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Year : 2021  |  Volume : 70  |  Issue : 2  |  Page : 116-118

A unilateral anomalous muscle with an uncommon nerve supply interconnecting the biceps femoris and the gastrocnemius

School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, Republic of South Africa

Date of Submission25-Jun-2019
Date of Acceptance22-May-2020
Date of Web Publication30-Jun-2021

Correspondence Address:
Dr. Oladiran Ibukunolu Olateju
School of Anatomical Sciences, Faculty of Health Sciences, University of the Witwatersrand, 7 York Road, Parktown 2193, Johannesburg
Republic of South Africa
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/JASI.JASI_85_19

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This case study describes the morphology and embryology and hypothesizes the muscle action based on the morphology of an anomalous muscle that extends from the long head of the biceps femoris to the medial head of the gastrocnemius muscles. It has an uncommon nerve supply via the medial sural cutaneous nerve which is mainly sensory in humans. This variation is different from other similar variations involving the gastrocnemius and biceps femoris muscles. The case report will be of benefit to diagnosis, clinical training, and surgical procedures as well as contribute to knowledge on the type of nerve fiber carried by the medial sural cutaneous nerve or its components.

Keywords: Anomalous muscle, biceps femoris, gastrocnemius, medial sural cutaneous nerve, tensor fascia suralis, third head of gastrocnemius

How to cite this article:
Olateju OI. A unilateral anomalous muscle with an uncommon nerve supply interconnecting the biceps femoris and the gastrocnemius. J Anat Soc India 2021;70:116-8

How to cite this URL:
Olateju OI. A unilateral anomalous muscle with an uncommon nerve supply interconnecting the biceps femoris and the gastrocnemius. J Anat Soc India [serial online] 2021 [cited 2022 Nov 27];70:116-8. Available from: https://www.jasi.org.in/text.asp?2021/70/2/116/320286

  Introduction Top

The most common variation of the gastrocnemius is the presence of an additional head that inserts into the popliteal fossa. This is called the third or accessory head of the gastrocnemius muscle.[1],[2],[3],[4] This abnormally placed muscle, with variable proximities to the popliteal artery or vein, may compress the popliteal vessels therefore causing problems that may require surgical interventions.[2],[3],[4],[5],[6] Another variation that often involves one or two hamstring (biceps femoris or semitendinosus) muscles is tensor fascia suralis or ischioaponeuroticus. This muscle usually arises from either or both hamstring muscles and then inserts by blending with the fascia of the leg.[7],[8] The present case study describes the morphology and embryology and hypothesizes the function of the anomalous muscle based on its morphology and location. This muscle variation is rare and has an uncommon nerve supply via the medial sural cutaneous nerve.

  Case Report Top

A 71-year-old male cadaver (from bequests/donation process) of South African of European ancestry was used during a routine dissection for the undergraduate medical students, permitted under the Human Ethics number: W-CJ-140604-1. After removing the skin and the deep fascia (fascia lata) to reveal the popliteal contents, a nerve-like structure initially thought to be a tibial nerve or its variant was observed in the fossa on the left leg. By tracing the tendon proximally and distally, the whole length of the anomalous muscle [[Figure 1]a – indicated by arrows] measuring approximately 43 cm in length became obvious. The anomalous muscle extended from the media side of the long head of bicep femoris to the medial head of the gastrocnemius muscles. For morphological description, the anomalous muscle [Figure 1]a, [Figure 1]b, [Figure 1]c had three observable and distinguishable parts – proximal, intermediate, and distal.
Figure 1: Photographs showing (a) the extent of the anomalous muscle (indicated by arrows) and its intermediate part (indicated by white arrows), (b) the proximal part with its muscle belly (indicated by no color – filled arrows) and (c) the distal part with its muscle belly ([c] – indicated by black arrows) on the posterior aspect of the lower limb. Photograph (d) shows a small muscular branch (11) from the medial sural cutaneous nerve (9) supplying the anomalous muscle. 1: Semitendinosus, 2: Long head of biceps femoris, 3: Short head of the biceps femoris, 4: Tibial nerve, 5: Common fibular nerve, 6: Lateral head of the gastrocnemius, 7: Lateral sural cutaneous nerve, 8: Small saphenous vein, 9: Medial sural cutaneous nerve, 10: Medial head of the gastrocnemius, 11: Small muscular branch from the medial sural cutaneous nerve, M: Medial, D: Distal

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The proximal part, presumably the muscle origin about 17 cm from the ischial tuberosity [[Figure 1]b – indicated by no-colour filled arrows], was fleshy, flattened mediolaterally and had a muscle belly that was about 2 cm wide and 16 cm long. It attached to the bicep femoris via a tendinous aponeurosis and tapered distally to become tendinous (intermediate part) at about 33 cm from the ischial tuberosity. This part was supplied through intramuscular branches of the sciatic nerve innervating the bicep femoris.

