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Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: G: Gastrocnemius and Soleus

Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: G

Gastrocnemius and Soleus

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD

Peer Review Status: Internally Peer Reviewed

In view of its phylogenetic history and its development in humans, the gastrocnemius has been considered a muscle of the fibular side of the leg. This may also be true of the lateral head of the soleus. The soleus appears first in lower mammals and may be a derivative of the lateral head of the gastrocnemius. It has been suggested that the medial head of gastrocnemius is medial extension from the fibular head.

The gastrocnemius is frequently joined by a separate fascicle or head known as the third head of gastrocnemius. It arises from some part of the popliteal surface of the femur. Caput tertium may also arise from the linea aspera, long head of biceps femoris, lateral epicondyle, knee joint capsule, midfibula, and the crural fascia. The third head may "split" and arise from more than one location or divide near its termination to join both heads of gastrocnemius. The third head may or may not cross popliteal neurovascular structures or some portions of the neurovascular component before insertion into one head, or the other, of gastrocnemius or its tendon. A third head joining the medial head of gastrocnemius is most commonly cited as causing clinical problems; the lateral head may also be involved.The conditions of intermittent claudication, arterial stasis and aneurysm, venous stasis, and impaired nerve function must have had a long undescribed clinical history before being discovered by Hamming. The third head is the most common variation of the gastrocnemius muscle and it has been studied extensively over a period of almost 200 years. Kelch (1813) is generally cited as the first to report the third head. The third head commonly joins the medial head of gastrocnemius and the third head, regardless of which head of gastrocnemius it joins, it has an overall frequency of 2.9 to 5.5%. Mori reported it present in 2.8% of his cases. The third head may be a potential problem for structures in the popliteal fossa as illustrated by Frey in 1919 and reproduced here. It is remarkable that the first clinical report was not published until 1959 (Hamming). There is no evidence from the literature that this is a familial variation but this needs further study.The plantaris muscle itself can be the third head. The plantaris may become the third head and may join gastrocnemius at the point where the medial and lateral heads separate, or may become continuous with the fascia beneath the muscle. It has also been seen passing between the popliteal artery and nerve.

Absence of the lateral head of gastrocnemius and its reduction to a fibrous cord has been reported.In some cases the two heads of gastrocnemius may be unjoined until their insertion onto the calcaneus and with separation from soleus. The absence of the tibial head of soleus has been reported. An accessory muscular slip (soleus accessorius) may arise from the soleal line with the soleus or be detached from the muscle distally. It lies between the soleus tendo achillis (externally or laterally) and flexor hallucis longus (internally or medially). It ends on the tendo achillis, or it may have a separate attachment on the medial surface of the calcaneus or tibial collateral ligament of the ankle.

Additional slips are

  1. tensor fasciae plantaris, which inserts into the plantar fascia or quadratus plantae, and
  2. peroneotibialis, which is a tensor of the tendinous arch of the soleus arising from the posterior aspect of the medial surface of the upper tibia and inserting into the tendinous arch (arcus tendineus) of soleus.

Peroneotibialis was found in 128 of 680 limbs; it usually occurs bilaterally, but, when unilateral, is more frequently found in the right limb. Either or both heads of gastrocnemius may be doubled, the lateral head may be absent.

Soleus may be doubled or absent.

Macalister reported the variations of gastrocnemius as follows;

