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Soleus


Original Editor ­ Aarti Sareen

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Introduction

Located in superficial posterior compartment of the leg Soleus is a powerful lower limb muscle, which is situated deep to the gastronemius muscle[1]. Together with gastronemius and plantaris, it forms the calf muscle or triceps surae. It runs from back of the knee to the ankle and is multipennate.

The soleus has the greatest physiological cross sectional area (CSA) of the calf muscles and is thought to provide up to 80% of triceps surae force[2].

Muscle Physiological CSA (cm²) %
Soleus 230 71
Medial Gastrocnemius 68 22
Lateral Gastrocnemius 28 7

Anatomy

Origin

  • Upper 1/3 of the shaft of the fibula and Posterior surface of the head
  • Middle 1/3 of the medial border of the tibia, tendinous arch between tibia and fibula[3]

Insertion

  • Posterior surface of the calcaneus along the Achilles tendon[3]

Action

  • Plantar flexion of the foot at the ankle
  • Soleus muscle stabilizes the tibia on the calcaneus limits forward sway
  • When standing, the calcaneus becomes the fixed origin of the muscle likeReversed origin insertion action[3]

Nerve supply

Tibial nerve, L4, L5, S1 , S2[3]

No sensory supply to the intramuscular aponeurosis.

Synergists

Gastrocnemius, Plantaris, Tibialis posterior, Flexor Hallucis Longus and Flexor Digitorum Longus, Peroneus longus and Brevis[3].

Antagonists

Tibialis anterior

Blood supply

  • The soleus muscle receives its blood supply from peroneal artery proximally and the posterior tibial artery distally
  • Muscle has a mixed circulatory network
  • The proximal part of muscle get its supply from popliteal, posterior tibial & peroneal vascular pedicles, whereas, distal lateral belly of muscle receives blood from peroneal pedicle, and distal medial belly from segmental posterior tibial pedicles
  • When the distal pedicles from the posterior tibial artery are tied off, while maintaining the proximal pedicles from the posterior tibial and peroneal arteries, the muscle can be shifted medially or laterally to address deficiencies in the middle third of the leg
  • Proximal vasculature emerges directly from the popliteal vessels and can sustain perfusion to all but the distal 4 to 5 cm of the muscle
  • Intramuscularly, vasculature of the soleus bifurcates into a bipenniform segmental pattern
  • With this circulatory pattern, either half of the soleus muscle can be used, leaving a functional hemisoleus muscle intact[4]

Function

Soleus has two major functions:

  • To act as skeletal muscle:
    • Along with other calf muscles it is powerful plantarflexor[1] and has a major contribution in running, walking and dancing.
    • It is also a major postural muscle designed to stop the body from falling forwards at the ankle during stance.[1]
    • In the seated calf raise (knees flexed approximately 90º), the gastrocnemius is virtually inactive while the load is borne almost entirely by the soleus, movement as termed the soleus push up.
    • In moderate force, the soleus is preferentially activated in the concentric phase, whereas the gastrocnemius is preferentially activated in the eccentric phase [5].
    • Human soleus muscle tissue consists predominantly of slow twitch fibers, though the composition can range between 60 and 100% slow fibers.[6][7][8].
  • To act as muscle pump:
    • The soleal pump assists with venous return from the periphery to the heart when upright as the venous circulatory system passes through the muscle tissue[9].

Palpation

When palpating the Soleus, plantarflex the ankle with the knee flexed to 90 degrees to ensure that gastrocnemius remains relaxed.  The lateral and medial aspects of the muscle can then be palpated from the lateral and medial sides of the Achilles tendon. The muscle is palpable for most of the distance from distal to proximal though the proximal attachments will become more difficult to palpate if the heads of gastrocnemius are large.

Accessory soleus muscle (ASM)

It is present in 0.7 to 5.5% of humans.[10] It is usually observed during the second or third decade of life and is more commonly seen in females than males at a ratio of 2:1. It is mostly unilateral.[11][10][12][13][14]. This supernumerary muscle is located under the gastrocnemius muscle, in the posterior upper third of the fibula, in the oblique soleus line, between the fibular head and the posterior part of the tibia. From its origin, the ASM runs anteriorly and medially until it reaches the Achilles tendon.[15]

                        

Depending upon its insertion it is of 5 types, or in other words it can origininate from 5 sites

  • Achilles tendon
  • Upper calcaneus region
  • Insertion in the upper calcaneus,
  • Medial calcaneus region,
  • Medial part of the calcaneus

Sometimes it is impossible to precisely identify the ASM origin and insertion, since the MRI fails to show details, depending on the slices[15]. It may cause pain on exercise. One may suspect a soft-tissue tumor, such as lipoma, hemangioma, and even sarcoma, but the anomalous muscle has a typical appearance on plain radiographs, and the appearance on computed tomography is diagnostic. If the patient is asymptomatic, no therapy is required, but if pain or other discomfort is provoked by exercise, exploration with fasciotomy or excision of the accessory muscle is recommended, as was done in six of our eleven patients who were seen between 1968 and 1985[11].

