We report a case of bilateral reversed palmaris longus muscle (PLM). The muscle
was tendinous in its upper portion and muscular in its lower portion in both
arms. This rare variation has been mentioned only once in the literature as
a surgical finding. According to the literature, a reversed PLM may cause a compartment syndrome in the wrist area, carpal tunnel, and Guyon&#8217;s syndrome.
The described variation is also useful to the hand surgeon as a tendon graft,
a tendon for transfer, or as an anatomical landmark for operations at this area

Cantin, M.

Inzunza, O.

Macuer, M.

Munoz, A.

Saez, J.

Salgado, G.

English

Via Medica Journals

Folia Morphol. Vol. 71, No. 1, pp. 52–55Copyright © 2012 Via MedicaISSN 0015–5659www.fm.viamedica.plC A S E   R E P O R T52Address for correspondence: Dr. M. Cantín, MSc, Faculty of Medicine, Department of Integral Odontology, Universidad de La Frontera,Manuel Montt 112, Temuco, Chile, tel: +56045235574, e-mail: mcantin@ufro.clBilateral reversed palmaris longus muscle:a rare anatomical variationG. Salgado1, M. Cantín2, O. Inzunza1, A. Muñoz1, J. Saez1, M. Macuer11Department of Normal Anatomy, Pontificia Universidad Católica de Chile, Faculty of Medicine, Santiago, Chile2Department of Integral Odontology, Doctoral Program in Morphological Sciences, Faculty of Odontology, Facultyof Medicine, Universidad de La Frontera, Temuco, Chile[Received 8 September 2011; Accepted 23 October 2011]We report a case of bilateral reversed palmaris longus muscle (PLM). The mus-cle was tendinous in its upper portion and muscular in its lower portion in botharms. This rare variation has been mentioned only once in the literature asa surgical finding. According to the literature, a reversed PLM may cause a com-partment syndrome in the wrist area, carpal tunnel, and Guyon’s syndrome.The described variation is also useful to the hand surgeon as a tendon graft,a tendon for transfer, or as an anatomical landmark for operations at this area.(Folia Morphol 2012; 71, 1: 52–55)Key words: palmaris longus muscle, reversed muscle, anatomicalvariation, forearmINTRODUCTIONThe palmaris longus muscle (PLM) is a fusiformand thin muscle that lies medial to the flexor carpiradialis (FCR) muscle. It shares a common origin withthe flexor superficialis digitorum (FSD) muscle, theflexor carpi ulnaris (FCU) muscle, and the FCR, in themedial epicondyle of the humerus. It then projectstoward the distal and lateral regions, exhibiting mus-cular qualities up to two thirds of the length of theforearm, finally ending in a long and slender tendon,which passes anteriorly to the flexor retinaculum. Itis inserted into the distal half of the anterior surfaceof the palmar aponeurosis (although occasionally,into the retinaculum) [7, 15]. It frequently extendsby means of a tendinous slip toward the muscles ofthe thenar region [9]. It is placed just beneath theskin, under subcutaneous adipose tissue and the deepfascia of the forearm — its deep surface in relationwith the FDS muscle, between the FCU and the FCRmuscles. It is functionally redundant [14, 15]. Becauseof this and its easy accessibility, it is frequently usedas a tendinous graft or as a transference tendon withthe thumb to obtain opposition and abduction [15].The PLM is extremely variable. Its most frequentvariation is agenesis, reported in 12.8% of the po-pulation [10, 15]. Other variations include differenc-es in shape and position described as central, in-verted, bifid, duplicated [11], and even triplicated[7, 15]. These variations affect 9% of the popula-tion [10]. The close topographic relation betweenthe PLM and the median nerve makes such anatomi-cal variations a common cause of median nerve en-trapment and compression [5, 6].A PLM displaying a tendinous proximal segmentand a muscular distal segment was first described asan inverse PLM. It was later renamed to its currentname, reversed PLM [14]. Many surgeons and anato-mists have reported cases in which patients that en-dure repetitive tasks suffer from median nerve com-pression because of the presence of a reversed PLM[1, 2, 6, 8, 12, 15]. In such cases, surgical excision ofthe reversed muscle proved to be the appropriatetreatment to relieve related symptoms [2, 3, 7, 9, 15].Schuurman and van Gils [12] reported that, in pa-tients diagnosed with median nerve compression, mag-netic resonance imaging (MRI) could be used to unilat-53G. Salgado et al., Bilateral reversed palmaris longus muscleerally determine if a reversed PLM is the source of sucha condition instead of an inflammation in the carpal tun-nel, which would normally be expected during mediannerve compression. Thus, muscular variations, such asthe