In the Dissection Team of the Second Chair of Anatomy at the School of Medicine
of the University of Buenos Aires, Argentina, during the routine dissection
of 78 cadavers (corresponding to 156 supraclavicular fossae),10% formalin fixed,
we found the supraclavicularis proprius muscle over the lower part of the left
supraclavicular fossa in an adult Caucasian male cadaver. We described this
rare muscular anomaly, the likelihood of finding this muscle, and its participation
in supraclavicular nerve entrapment syndrome

Medan, C.

Ottone, N.E.

English

Via Medica Journals

Folia Morphol. Vol. 68, No. 1, pp. 55–57Copyright © 2009 Via MedicaISSN 0015–5659www.fm.viamedica.plC A S E   R E P O R T55Address for correspondence: N.E. Ottone, Melincué 5308, Postal Code: 1408, Ciudad Autónoma de Buenos Aires, Argentina,e-mail: nicolasottone@gmail.comA rare muscle anomaly: the supraclavicularisproprius muscleN.E. Ottone, C. MedanDissection Team (Dr V.H. Bertone), Second Chair of Anatomy, School of Medicine,University of Buenos Aires, Argentina[Received 17 September 2008; Accepted 15 November 2008]In the Dissection Team of the Second Chair of Anatomy at the School of Med-icine of the University of Buenos Aires, Argentina, during the routine dissectionof 78 cadavers (corresponding to 156 supraclavicular fossae),10% formalin fixed,we found the supraclavicularis proprius muscle over the lower part of the leftsupraclavicular fossa in an adult Caucasian male cadaver. We described thisrare muscular anomaly, the likelihood of finding this muscle, and its participa-tion in supraclavicular nerve entrapment syndrome. (Folia Morphol 2009;68, 1: 55–57)Key words: supraclavicularis proprius muscle, supraclavicular fossa,supraclavicular nerve entrapment syndromeINTRODUCTIONThe supraclavicularis proprius muscle is an ab-normal muscle that may be found in the supraclav-icular fossa. It consists of an anterior tendon insert-ing into the sternal aspect of the clavicle, lateral tothe clavicular insertion of the sternocleidomastoi-deus muscle, and a posterior muscular portion en-tering the lateral aspect of the clavicle, medial tothe acromioclavicular joint. This anatomic variantwas first described by Gruber (1865) [9], who calledit the tensor fascia colli, on account of his findingthat its contraction made tense the superficial layerof the cervical fascia that contained it. Since thena few authors have described this abnormal mus-cle: Macalister (1875) [19], Bardeleben (1876) [1],Knott (1880) [16], Dubar (1880) [6], Le Double(1897) [18], Laidlaw (1902) [17], Eisler (1912) [7],and Stadler (1930) [24]. However, none of themprovided any information on its frequency of occur-rence. Only Bergman et al. [2] reported that clavicu-lar supernumerary muscles are numerous but un-common. With respect to its embryological origin,Mori [21] indicates that the trapezius and sterno-cleidomastoideus muscles develop from the bran-chial musculature, so it is presumed that the supra-clavicularis proprius muscle evolved from the stern-ocleidomastoideus and trapezius muscles, of whichit represents an abnormal persistence [2, 7, 14, 17,24, 25]. Here we describe our finding of a supra-clavicularis proprius muscle, its frequency of occur-rence according to our experience, and its clinicalsignificance.CASE REPORTIn the Dissection Team of the Second Chair ofAnatomy, at the School of Medicine of the Universi-ty of Buenos Aires, during the routine dissection of78 cadavers (10% formalin-fixed), we found thisabnormal muscle over the lower part of the left su-praclavicular fossa in an adult Caucasian male ca-daver (Fig. 1). Measuring 8.3 cm long, the musclewas enclosed between the superficial and deep lay-ers of the fascia colli overlying the clavicle with aninferiorly concave curvature. It inserted into the pos-terior border at the lateral end of the clavicle, 4.2 cmfrom the acromion process, between the acromio-56Folia Morphol., 2009, Vol. 68, No. 1clavicular insertion fibres of the trapezius muscle.It exhibited a tendinous medial insertion at the levelof the anterior border of the clavicle, 3.5 cm from thesternoclavicular joint, lateral to the sternocleidomas-toideus muscle. The supraclavicular nerve, before pass-ing underneath this abnormal muscle and through thespace it formed with the