The intermediate part [[Figure 1]a – indicated by white arrows] was tendinous and laid in line with the tibial nerve within the popliteal fossa. Its tendon was thick and strong, measured about 12 cm long. This tendon connected the two ends of the anomalous muscle (i.e. the two bellies). Distally, it deviated slightly to the medial side to attach to the muscle belly of the distal part (at about 45 cm from the ischial tuberosity).

The distal part had a muscle belly and flattened anteroposteriorly. It measured about 1.8 cm wide and 15 cm long [[Figure 1]c – indicated by black arrows]. It rested entirely on the medial head of the gastrocnemius with the medial sural cutaneous nerve and the small saphenous vein medial to it. Its fibers blended with the superficial fibers of the medial head of the gastrocnemius muscle (at about 60 cm from the ischial tuberosity) with no visible tendinous aponeurosis. This part was presumed to be the insertion of the anomalous muscle. On careful examination, this part received a small muscular branch from the medial sural cutaneous nerve [Figure 1]d which was positioned underneath the muscle belly.

  Discussion Top

Several variations involving human skeletal muscles are common. These variations are often due to abnormalities during the embryonic development of skeletal muscles. All progenitor cells of the limb skeletal muscles are derived from the somites[9] which were initially formed after a series of migration and de-epithelization aided by several transcription factors.[10] Thereafter, the muscle masses undergo sequence of orientation, mitosis, lengthening, and delamination to form the individual muscles of the limbs.[9] It is thus believed that a failure in the sequence of events (for example incomplete delamination or disorientation) would result into variations sometimes seen in humans.[9],[10]

Most variations do not always present with severe clinical problems; thus, they usually remain unnoticed. Some however cause serious problems to structures within the proximity of the muscle variation that may require surgical intervention.[2] A good example is the third head of the gastrocnemius muscle which may compress the popliteal neurovasculatures.[1],[2],[3],[4],[6] Morphologically, it is improbable that the intermediate tendon (or its other parts) of the present variation would have caused any clinical problems in the subject while he was alive despite its close proximity to the tibial nerve.

The tensor fascia suralis has no associated clinical problem. It could arise from either the semitendinosus or the biceps femoris or from both but ends as a tendon that blends with the fascia of the leg.[7],[8] A similar variation was reported by Kumar and Bhagwat[11] which consisted a proximolateral (attachment on the medial side of the long head of biceps femoris), a proximomedial (attachment on the medial side of the semitendinosus), a middle (fleshy and tapered distally to form a somewhat “W” shaped intersection), and a distal part (fleshy and inserted between the two heads of gastrocnemius muscle). Another anomalous muscle arising from the medial side of the long head of the biceps femoris but fusing only with the semitendinosus has also been described.[12] A variation similar to the latter was also reported by Somayaji et al.,[13] but the muscle inserted superficially into the tendocalcaneus.

The present case differs morphologically from other variations in that the anomalous muscle only attached to the long head of the biceps femoris before blending superficially with the medial head of the gastrocnemius where it received a muscular branch from the medial sural cutaneous nerve – a striking feature of this anomalous muscle. The medial sural cutaneous nerve arises from the tibial nerve and it is the main trunk that forms the sural nerve. In addition, the sural nerve formation is highly variable; thus, it is often called a sural nerve complex.[14] Sural nerve transmits sensation from the skin on the posterolateral area of the lower third of the leg. However, the sural nerve may also carry motor fibers which are considered rare in humans.[14],[15] This uncommon innervation of a muscle variation involving the gastrocnemius and biceps femoris has not been reported in the literature. This is of clinical relevance in that surgeons need to investigate the complexity of sural nerve formation and the type of fibers (sensory or motor) it conveys before harvesting the nerve as an autograft. The sural, lateral, or medial sural cutaneous nerve could be harvested depending on factors such as the length of graft required and the complex nature of sural nerve formation.[15] In this scenario, for example, it would be the medial sural cutaneous nerve that would be spared. Other clinical relevancies are in research on nerve conduction studies as well as in nerve biopsy for diagnosing neuropathies of unclear underlying cause after conventional diagnostic assessments.[16]