  1. Gastrocnemius may have a sesamoid bone in its medial head;
  2. Or in its lateral head-this more common;
  3. Or the two heads are separable further down than usual;
  4. Or their tendon is perfectly separate from that of the soleus for a few inches (1 inch = 2.54 cm.);
  5. The lateral head may have a few lower fibers attached to the external lateral ligament (ligamentum calcaneofibulare, ligamentum talofibulare anterius, and ligamentum talofibulare posterius);
  6. Or to the posterior ligament of Winslow ( ligamentum collaterale fibulare);
  7. A third head may be found from the middle of the popliteal triangle of the femur, and with a second slip from the posterior ligament of Winslow (ligamentum collaterale fibulare);
  8. Or it may arise from the line leading from the medial condyle to the linea aspera, an inch (2.54 cm) above the medial head-this ended in a short tendon, which crossed the popliteal nerve, and inserted into the convergence of the two heads;
  9. It may arise from a tendinous arch from the same ridge, higher up., which extends over the femoral vessels;
  10. Or from the medial border of the long head of the biceps, forming a bicipiti accessorius (Haughton), similar to that of the lion, and many mammals (Kelch);
  11. Or from the fascia of the leg (Meckel);
  12. An intermediately arising third head, like 7. above, may be inserted with the lateral head;
  13. Hyrtl describes an instance of this third head separate for a considerable extent;
  14. The entire muscle may be bilaminar;
  15. The lateral head may be entirely tendinous.

The variations of soleus according to Macalister follows.

  1. Soleus: may have a bilaminar fibular head;
  2. Soleus may have a a separate tibial portion inside the tendo Achillis inserted into the os calcis by a special tendon (Quain);
  3. Soleus may be doubled (Cruveilhier);
  4. A special tendon from soleus to the heel (Hellema)

Syn.: m. Gastroc. and soleus; triceps surae, surales, extensor pedis (Theile), Wadenmuskel, mm. gemelli.

Gastroc.: gastrocnemius externus, Jumeaux.
Soleus : gastrocnemius internus, Sohlenmuskel or correctly Schollenmuskel (Henle), Soléaire

Image 137.

Absence of the lateral head of Gastrocnemius
from Shepard, 1880

Image 135

Gastrocnemius tertius
1a.: The CT scan on the left reveals an asymmetrical muscle mass (arrows) in the right popliteal fossa. The muscle mass joins the medial head of the right gastrocnemius muscle. 1b.: On the right side is a diagrammatic representation of the third head (*) of gastrocnemius that was redrawn form Chudzinski, 1882). The cut lines U, M, L correspond to the CT images shown on the left side. LH; Lateral head of gastrocnemius, MH; Medial head of gastrocnemius.

Image 89

Twelve varieties of the third head of gastrocnemius
(redrawn from Frey, H., 1919)

  1. Origin: Lateral to tibial nerve and popliteal vessels; Insertion: lateral head of gastrocnemius muscle.
  2. Origin: Lateral to tibial nerve and popliteal vessels; Insertion: lateral head of gastrocnemius muscle.
  3. Origin: Lateral to tiial nerve and popliteal vessels; Insertion: lateral head of gastrocnemius muscle.
  4. Origin: Lateral to tibial nerve and popliteal vessels; Insertion: medial head of gastrocnemius muscle.
  5. Origin: Lateral to the popliteal vessels; Insertion: medial head of gastrocnemius muscle.
  6. Origin: Medial to the tibial nerve and popliteal vein, lateral to the popliteal artery; Insertion: medial head of gastrocnemius muscle.
  7. Origin: Medial to the tibial nerve and popliteal vessels; Insertion: medial head of gastrocnemius muscle.
  8. Origin: Medial to the tibial nerve and popliteal vein, lateral to the popliteal artery; Insertion: medial head of gastrocnemius muscle.
  9. Origin: Medial to the tibial nerve and popliteal artery, lateral to popliteal vein; Insertion: medial head of gastrocnemius muscle.
  10. Origin: Medial to the tibial nerve and popliteal vessels; Insertion: medial head of gastrocnemius muscle.
  11. Origin: Medial to the tibial nerve and popliteal vessels; Insertion: lateral head of gastrocnemius muscle.
  12. Origin: Popliteal fossa; Insertion: tendon of gastrocnemius muscle.

Medial; Medial head of gastrocnemius to the left side. Lateral; Lateral head of gastrocnemius to the right side.

Note: The neurovascular bundle in the popliteal fossa is, in part or entirely, potentially vulnerable in types 5, 6, 7, 8, 9, and 11 shown above.

Image 210

Gastrocnemius tertius in a living subject

Image 168

Accessory Soleus
Compare this muscle with Flexor Accessorius Longus.
source unknown.


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