clavicle, provided a small twigto the dorsal aspect of the muscle, which would beresponsible for its innervation. Therefore, as previous-ly suggested by Laidlaw [17], Eisler [7], Stadler [24]and Havet et al. [11], innervation of this muscle wouldbe supplied by C3 and C4 ventral rami.DISCUSSIONTo our knowledge, data on the frequency of oc-currence of this abnormal muscle is lacking. OnlyBergman et al. [2] reported that clavicular supernu-merary muscles are numerous but uncommon. Inour experience, the frequency of occurrence of thesupraclavicularis proprius muscle would be 0.64%,based on a total of 156 supraclavicular fossae dis-sected in 78 Caucasian adult cadavers.Historically, this muscle variant has beentermed variably. Gruber called it praeclavicularissubcutaneous and, because of its action, tensorfascia colli. Later, Testut [25] developed a classifi-cation of clavicular supernumerary muscles, andincluded this variant as belonging to the group of“musculus cleido-aponévrotique ascendant, ten-sour de l´aponévrose sous-claviculaire.” Finally, it wasLaidlaw [17] who, in 1912, first employed the cur-rently used term, supraclavicularis proprius muscle.Hyrtl [12] and Bryce [3] described a “sterno-clav-icularis muscle”, which had an anterior tendon ex-tending medially and anteriorly to the sternum.Haller [10] established that the frequency of occur-rence of this rare muscle anomaly is in 1 in 30 bod-ies. Jinguji and Takisawa [14] described yet anotherform of this muscle in a female cadaver, the supra-clavicularis singularis, extending from the ventralsurface of the sternal manubrium to the clavicularinsertion of the sternocleidomastoideus muscle, andlocated posteriorly to this muscle. To our mind, noneof these muscles conforms to the description of thesupraclavicularis proprius; instead, these muscleanomalies represent other clavicular supernumerarymuscles, and show the high muscle variability thatmay be found in this region, as already observed byBergman et al. [2].Clinically, supraclavicular nerve entrapment andcompression have been attributed to intraclavicularosseous canals, clavicle fractures, or trapezius mus-cle expansions [4, 5, 8, 13, 15, 20, 22, 23, 26, 27].Gelberman et al. [8] were the first to describe supr-aclavicular nerve entrapment and compression asa syndrome, calling it supraclavicular nerve entrap-ment syndrome, but never has the supraclavicularisproprius muscle been mentioned as a cause of sucha syndrome. We can presume that, due to the closerelationship that exists between the supraclavicu-laris proprius muscle, the clavicle, and the supra-clavicular nerve [7, 17], when in action, the musclemay compress the supraclavicular nerve against theclavicle, which would be a potential cause of supra-clavicular nerve entrapment syndrome, causingshoulder pain.We conclude that comprehensive knowledge ofnormal and abnormal anatomy is essential to per-form any kind of clinical and surgical procedures witha high degree of confidence and precision. This find-ing has shown that although the supraclavicularisproprius muscle is a rare anatomical variant, knowledgeFigure 1. The supraclavicularis proprius muscle over the lower portion of the leftsupraclavicular fossa.57N.E. Ottone, C. Medan, A rare muscle anomaly: the supraclavicularis proprius muscleregarding its possible occurrence may provide a hy-pothesis as to its potential involvement in supra-clavicular nerve entrapment syndrome.ACKNOWLEDGEMENTSWe would like to thank Prof. Dr. Vicente HugoBertone (Dissection Team) for his useful contribu-tion to the proofreading of this article, Prof. Dr.Homero Bianchi (Anatomy Department, School ofMedicine, University of Buenos Aires) for his perma-nent support, Prof. Dr. Lachezar Surchev (Depart-ment of Anatomy, Histology and Embryology, Medi-cal University Sofia, Bulgaria) for aiding us to findimportant articles, and Dr. Youichi Jinguji (Depart-ment of Anatomy, Gunma Prefectural College ofHealth Sciences, Maebashi, Japan) for sending ushis work.REFERENCES1. 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A rare muscle anomaly: the supraclavicularis proprius muscle

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A rare muscle anomaly: the supraclavicularis proprius muscle

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