Lumbrical muscle with an additional origin in the forearm
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INTRODUCTION The lumbricals are usually four small intrinsic muscles of the hand. They arise from the tendons of the flexor digitorum profundus (FDP) in the hand and, passing on the radial side, are inserted into the expansion of the extensor digitorum tendons of the four fingers. 1 The first and second lumbricals originate from the radial sides and palmar surfaces of the FDP of the index and middle fingers; the third lumbrical from the adjacent sides of the FDP tendons of the middle and ring fingers; and the fourth lumbrical from the adjacent sides of the tendons of the ring and little fingers. Occasionally, more than four lumbricals are found in one hand. 2 As part of the intrinsic musculature, the lumbricals are important for delicate digital movements. They are said to flex the metacarpophalangeal joints and extend the interphalangeal joints. A rare case of a bipennate first lumbrical muscle with an additional origin arising from the FDP muscle in the distal part of the forearm is presented. RESULTS Twenty-six elderly Chinese cadavers had their upper limbs dis- sected. We focused our study on the intrinsic muscles of the hand. All the intrinsic muscles in the hands of female cadavers were normal. However, we detected an additional origin of the first lumbrical in one hand out of a total of 46 hands (2.2%) from male cadavers examined. We found that the lumbrical muscle to the index finger in the left hand of a 66-year-old male Chinese cadaver was bipennate. The first origin arose from the tendon of the FDP in the hand distal to the flexor retinaculum. The second origin was seen to arise from the same FDP tendon in the distal quarter of the forearm. The muscle passed to the radial side of the index finger and was inserted into the extensor expansion (Fig. 1). No obvious compression of the median nerve of the left hand was visible. The other three lumbricals from the same hand and all the lumbricals of the right hand were normal in appearance. DISCUSSION Variations in the origin and insertion of the lumbricals are common. Any of them may be unipennate (usually innervated by the median nerve) or bipennate (innervated by the ulnar nerve). In the latter case, additional origins commonly arise from the tendons of the flexor pollicis longus (for the first lum- brical) and the flexor digitorum superficialis muscles. In a previous study of 75 cadaver (males and females) hands, Mehta and Gardner reported that only 16% have lumbrical attachments that correspond to the textbook pattern. 3 While the third lumbrical muscle shows the greatest variation in attachments (45.3%), in their study only the second lumbrical has an additional forearm origi- nating from the FDP (2.7%). Eriksen has described a patient whose lumbrical muscle to the third finger arose more proxi- mally than usual from the FDP tendon. 4 ANZ J. Surg. (2001) 71, 301–302 ORIGINAL ARTICLE LUMBRICAL MUSCLE WITH AN ADDITIONAL ORIGIN IN THE FOREARM GURMIT SINGH, BOON-HUAT BAY, GEORGE W. C. YIP AND SAMUEL TAY Department of Anatomy, National University of Singapore, Singapore Background: Although variations in the attachments of the lumbrical muscles have been commonly reported, these have been seen mainly in the Caucasian population. The present study is the first reported case of such an anomaly in a Chinese cadaver in the literature. Methods: The upper extremities of 26 Chinese (23 male and three female) cadavers were examined. Results: Dissection of a male 66-year-old Chinese cadaver has revealed the rare case of a bipennate first lumbrical muscle with an additional origin extending from the distal part of the forearm. Its first origin arose from the flexor digitorum profundus in the hand distal to the flexor retinaculum. The intrinsic muscles in the hands of all the other cadavers were normal. Conclusions: An anomalous origin of the lumbrical from muscles in the forearm has the potential to cause compression of the median nerve in the carpal tunnel. Key words: anomalous first lumbrical muscle, cadaver, carpal tunnel syndrome. Correspondence: B-H. Bay, Department of Anatomy, National University of Singapore, 4 Medical Drive, MD10, Singapore 117597. Email: [email protected] Accepted for publication 5 January 2001. Fig. 1. Anomalous origin of bipennate first lumbrical muscle from the flexor digitorum profundus tendon in the forearm (arrow).
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Transcript of Lumbrical muscle with an additional origin in the forearm
INTRODUCTION
The lumbricals are usually four small intrinsic muscles of thehand. They arise from the tendons of the flexor digitorum profundus(FDP) in the hand and, passing on the radial side, are inserted into theexpansion of the extensor digitorum tendons of the four fingers.1 Thefirst and second lumbricals originate from the radial sides andpalmar surfaces of the FDP of the index and middle fingers; the thirdlumbrical from the adjacent sides of the FDP tendons of themiddle and ring fingers; and the fourth lumbrical from the adjacentsides of the tendons of the ring and little fingers. Occasionally,more than four lumbricals are found in one hand.2 As part of theintrinsic musculature, the lumbricals are important for delicatedigital movements. They are said to flex the metacarpophalangealjoints and extend the interphalangeal joints.
A rare case of a bipennate first lumbrical muscle with anadditional origin arising from the FDP muscle in the distal part of the forearm is presented.
RESULTS
Twenty-six elderly Chinese cadavers had their upper limbs dis-sected. We focused our study on the intrinsic muscles of thehand. All the intrinsic muscles in the hands of female cadavers werenormal. However, we detected an additional origin of the firstlumbrical in one hand out of a total of 46 hands (2.2%) frommale cadavers examined. We found that the lumbrical muscle to theindex finger in the left hand of a 66-year-old male Chinesecadaver was bipennate. The first origin arose from the tendon of theFDP in the hand distal to the flexor retinaculum. The secondorigin was seen to arise from the same FDP tendon in the distalquarter of the forearm. The muscle passed to the radial side of theindex finger and was inserted into the extensor expansion (Fig. 1).