It is reasonable to think that muscle variants may have no specific function (i.e. redundant muscle slip) because muscle variations often occur by accidents during development. Morphologically, this anomalous muscle could be said to have an origin (proximal end) and an insertion (distal end). The muscle belly thickness and the strong intermediate tendon signaled that this muscle when it contracts and acts together with other hamstrings would play a synergistic role during knee flexion. It must be emphasized that documenting the exact functions of muscle variations in cadavers may remain difficult, but their morphological features may provide cues for hypothesizing their action. Furthermore, the rarity of a variation or when present could be unnoticed due to no clinical problem that may warrant medical investigation.

  Conclusion Top

This anomalous muscle is rare, and its uncommon innervation further shows that the medial sural cutaneous nerve carries motor fibers which may innervate an anomalous muscle when present. Awareness of such variation or its innervation will be of benefit during nerve conduction studies, diagnosis, and surgeries. It is also hypothesized that the anomalous muscle may have acted as a synergist during knee flexion.


The author is grateful to the School of Anatomical Sciences, University of The Witwatersrand, for granting access to the human collections. This case report would not be possible without the aid of those who donated their bodies toward the advancement of medical science.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Liu PT, Moyer AC, Huettl EA, Fowl RJ, Stone WM. Popliteal vascular entrapment syndrome caused by a rare anomalous slip of the lateral head of the gastrocnemius muscle. Skeletal Radiol 2005;34:359-63.  Back to cited text no. 1
Dave MR, Yagain VK, Anadkat S. Unilateral third/accessory head of the gastrocnemius muscle: A case report. Int J Morphol 2012;30:1061-64.  Back to cited text no. 2
Molinaro V, Pagliasso E, Varetto G, Castagno C, Gibello L, Zandrino F, et al. Popliteal artery entrapment syndrome in a young girl: Case report of a rare finding. Ann Vasc Surg 2012;26:572.e5-9.  Back to cited text no. 3
Iwai T, Sato S, Yamada T, Muraoka Y, Sakurazawa K, Kinoshita H, et al. Popliteal vein entrapment caused by the third head of the gastrocnemius muscle. Br J Surg 1987;74:1006-8.  Back to cited text no. 4
Bergman RA, Walker CW, el-Khour GY. The third head of gastrocnemius in CT images. Ann Anat 1995;177:291-4.  Back to cited text no. 5
Stager A, Clement D. Popliteal artery entrapment syndrome. Sports Med 1999;28:61-70.  Back to cited text no. 6
Tubbs RS, Salter EG, Oakes WJ. Dissection of a rare accessory muscle of the leg: The tensor fasciae suralis muscle. Clin Anat 2006;19:571-2.  Back to cited text no. 7
Bale LS, Herrin SO. Bilateral tensor fasciae suralis muscles in a cadaver with unilateral accessory flexor digitorum longus muscle. Case Rep Med 2017;2017:1864272.  Back to cited text no. 8
Buckingham M, Bajard L, Chang T, Daubas P, Hadchouel J, Meilhac S, et al. The formation of skeletal muscle: From somite to limb. J Anat 2003;202:59-68.  Back to cited text no. 9
Straus WL, Temkin O. Vesalius and the problem of variability. Bull Hist Med1943;14:609.  Back to cited text no. 10
Kumar GR, Bhagwat SS. An anomalous muscle in the region of the popliteal fossa: A case report. J AnatSoc India 2006;55:65-8.  Back to cited text no. 11
Chakravarthi K. Unusual unilateral multiple muscular variations of back of thigh. Ann Med Health Sci Res 2013;3:S1-2.  Back to cited text no. 12
Somayaji SN, Vincent R, Bairy KL. An anomalous muscle in the region of the popliteal fossa: Case report. J Anat 1998;192(Pt 2):307-8.  Back to cited text no. 13
Kavyashree AN, Subhash LP, Asha KR, Bindu Rani MK. Anatomical variations in formation of sural nerve in adult Indian cadavers. J Clin Diagn Res 2013;7:1838-41.  Back to cited text no. 14
Seema SR. Study of sural nerve complex in human cadavers. ISRN Anat 2013;2013:827276.  Back to cited text no. 15
Bevilacqua NJ, Rogers LC, Malik RA, Armstrong DG. Technique of the sural nerve biopsy. J Foot Ankle Surg 2007;46:139-42.  Back to cited text no. 16


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