reversed PLM, should be considered when evaluat-ing both median and ulnar nerve neuropathy in thewrists. Most cases of reversed PLM descriptions and ex-tirpations have been unilateral, on the right forearm [15].The existence of a bilateral reversed PLM has onlybeen described once in the literature as a clinical find-ing, in a patient showing symptoms indicating tem-porary median nerve compression in both forearms.In this study, we describe an inverse PLM found bilat-erally on a cadaver and analyse its clinical significance.CASE REPORTDuring a routine educational dissection at thePontificia Universidad Católica de Chile MedicalSchool’s Anatomy department, the flexor muscleson the forearms of a 78-year-old male cadaver whosedeath was caused by a pulmonary emphysema wereexposed. An anatomical variation in the PLM wasfound on both forearms: the tendinous portion wasoriented toward the proximal end, and the muscu-lar portion was oriented toward the distal end,a condition described as a reversed PLM.The reversed PLMs on both forearms were dis-sected along with their surrounding structures, ex-posing the PLM’s proximal insertion into the humeralmedial epicondyle, its musculotendinous junction,and its distal insertion into the palmar aponeurosison the hand. The proximal and distal anatomicalstructures were identified, and all relevant anatom-ical relations were described (Figs. 1A, B).On the right forearm, the reversed PLM was284.54 mm in length. It arose from the humerus’ medialepicondyle by means of a 150.37-mm-long and7-mm-thick tendon (Fig. 1A). This tendon extended downto the forearm’s lower two thirds, its deep surfacein relation with the FDS muscle. The muscle then ex-tended distally via a muscular belly, with a length of119.17 mm and a maximum width of 18.4 mm at197.37 mm from its proximal insertion in the medialepicondyle. The muscle finally inserted into the pal-mar aponeurosis in the hand through a small, 15-mm-longand 5.4-mm-wide tendon. The distance between theright reversed PLM and the FCU muscle’s tendon was9.9 mm. These muscles came together at the pointwhere they both displayed their muscular belly. Theright reversed PLM’s muscular belly was located5.2 mm from the ulnar artery, 10 mm from the ulnarnerve, 12.3 mm from the FCR muscle’s tendon, and20 mm from the radial artery. The right reversed PLM’s mus-cular belly and distal tendon were laterally related tothe median nerve, which, at this point, showed a dia-meter of 4.47 mm. At the flexor retinaculum thesestructures were 5 mm apart (Fig. 2A).The left reversed PLM was 273.69 mm in length,arising from the humerus’ medial epicondyle asa 125.13-mm-long and 5.5-mm-wide tendon locatedsuperficially with respect to the FDS muscle (Fig. 1B).It then continued displaying a 148.56-mm-long mus-cular belly, which reached its maximum width (18 mm)at 238.69 mm from its proximal insertion into thehumerus’ medial epicondyle. These muscular fibrescontinued until inserted directly into the palmar apo-neurosis. At the flexor retinaculum, the left reversedPLM was located 10 mm medially from the FCR mus-cle, disposed at 8.6 mm medially from the radial ar-tery, 8 mm laterally from the FCU tendon, 4.5 mmlaterally from the ulnar nerve, and 2 mm laterally fromthe ulnar artery. At two thirds of the forearms, theulnar artery came into direct contact with the left re-versed PLMs’ muscular belly (Fig. 2B). During its prox-imal trajectory, the left reversed PLM was located me-dially with respect to the median nerve. However, onthe forearms’ distal third, the muscle came into directcontact with the PLM’s muscular belly, displayingmedian nerve compression and torsion. Proximal tothe compression site, the median nerve showed a di-ameter of 4.56 mm and, at the site of compression,exhibited a diameter of 2.78 mm, and toward the dis-tal region it recovered its original diameter (4.41 mm).Figure 1. Anatomical image of the right and left upper limbs. Thereversed palmaris longus muscles (PLM) on both forearms weredissected exposing the proximal and distal insertion; A. The rightreversed PLM with surrounding structures; B. The left reversedPLM with surrounding structures; PLMT — reversed palmarislongus muscle tendon; FDSM — flexor superficialis digitorummuscle; FCUM — flexor carpi ulnaris muscle; FCRMT — flexorcarpi radialis muscle tendon; BRM — brachioradialis muscle;MN — median nerve; RV — radial vessels; UV — ulnar vessels;ABBM — bicipital aponeurosis.54Folia Morphol., 2012, Vol. 71, No. 1DISCUSSIONThe PLM is extremely variable in both numberand shape [15]. The presence or absence of the PLMhas no effect on hand grip strength [13]. However,it has been shown that the thumb’s abductionstrength