International Journal of Scientific & Engineering Research Volume 3, Issue 12, December-2012 1
ISSN 2229-5518
An accessory belly of first lumbrical – a case report
Dr. Sharadkumar Pralhad Sawant1, Dr. Shaguphta T. Shaikh2, Dr. Rakhi M. More3
Abstract : During routine dissection for first MBBS students on 70 years donated embalmed male cadaver in the Department of Anatomy, K. J. Somaiya Medical College, Sion, Mumbai, India, we observed an accessory belly of first lumbrical originating from the radial side of
the most radial tendon of the flexor digitorum profundus (corresponding to the index finger) in the right hand. It passes posteriorly along the radial side of the index finger. The two bellies of first lumbricals join with each other to insert on the extensor expansion near the metacarpophalangeal joint. The photographs were taken for proper documentation. The existence of two bellies of first lumbrical should be kept in mind by surgeons operating on hand.
Key words: Lumbricals, Accessory Belly, Intrinsic Muscles, Flexor Digitorum Profundus, Hand Surgeons.
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HE lumbricals are intrinsic muscles of the hand that flex the metacarpophalangeal joints and extend the interpha- langeal joints (1). There are four of these small, worm-like muscles on each hand. These muscles are unusual in that they have no bony attachment. Instead they attach proximally to the tendons of flexor digitorum profundus and distally to the extensor expansions (2). The first lumbrical is unipennate. It originates from the radial side of the most radial tendon of the flexor digitorum profundus (corresponding to the index fin- ger). It passes posteriorly along the radial side of the index finger to insert on to the extensor expansion near the metacar- pophalangeal joint. The second lumbrical is also unipennate. It originates from the radial side of the second most radial ten- don of the flexor digitorum profundus (which corresponds to the middle finger). It passes posteriorly along the radial side of the middle finger and inserts on to the extensor expansion near the metacarpophalangeal joint. The third lumbrical is bipennate. One head originates on the radial side of the flexor digitorum profundus tendon corresponding to the ring finger, while the other originates on the ulnar side of the tendon for the middle finger. The muscle passes posteriorly along the radial side of the ring finger to insert on its extensor expan- sion. The fourth lumbrical is bipennate. One head originates on the radial side of the flexor digitorum profundus tendon corresponding to the little finger, while the other originates on
the ulnar side of the tendon for the ring finger.
The muscle passes posteriorly along the radial side of the little finger to insert on its extensor expansion. The first and second lumbricals (the radial two) are innervated by the median nerve. The third and fourth lumbricals (the ulnar two) are in- nervated by the deep branch of the ulnar nerve. This is the usual innervation of the lumbricals (occurring in 60% of indi- viduals). However 1:3 (median:ulnar - 20% of individuals) and
3:1 (median:ulnar - 20% of individuals) also exist. The lum- brical innervation always follows the innervation pattern of the associated muscle unit of flexor digitorum profundus (i.e. if the muscle units supplying the tendon to the middle finger are innervated by the median nerve, the second lumbrical will also be innervated by the median nerve) (3). There are four separate sources of blood supply for these muscles: the super- ficial palmar arch, the common palmar digital artery, the deep palmar arch, and the dorsal digital artery. The lumbrical mus- cles, with the help of the interosseous muscles, simultaneously flex the metacarpophalangeal joints while extending both in- terphalangeal joints of the digit on which it inserts. The lum- bricals are used during an upstroke in writing. As a part of the intrinsic musculature, the lumbricals are important for delicate digital movements. They are said to flex the metacar- pophalangeal joints and extend the interphalangeal joints. These are quite unique in their position as they connect the flexors of the digits to the extensors and that both of its at- tachments are mobile. These play a vital role in the precision movements of the hands, along with thenar, hypothenar, and interossei muscles. There are also lumbrical muscles of the foot that have a similar action, though these are of less clinical con- cern.
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• Full name of Authors : Dr. Sharadkumar Pralhad Sawant1, Dr. Shaguphta T. Shaikh2, Dr. Rakhi M. More3
• Institution : 1,2,3Department of Anatomy, K. J. Somaiya Medical College, Somaiya Ayurvihar, Eastern Express Highway, Sion, Mumbai-400 022.