No obvious compression of the median nerve of the left handwas visible. The other three lumbricals from the same hand and allthe lumbricals of the right hand were normal in appearance.
DISCUSSION
Variations in the origin and insertion of the lumbricals arecommon. Any of them may be unipennate (usually innervatedby the median nerve) or bipennate (innervated by the ulnarnerve). In the latter case, additional origins commonly arisefrom the tendons of the flexor pollicis longus (for the first lum-brical) and the flexor digitorum superficialis muscles. In a previousstudy of 75 cadaver (males and females) hands, Mehta andGardner reported that only 16% have lumbrical attachments thatcorrespond to the textbook pattern.3 While the third lumbricalmuscle shows the greatest variation in attachments (45.3%), in theirstudy only the second lumbrical has an additional forearm origi-nating from the FDP (2.7%). Eriksen has described a patientwhose lumbrical muscle to the third finger arose more proxi-mally than usual from the FDP tendon.4
ANZ J. Surg. (2001) 71, 301–302
ORIGINAL ARTICLE
LUMBRICAL MUSCLE WITH AN ADDITIONAL ORIGIN INTHE FOREARM
GURMIT SINGH, BOON-HUAT BAY, GEORGE W. C. YIP AND SAMUEL TAY
Department of Anatomy, National University of Singapore, Singapore
Background: Although variations in the attachments of the lumbrical muscles have been commonly reported, these have been seenmainly in the Caucasian population. The present study is the first reported case of such an anomaly in a Chinese cadaver in the literature.Methods: The upper extremities of 26 Chinese (23 male and three female) cadavers were examined. Results: Dissection of a male 66-year-old Chinese cadaver has revealed the rare case of a bipennate first lumbrical muscle with anadditional origin extending from the distal part of the forearm. Its first origin arose from the flexor digitorum profundus in the handdistal to the flexor retinaculum. The intrinsic muscles in the hands of all the other cadavers were normal.Conclusions: An anomalous origin of the lumbrical from muscles in the forearm has the potential to cause compression of the mediannerve in the carpal tunnel.
Key words: anomalous first lumbrical muscle, cadaver, carpal tunnel syndrome.
Correspondence: B-H. Bay, Department of Anatomy, National University ofSingapore, 4 Medical Drive, MD10, Singapore 117597.Email: [email protected]
Accepted for publication 5 January 2001.
Fig. 1. Anomalous origin of bipennate first lumbrical musclefrom the flexor digitorum profundus tendon in the forearm (arrow).
The carpal tunnel syndrome is caused by compression of themedian nerve as it passes through the carpal tunnel. In a study on26 cadaver upper extremities, Cobb et al. have demonstratedthat the fascial components proximal and distal to the transversecarpal ligament are part of the flexor retinaculum, and areimportant sources of the carpal tunnel syndrome.5 Thus, theyhave included the proximal segment of the deep investing fascia of forearm, the transverse carpal ligament, and the aponeurosisbetween the thenar and hypothenar muscles in defining thepalmar boundary of the carpal tunnel.
Causes of carpal tunnel syndrome with respect to the lumbri-cals include incursion of the lumbrical muscles within the tunnelduring finger movements,6 hypertrophy of the lumbricals,7anatomic variants such as abnormally long lumbrical muscles,4and aberrant tendinous origin of the first lumbrical.8 An anom-alous origin of the lumbrical from the FDP, such as that described inthe present study, has the potential to cause compression of themedian nerve in the carpal tunnel. In any case, the clinician must beaware constantly of such possibilities, although preoperative diag-nosis may be difficult. Treatment depends on the intraoperativefindings and may include incision of the flexor retinaculum,release of the origin of the respective muscle involved, and resectionof the involved muscle.7 In summary, the present case is unique inthat: (i) it is the first reported finding of such an anomaly occurringin a Chinese patient; and (ii) it has a possible association withcarpal tunnel syndrome, as reported previously.4,8
ACKNOWLEDGEMENTS
The technical assistance of Mr P. L. S. Gobalakrishnan, Mrs L. S. Ngand Ms Carolyne Ang is appreciated.
REFERENCES1. Williams PL, Bannister LH, Berry MM et al. Gray’s Anatomy,
38th edn. New York: Churchill Livingstone, 1995.2. Hollinshead WH. Anatomy for Surgeons, Vol. 3, 2nd edn. New
York: Harper & Row, 1969.3. Mehta HJ, Gardner WU. A study of lumbrical muscles in the
human hand. Am. J. Anat. 1961; 109: 227–38.4. Eriksen J. A case of carpal tunnel syndrome on the basis of an
abnormally long lumbrical muscle. Acta Orthop. Scand. 1973; 44:275–7.
5. Cobb TK, Dalley BK, Posteraro RH, Lewis RC. Anatomy ofthe flexor retinaculum. J. Hand Surg. 1993; 18A: 91–9.
6. Cobb TK, An KN, Cooney WP. Effect of lumbrical muscleincursion within the carpal tunnel on carpal tunnel pressure: A cadaveric study. J. Hand Surg. 1995; 20A: 186–92.
7. Robinson D, Aghasi M, Halperin N. The treatment of carpaltunnel syndrome caused by hypertrophied lumbrical muscles.Scand. J. Plast. Reconstr. Surg. 1989; 23: 149–51.
8. Butler B, Bigley EC. Aberrant index (first lumbrical) tendinousorigin associated with carpal tunnel syndrome. J. Bone JointSurg. 1971; 53A: 160–2.
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