is larger in hands where the PLM can befound [4]. These observations are controversial asthey question the current idea that the PLM is re-dundant and that its main advantage arises whenused as material for grafts or tendon transplanta-tion to recover thumb movement [3].In our dissection, the reversed PLMs, both right andleft, showed a tendinous origin at the site of the me-dial epicondyle and a muscular insertion at the site ofthe palmar aponeurosis. These findings correlate withthe description in the literature regarding this type ofvariation [15]. According to Natsis et al. [7] the mus-cle exhibits a thin and wide tendon, which, in our case,showed to be 150.37 mm long and 7 mm wide on theright tendon, while showing to be 125.15 mm longand 5.5 mm wide on the left tendon. In both cases,the reversed PLM was located superficially in relationto the FSD muscle, displaying the required characteri-stics for it to be considered useful as a donor site.Many cases of reverse PLM have been described,either as an anatomical or surgical finding [1, 2, 5, 9,11, 12, 15]. However, the co-existence of this ano-maly on both limbs in the same individual is extremelyrare, and the existence of a bilateral reversed PLMhas only once been described in the specialised lite-rature, on a 21-year-old male patient. This study pointsout that the patient showed symptoms of temporalmedian nerve compression in both forearms, outsidethe carpal tunnel, and in the distal segment of theforearm, which was caused by the reversed PLM’shypertrophy. Resection of the PLM’s muscular bellyrelieved the symptoms immediately [5].Reimann et al. [10] studied reversed PLMs in 1600upper limbs, classifying their anatomical variations.Agenesis was found to be the most common (12.8%).All other PLM variations amounted to 9%. The exist-ence of two separate PLMs and variations in shapealso were included. After agenesis, variations in mus-cle form were the most common, summing up al-most 50% of cases previously mentioned and repre-senting 4.5% of the total cases. These variations makereference to the disposition of the muscular massalong the muscle, which may be found on its upperportion, in the middle, or even on its inferior extreme.Although the PLM’s muscular belly passes overthe flexor retinaculum, it may produce symptomsbecause of compression on the median nerve be-fore it becomes inserted in the carpal tunnel. Whenused excessively, this may cause a compartment syn-drome (effort-related compartment syndrome) [8].In the case of the reversed PLM, it is the antebra-chial fascia that creates a closed muscular compart-ment. As a result of this, compression is transferredto all adjacent structures, whereas the local hyper-trophy of the PLM’s muscular belly (due to excessiveuse) only worsens this condition [1, 2, 5, 7, 12, 15].The correlation between the presence of a re-versed PLM and carpal tunnel syndrome has beenconfirmed in the literature. The symptoms developedby patients include inflammation on the palmar sur-face of the wrist, reduced muscle strength in thehand, and pain and numbing in the area of distri-bution of the median nerve [7].Schuurman and van Gils [12] have reported the pres-ence of a unilateral reversed PLM as a plausible sourceof pressure in patients diagnosed with median nervecompression. In our report, the right reversed PLM wasFigure 2. A. Distal insertion of the right reversed palmaris lon-gus muscle (PLM); B. Distal insertion of the left reversed PLM;MN — median nerve; RV — radial vein; UN — ulnar nerve;UV — ulnar vessels; FDSM — flexor superficialis digitorummuscle; FCUMT — flexor carpi ulnaris muscle tendon;FCRMT — flexor carpi radialis muscle tendon.55G. Salgado et al., Bilateral reversed palmaris longus musclelocated laterally with respect to the median nerve. Thenerve showed no signs of compression. However, theleft reversed PLM was located medially with respect tothe median nerve, and on the distal third of the fore-arm it came in direct contact with the muscular belly,generating both compression and torsion on the medi-an nerve and reducing its diameter from 4.56 to2.78 mm. Distally, past the compression zone, it recoveredits diameter to 4.41 mm. Many studies have confirmedthat the presence of a reversed PLM can be a source ofcompression with the median nerve when enduringrepetitive work-related tasks [1, 2, 6, 7, 15]. In suchcases, surgical removal of the reversed muscle has beenused to relieve related symptoms [1, 2, 9, 12, 15].In recent studies, MRI has been used to evaluatethe cause of symptoms and oedemas in patients inwhom the diagnosis of a reversed PLM was prob-lematic [2, 12]. This may be explained because ofthe fact that