the little finger | The lateral belly: lateral part of the flexor retinaculum The medial belly: hamulus of the hamate bone | The anterolateral base of the fifth proximal phalanx | Abduction and flexion | The palmar branch of the ulnar nerve | It causes ulnar nerve compression |
Greiner | 2008 | Wisconsin (USA) | Cadaver (left, 68Â year ol male) | An additional flexor of the fifth digit: FDML | The distal medial of the ulnar tuberosity, distal to the insertion of brachialis muscle | The fourth lumbrical, fifth digital ray of flexor digitorum profundus, base of the distal phalanx | Flexion | The ulnar nerve and dual innervation | The flexor digitorum profundus that arise off the coronoid process, but make no mention of muscular insertions. This muscle is the first identified and described example of FDML |
Cope | 2013 | USA | Cadaver (left hand, female) | A robust FDMB muscle | The proximal attachments were found on the hamate bone and the flexor retinaculum | Its distal attachment was located on the anteromedial surface of the proximal phalanx of the fifth digit | FDMB might have caused effort-related pain for a patient during activities involving grip or prehension | The median and ulnar nerves | These variations could have led to peripheral neuropathy that would otherwise be difficult to explain |
Claassen | 2013 | Germany | Review | Accessory heads of FDM | Flexor retinaculum, antebrachial fascia, long flexor muscles of the forearm | Head of the 5th metacarpal bone, 5th proximal phalanx | Flexion of the proximal interphalangeal joint | Ulnar nerve | It causes ulnar nerve compression or median nerve compression, paresthesia, decreased sensation, and ulnar side of the 4th and 5th finger pain caused by cervical radiculopathy, thoracic outlet syndrome |
Saran | 2014 | India | 100 cadaver upper limbs (80 male and 20 female) | Absence of FDMB and accessory slips | Antebrachial fascia | ADM | Flexion of the little finger at MTP joint and lateral rotation | Deep branch of the ulnar nerve | The existence of an accessory slip was found to potentially induce compression, resulting in ulnar nerve entrapment. Its absence could contribute to hypothenar hammer syndrome through direct compression of the ulnar artery |
Vanguri | 2015 | India | Cadaver (right hand, male) | Accessory head of FDM | The medial side of the palmaris longus tendon | The palmar aspect of base of the fifth proximal phalanx | Flexion of fifth MCP joint | Ulnar nerve | It causes ulnar nerve compression and enhance injury to superficial palmar branch of the ulnar artery |
Beser | 2015 | Turkey | Cadaver (right, 61Â year ol male) | An accessory FDMB or FDML | The tendon of palmaris longus | Medial base of fifth proximal phalanx | Flexion | Ulnar nerve | Ulnar nerve compression, hypovascularity symptoms due to the compression of ulnar artery |
Sailabala | 2015 | India | Cadaver (right hand, male) | Accessory head of FDM | The medial aspect of the palmaris longus tendon, positioned just proximal to the wrist joint | The palmar aspect of the base of the proximal phalanx of the 5th digit | Flexion | The median and ulnar nerves | It modified the kinematics of fifth MTP joint. It had the potential to induce compression, resulting in ulnar nerve entrapment, and its compressive actions might exacerbate injury to the superficial palmar branch of the ulnar artery, potentially causing luminal thrombosis and intimal thickening |
Roman | 2016 | Chile | 2 Cases | The prominent accessory muscles at the distal forearm | Anteromedial side of palmaris longus tendon and antebrachial fascia, flexor carpi ulnaris tendon | ADM, palmar aponeurosis, flexor retinaculum | Flexion of the wrist and fifth finger along with ulnar deviation and abduction against resistance | Ulnar nerve | Accessory muscles have the potential to compress underlying structures in the carpal or ulnar tunnel, resulting in pain and paresthesia |
Moraes | 2018 | Brazil | Cadaver (left hand, adult) | An anomalous FDMB | Hamulus of hamatum and the flexor retinaculum | The base of the proximal phalanx of the fifth finger and the tendon of ADM | Flexion | The deep branch of the ulnar nerve | Ulnar nerve compression, repetitive minor traumas, and muscular hypertrophy |
Moore | 2018 | Canada | Cadaver (left hand, 83 male) | Accessory FDMB | Distal tendon of the palmaris longus | Base of the proximal phalanx of the fifth digit | Flexion | A branch of the ulnar nerve | Accessory muscles and their aberrant innervation patterns have the potential to complicate surgical procedures, leading to the compression of arteries and nerves, ultimately causing upper limb pain and paresthesia |
Nation | 2019 | USA | Cadaver (right hand, 94-year-old female) | The additional flexor muscle (FDML) | The distal two thirds of antebrachial fascia | It passed through Guyon’s canal | It is not clear if muscle function was affected | Ulnar nerve | The compression of Guyon’s canal, median, and ulnar nerves |
Patil | 2021 | USA | Cadaver hands (30) | FDM | The fibrous arch-like connection between FDM and the ADM The FDM muscle origin was situated radial to the origin of the ADM muscle by an average of 14 mm (range, 8–24 mm) the convex surface of the hook of hamate and flexor retinaculum | The distal part was fused to the ADM (55%) inserts onto the ulnar side of the base of the proximal phalanx of the little finger | Its radially located origin was a positional advantage while being used for opposition | The deep branch of the ulnar nerve | FDM muscle was absent in 33% of hands It had positional advantage over the ADM for opponensplasty FDM can be transferred if it is found to be suitable in surgery |