Pathology

Strain/Rupture

A muscle strain occurs when muscle fibers are damaged by the loads placed on them by activity. A gradual onset of pain is commonly reported during soleus strain and often with no specific mechanism of injury (MOI). This may be due to the limited sensory innervation to the intramuscular aponeurosis.  In cases where a specific MOI is identified, steady-state running appears to be the commonest cause of injury[16].

Symptoms:

  • Pain with active or resisted plantar flexion
  • Pain during walking, running, jumping or hopping
  • Tenderness on palpation of the injury site


Investigations:

Diagnostic ultrasound or MRI can be advantageous to confirm an injury diagnosis and ensure that injuries accurately assessed as full ruptures can be overlooked with clinical exam on occasion. [17]

Further information about soleus and calf strains is available here

References

  1. ↑ 1.0 1.1 1.2 Henry Gray (1825–1861). Anatomy of the Human Body. 1918. 8c. The Muscles and Fasciæ of the Leg
  2. ↑ Fukunaga T, Roy RR, Shellock FG, Hodgson JA, Day MK, Lee PL, et al. Physiological cross-sectional area of human leg muscles based on magnetic resonance imaging. J Orthop Res. 1992;10(6):928–34.
  3. ↑ 3.0 3.1 3.2 3.3 3.4 Duke Orthopaedics, Wheeless Textbook of Orthopaedics. Muscles Tendons, Soleus.
  4. ↑ Duke Orthopaedics, Wheeless Textbook of Orthopaedics. Bones, Tibia and Fibula, Vascular Supply of the Soleus.
  5. ↑ Nardone A, Romanò C, Schieppati M. Selective recruitment of high-threshold human motor units during voluntary isotonic lengthening of active muscles. J Physiol. 1989;409(1):451–71.
  6. ↑ Ariano MA, Armstrong RB, Edgerton VR. Hindlimb muscle fiber populations of five mammals. J Histochem Cytochem. 1973;21(1):51–5.
  7. ↑ Burke RE, Levine DN, Salcman M, Tsairis P. Motor units in cat soleus muscle: physiological, histochemical and morphological characteristics. J Physiol. 1974;238(3):503–14.
  8. ↑ Gollnick PD, Sjödin B, Karlsson J, Jansson E, Saltin B. Human soleus muscle: a comparison of fiber composition and enzyme activities with other leg muscles. Pflugers Arch. 1974;348(3):247–55.
  9. ↑ Vd Ashish A Bidkar, Dr. Sabir S. Mujawar, Dr. Raghavendra Nadargi, Study Of “Soleus Muscle’’ In Human Anatomy And Its Importance -A Literature Review, 2023 IJCRT, Volume 11, Issue 5 May 2023.
  10. ↑ 10.0 10.1 Salomão O, Carvalho Junior AE, Fernandes TD, Romano D, Adachi PP, Sampaio Neto R. Músculo solear acessório: aspectos clínicos e achados cirúrgicos.(The presence of accessory soleus muscle in humans) Rev Bras Ortop. 1994;29(4):251-5.
  11. ↑ 11.0 11.1 Romanus B, Lindahl S, Sterner B. Accessory soleus muscle. A clinical and radiographic presentation of eleven cases. J Bone Joint Surg Am. 1986; 68(5):731-4.
  12. ↑ Leswick DA, Chow V, Stoneham GW. Resident's corner. Can Assoc Radiol J. 2003;54(5):313-5.
  13. ↑ Featherstone T. MRI diagnosis of accessory soleus muscle strain. Br J Sports Med. 1995;29(4):277-8.
  14. ↑ Doda N, Peh WC, Chawla A. Symptomatic accessory soleus muscle: diagnosis and follow-up on magnetic resonance imaging. Br J Radiol. 2006;79(946):e129-32.
  15. ↑ 15.0 15.1 Del Nero FB, Ruiz CR, Aliaga Junior R. The presence of accessory soleous muscle in humans. Einstein (Sao Paulo). 2012;10(1):79–81.
  16. ↑ Pull MR, Ranson C. Eccentric muscle actions: Implications for injury prevention and rehabilitation. Physical Therapy in Sport. 2007 May 1;8(2):88-97.
  17. ↑ urtehave_com. Rupture of the soleus muscle - Sportnetdoc [Internet]. Sportnetdoc.com. 2011 [cited 2013 Aug 31]. Available from: http://sportnetdoc.com/foot-achilles/rupture-of-the-soleus-muscle
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