the reversed PLM’s muscular belly showsthe same signs in the MRI as the rest of the musclesin the forearm but also by a lack of awareness ofthe existence of such anatomical variation [2].Considering the presence of these muscularanomalies, it seems reasonable to indicate a rou-tine ultrasound scan or MRI to study the PLM in pa-tients who express symptoms but cannot be clini-cally observed [8]. Therefore, the reversed PLM varia-tion must be considered not only while evaluatinga possible median nerve neuropathy but also whileevaluating an ulnar nerve neuropathy in the wrist,such as Guyon’s canal syndrome [9].The case previously described is both the secondreport describing a bilateral reversed PLM in the litera-ture and the first report describing it as an anatomicalfinding. Knowledge of this variation is useful for or-thopaedic surgeons when evaluating symptoms ofmedian or ulnar nerve compression, which tends toget worse during hand movements. Radiologistsshould also be aware of this variation, as its diagnosisis made difficult because of the large number of mus-cles in the forearm. Also, PLM variations are useful toboth plastic surgeons, which may use the tendon asa graft, and surgeons that work in that area, as the PLM’stendons act as an important landmark used as an an-atomical reference during surgical procedures.Lastly, finding these anatomical variations in ca-davers dissected with educational purposes at ourAnatomy Department poses great educational valueto our undergraduate medical students, who get toexperience first hand the human body’s immense vari-ability, ridding their minds of the fictitious and unrealarchetype shown in anatomical models, educationaltools of widespread use in many medical schools inour country today. Likewise, these observations areattractive to postgraduate students (subtends doingtheir internship in anaesthesia, traumatology, etc.),who, because of their high-level profession training,are able to appraise the implications of this anatomi-cal knowledge in their daily clinical work. Also, it al-lows us to contribute to the knowledge of anatomicalvitiations and their medical and clinical implications.REFERENCES1. Bencteux P, Simonet J, el Ayoubi L, Renard M, Atti-gnon I, Dacher JN, Thiebot J (2001) Symptomatic pal-maris longus muscle variation with MRI and surgicalcorrelation: report of a single case. Surg Radiol Anat,23: 273–275.2. Depuydt KH, Schuurman AH, Kon M (1998) Reversedpalmaris longus muscle causing effort-related mediannerve compression. J Hand Surg Br, 23: 117–119.3. Erić M, Koprivčić I, Vučinić N, Radić R, Krivokuća D,Lekšan I, Selthofer R (2010) Prevalence of the palmarislongus in relation to the hand dominance. Surg RadiolAnat, 33: 481–484.4. Gangata H, Ndou R, Louw G (2010) The contributionof the palmaris longus muscle to the strength of thumbabduction. Clin Anat, 23: 431–436.5. Giunta R, Brunner U, Wilhelm K (1993) Bilateral reversedpalmaris longus muscle: a rare cause of peripheral me-dian nerve compression syndrome. Case report. Un-fallchirurg, 96: 538–540.6. Güler MM, Celiköz B (1998) Anomalous palmaris lon-gus muscle causing carpal tunnel-like syndrome. ArchOrthop Trauma Surg, 117: 296–297.7. Natsis K, Levva S, Totlis T, Anastasopoulos N, Paraskevas G(2007) Three-headed reversed palmaris longus muscleand its clinical significance. Ann Anat, 189: 97–101.8. Rawat JS, John B (2003) Reverse palmaris longus mus-cle: a case report. Indian J Orthop, 37: 13.9. Regan PJ, Roberts JO, Bailey BN (1988) Ulnar nerve com-pression caused by a reserved palmaris longus muscle.J Hand Surg Br, 13: 406–407.10. Reimann AF, Daseler EH, Anson BJ, Beaton LE (1944)The palmaris longus muscle and tendon. A study of1600 extremities. Anat Rec, 89: 495–505.11. Schlafly B, Lister G (1987) Median nerve compressionsecondary to bifid reversed palmaris longus. J Hand SurgAm, 12: 371–373.12. Schuurman AH, van Gils AP (2000) Reversed palmarislongus muscle on MRI: report of four cases. Eur Radiol,10: 1242–1244.13. Sebastin SJ, Lim AY, Bee WH, Wong TC, Methil BV(2005) Does the absence of the palmaris longus affectgrip and pinch strength? J Hand Surg Br, 30: 406–408.14. Still JM, Kleinert HE (1973) Anomalous muscles andnerve entrapment in the wrist and hand. Plast Recon-str Surg, 52: 394–400.15. Yildiz M, Sener M, Aynaci O (2000) Three-headed re-versed palmaris longus muscle: a case report and re-view of the literature. Surg Radiol Anat, 22: 217–219.

Bilateral reversed palmaris longus muscle: a rare anatomical variation

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Bilateral reversed palmaris longus muscle: a rare anatomical variation

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