• Telephone no. : 9322061220, 022-22936867
• E-mail : dr.sharadsawant@yahoo.com
During routine dissection for Ist MBBS students on 65 years donated embalmed male cadaver in the Department of Anat- omy, K. J. Somaiya Medical College, Sion, Mumbai, India, we observed an accessory belly of first lumbrical originating from the radial side of the most radial tendon of the flexor digito- rum profundus (corresponding to the index finger). It passed posteriorly along the radial side of the index finger. The two
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International Journal of Scientific & Engineering Research Volume 3, Issue 12, December-2012 2
ISSN 2229-5518
bellies of the first lumbrical joined with each other to insert on the extensor expansion at the metacarpophalangeal joint in the right hand. This additional slip was fleshy in the middle, while it was tendinous at both the ends. The additional slip of origin was innervated by a twig from the lateral branch of the median nerve. However second, third, fourth lumbricals were having normal origin, insertion and innervations. The photo- graphs were taken for proper documentation.
Photographic presentation of an accessory belly of first lum- brical originating from the radial side of the tendon of the flexor digitorum profundus going to the index finger..
Anatomy is a morphological science which cannot fail to in- terest the clinician. Much of the versatility of the human hand depends upon its intrinsic musculature. The lumbrical mus- cles constitute an important part of the intrinsic musculature of the hands. The Lumbricals as a part of the intrinsic muscu- lature are important for its delicate digital movements. Varia- tions in the origin and insertion of the lumbricals are com- mon (4).
Lumbrical muscle variation has been reported in the literature by various authors (5-9). Mehta et al described the anomalous origin of first lumbrical in 2.7% cases they studied (10). In the present case we observed an accessory belly of the first lum- brical originating from the radial side of the tendon of the flexor digitorum profundus to index finger which merged with the first lumbrical for insertion into the radial side of the index finger into the dorsal digital expansion. Additional lumbricals occurring more frequently than a reduction in their number. Origin of lumbricals may be displaced proximally arising from flexor carpi radialis, flexor digitorum superficia- lis, flexor digitorum profundus or flexor pollicis longus. Ac- cessory belly of first lumbrical may arise from flexor pollicis longus, flexor digitorum superficialis, first metacarpal, oppo- nens pollicis or palmar carpal ligament (11). In literature it has been found that the additional fibers from the forearm merged at varying points with the belly coming from the palmar ori- gin and in no case reached the insertion of extensor expansion independently. Hence these are termed as additional forearm origin and not as double lumbricals (10). In the present case the first lumbrical had an accessory belly originating from the
radial side of the tendon of the flexor digitorum profundus to index finger hence termed as double lumbricals (10). First lumbrical and the distal muscle belly for the index finger of the flexor digitorum superficialis have an intimate relationship with each other and have a common phylogenetic origin (12). The articular system in the digits is connected by mechanical links and lumbrical muscles are one of the links of this system that produces dynamic controlled extension of interphalangeal joints (1). Potu BK et al studied an anomalous origin of the lumbrical muscles on South Indian cadavers (13). Haines stu- died flexor muscles of the forearm and hand in the mammals and lizards; he suggested that the FDS in mammals is homo- logous with the intrinsic muscles of the palm, and that it shifts its origin proximally in forearm (14). Further more Koizumi et al. mentioned that the first lumbrical muscle and the distal muscle belly for the index finger of the FDS have an intimate relationship with each other, and have a common phylogenet- ic origin (12). From the above discussion it is quite clear that the additional muscle belly for the first lumbrical as observed in the present case has a phylogenetical significance.
Clinicians and hand surgeons should be aware of such varia- tions of first lumbrical while dealing with the hand, during various surgical procedures.
The authors declare that they have no competing interest.
SPS wrote the case report, performed the literature review & obtained the photograph for the study. RMM performed the literature search and assisted with writing the paper. STS con- ceived the study and helped to draft the manuscript. All au- thors have read and approved the final version manuscript.
All the authors wish to convey thanks to Dr. Arif A. Faruqui for his valuable support. We are also thankful to Mr. M. Mu- rugan. Authors also acknowledge the immense help received from the scholars whose articles are cited and included in ref- erences of this manuscript. The authors are also grateful to authors / editors / publishers of all those articles, journals and books from where the literature for this article has been re- viewed and discussed.
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