The gastrocnemius is a superficial muscle that is located at the back of the leg. It consists of two bellies, one lateral and one medial, which, together with the soleus muscle, form the structure called triceps surae.
Both muscle bundles originate from the femur and travel through the knee to end at the calcaneal bone, below the ankle. For this reason, it is considered a biarticular muscle and has a fundamental role in maintaining balance, standing and walking.
Location of gastrocnemius. CC BY-SA 3.0, In its final course it becomes a single tendinous element that firmly joins both bellies to the soleus muscle tendon, forming the calcaneus or Achilles tendon, which is the strongest in the body.
The gastrocnemius muscle works to its maximum during physical activity, especially one that involves running or changing speed quickly, as in tennis, soccer, and sprinting, among other sports.
Its injury is frequent in athletes and usually presents from inflammation to complete tears of one of their muscle heads.
Anatomy
The calf is the name given to the posterior region of the leg. It is made up of two muscles, the gastrocnemius or twin, and the soleus that runs below it.
The gastrocnemius is made up of two muscular bellies, one lateral and one medial, which have different origins and a common end tendon insertion.
Origin
The heads that make up the gastrocnemius muscle have different origins. The medial portion begins on a posterior protrusion of the medial aspect of the femur, called the condyle. In this area the presence of a synovial fluid bag can be evidenced, which allows the sliding of both muscle heads.
This head also has fibers that insert near the medial aspect of the knee joint capsule.
Lateral and medial bellies of the gastrocnemius. By Dr. Johannes Sobotta - Sobotta's Atlas and Text-book of Human Anatomy 1909, Public Domain, For its part, the lateral belly begins its journey on the lateral aspect of the femur condyle. From there it continues on its way to the knee where some of its fibers insert near the knee joint.
The twin heads are directed downward, passing to both sides of the back of the knee, where they delimit an area called the popliteal fossa.
Insertion
In the lower third of the leg, both muscle bellies become tendons which unite and form a single structure together with the soleus tendon. This tendon is called the calcaneal tendon or the Achilles tendon.
Insertion of gastrocnemius. By OpenStax College - https://cnx.org/contents/:, CC BY 3.0, This tendon runs for about 15 cm, passes behind the ankle, finally reaching the calcaneal bone where it is inserted.
From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 1242, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 564858
At this point, it is separated from the bone by a synovial sac that facilitates its gliding and prevents friction of the tendon with the calcaneus. The Achilles tendon is the thickest, longest and strongest in the body.
Irrigation
The popliteal artery, a direct branch of the femoral artery, is responsible for supplying the arterial vascular supply to the calf region.
Through its sural, anterior and posterior collateral arteries, as well as its two terminal branches of the anterior tibial and posterior tibial, it penetrates the muscle bellies and forms an important network in this area.
Route of the popliteal artery. From Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See "Book" section below) Bartleby.com: Gray's Anatomy, Plate 551, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 559545
The veins that drain the leg form from the tibial veins, ascending through the popliteal and saphenous veins which flow into the femoral vein.
Innervation
The tibial nerve, coming from the trunk of the sciatic nerve above the popliteal fossa, runs in a downward direction and is located between the two muscular bellies of the gastrocnemius, providing neurological branches along its path.
Route of the tibial nerve. By Henry Vandyke Carter - Henry Gray (1918) Anatomy of the Human Body (See «Book» section below) Bartleby.com: Gray's Anatomy, Plate 832, Public Domain, https://commons.wikimedia.org/w/index. php? curid = 541691
This nerve is one of the most important in the posterior region of the lower limb, being responsible for innervating several of the muscles of the leg and foot.
Features
The gastrocnemius is a muscle with important implications for stability and maintenance of balance.
Its main function is the plantar flexion of the foot, this occurs when standing on tiptoe, for example.
In addition, its insertion above the knee makes it an auxiliary muscle in its flexion.
Functions of the gastrocnemius muscle. By Bessieeboo - Own work, CC BY-SA 3.0, During gait it remains contracted, especially in the first phase, preventing rotation of the tibia and is especially active in runs and jumps.
Its fibers are primarily anaerobic, making it the muscle used in sudden efforts, races, and speed changes.
Injuries
Tearing
Gastrocnemius tear is a relatively common injury in athletes. Depending on its severity, three types are distinguished.
The type I tear involves approximately 5% of the muscle and the patient manifests pain with the contraction. In type II, up to 25% of the muscle mass is torn. In these cases the patient may manifest pain and a feeling of continuous cramping.
For its part, the type III tear involves more than 30% of the muscle. The patient has pain and immobility, hematoma on the calf, and swelling.
Large or complete tears can be felt as an area of depression in the calf and seen as a large area of hematoma on ultrasound.
The diagnosis of tear is made by questioning and physical examination, however, when the rupture is not very evident, in milder cases, imaging tests are used to support the diagnostic suspicion.
Ultrasound is the most widely used test as it is inexpensive, can be performed with portable equipment, and its findings are definitive.
Another advantage of ultrasound is that it can be used to drain areas of fluid or bruise that are in the region.
Hematoma on ultrasound from a gastrocnemius tear. The black area is the hematoma. By © Nevit Dilmen, CC BY-SA 3.0, Type I and II tears are for outpatient management with indication of rest and anti-inflammatory drugs, while type III tears are usually surgical, indicating immobilization and subsequent rehabilitation.
Tendinitis
Inflammation of the muscle and tendonitis is another of the injuries that occur frequently in this muscle.
This condition occurs from overloading it, which ends up irritating the tendon causing significant and often disabling pain.
Achilles tendonitis is treated with the administration of pain relievers and anti-inflammatories in addition to rest.
References
- Bordoni, B; Waheed, A; Varacallo, M. (2019). Anatomy, Bony Pelvis and Lower Limb, Gastrocnemius Muscle. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- Binstead, J. T; Varacallo, M. (2019). Anatomy, Bony Pelvis and Lower Limb, Calf. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- Hsu, D; Chang, KV (2019). Gastrocnemius Strain. StatPearls. Treasure Island (FL). Taken from: ncbi.nlm.nih.gov
- Nsitem, V. (2013). Diagnosis and rehabilitation of gastrocnemius muscle tear: a case report. The Journal of the Canadian Chiropractic Association. Taken from: ncbi.nlm.nih.gov
- Werner, B. C; Belkin, N. S; Kennelly, S; Weiss, L; Barnes, R. P; Potter, H. G; Rodeo, SA (2017). Acute Gastrocnemius-Soleus Complex Injuries in National Football League Athletes. Orthopedic journal of sports medicine. Taken from: ncbi.nlm.nih.gov
- Bright, J. M; Fields, K. B; Draper, R. (2017). Ultrasound Diagnosis of Calf Injuries. Sports health. Taken from: ncbi.nlm.nih.gov