Logan Steele
The plantaris muscle is a small, short and slender muscle that runs from the femur to the Achilles tendon. It is located in the posterior compartment of the leg, behind the knee and into the calf. The muscle is considered vestigial and is absent in a small percentage of the population. The plantaris tendon is the longest tendon in the human body and is often referred to as the 'freshman's nerve' due to its resemblance to a nerve. The muscle has a weak motor function and is associated with injuries such as tennis leg.
| Characteristics | Values |
|---|---|
| Muscle Type | Small, short and fusiform |
| Muscle Belly | Short and fleshy |
| Muscle Belly Length | 5-10 cm |
| Tendon | Long, thin and slender |
| Tendon Length | 30-45 cm |
| Muscle Belly Variability | Variable in thickness and length |
| Muscle Absence | 6-20% of the population |
| Muscle Duplication | 10% of the population |
| Muscle Origin | Lateral supracondylar line of the femur |
| Muscle Insertion | Medial side of the tubercle of the calcaneus |
| Neural Innervation | Tibial nerve (S1, S2) |
| Blood Supply | Popliteal artery |
| Function | Weakly assists gastrocnemius and soleus muscles |
| Additional Function | Proprioceptive feedback to the central nervous system |
| Common Injury | Tennis leg |
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What You'll Learn
Location and structure
The plantaris is a small, short and slender muscle with a short belly and a long, thin tendon. It is located in the posterior compartment of the leg, extending behind the knee and into the sural region (calf). The muscle belly is situated in the proximal third of the leg, between the popliteus muscle anteriorly and the lateral head of the gastrocnemius muscle posteriorly. The belly of the plantaris is typically 5 to 10 cm long and is variable in thickness and length. In some cases, the muscle has two bellies separated by a tendon.
The plantaris tendon is the longest tendon in the human body, measuring between 30 and 45 cm in length. The tendon travels inferomedially along the medial border of the gastrocnemius, between the medial head of the gastrocnemius and the soleus muscle in the middle third of the leg. The tendon inserts onto the posterior surface of the calcaneus, medial to the calcaneal tendon (also known as the Achilles tendon). In some cases, the plantaris tendon may join the calcaneal tendon or merge with the flexor retinaculum of the ankle or leg fascia.
The plantaris muscle arises from the inferior part of the lateral supracondylar ridge of the femur, just above the lateral head of the gastrocnemius muscle. The origin of the muscle is typically on the popliteal surface of the femur, above the lateral condyle and the knee joint capsule. The attachment often extends onto the oblique popliteal ligament. The muscle belly crosses the popliteal fossa inferomedially, forming the inferolateral border of the fossa.
The plantaris is one of the most superficial muscles in the posterior compartment of the leg, with only the gastrocnemius muscle overlying it. It is visible under the gastrocnemius and descends between the gastrocnemius and the soleus, the latter being located deep to the plantaris. The muscle is innervated by the tibial nerve, a branch of the sciatic nerve, and receives blood from the popliteal artery and the lateral sural artery, a branch of the popliteal artery.
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![[(Anatomy and Injuries of the Foot and Ankle)] [Author: Anatomical Chart Company] published on (December, 2004)](https://m.media-amazon.com/images/I/5131TGGEB-L._AC_UY218_.jpg)
Function
The plantaris muscle is a small, short and slender muscle with a long tendon. It is one of the superficial muscles of the superficial posterior compartment of the leg, extending behind the knee and into the calf. The muscle belly is variable in thickness and length, and in some cases, the muscle has two bellies separated by a tendon. The plantaris tendon is the longest tendon in the human body.
The function of the plantaris muscle is a subject of debate. It is involved in plantar flexion of the foot at the ankle joint and knee flexion at the knee joint. However, it only weakly assists the gastrocnemius and soleus muscles in these movements. It is considered to have become less important when human ancestors evolved from tree-climbing to bipedalism.
The plantaris muscle contains a high density of muscle spindles, or proprioceptive receptors. This suggests that it may act as a proprioceptive organ, providing feedback to the central nervous system about the position of the foot. However, since proprioceptive and flexor functions are not affected when the plantaris muscle is absent or removed, some studies argue that it may be vestigial or still developing in humans.
The plantaris tendon is often harvested for reconstruction or used as a tendon graft in surgery, as its removal does not typically hinder lower extremity function.
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Pathology
The plantaris muscle is a small muscle with a short belly and a long, slender tendon. It is one of the most superficial muscles in the posterior compartment of the leg. The muscle is prone to rupture due to its location across the knee and ankle joints.
In terms of pathology, the plantaris muscle is important in the differential diagnosis of calf strains and any pain arising from the proximal posterior aspect of the leg. A common injury attributed to the plantaris muscle is tennis leg, which is characterised by a rupture of the muscle or tendon, an audible popping sound during physical activity, swelling, pain in the back of the lower leg, and persistent soreness. However, recent studies have shown that tennis leg may be more commonly caused by tears in the musculotendinous junction of the medial gastrocnemius.
Isolated plantaris muscle strains are rare, and ruptures usually occur in conjunction with injuries to other muscles in the posterior compartment of the lower leg. The plantaris tendon can be visualised using ultrasound when there is fluid collection in the myofascial junction between the gastrocnemius and soleus muscles.
The plantaris tendon is commonly used as a tendon graft in reconstructive surgery, as its removal does not typically hinder lower extremity function when the soleus and gastrocnemius muscles are intact. The tendon is also used to bridge gaps or reinforce repairs during surgical procedures requiring donor tendons.
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Treatment
The plantaris muscle is a small, thin muscle with a short belly and a long, slender tendon that runs alongside the Achilles tendon. It is located in the calf, at the posterior compartment of the leg, and is involved in flexing the ankle and knee joint.
The plantaris muscle is typically treated non-surgically, with conservative treatment methods. The injury is usually less severe than other calf muscle injuries, and full recovery can take up to eight weeks.
The first steps in treating a plantaris muscle injury are rest, ice, compression, and elevation (R.I.C.E). This may be all that is required for a minor strain. Anti-inflammatory drugs may be recommended for short-term pain relief and to reduce inflammation. Crutches may also be used to aid mobility if weight-bearing is painful.
To aid recovery, soft tissue manipulation, and massage can be used to stimulate repair. Elastic support from foot to knee can also be beneficial.
Physical therapy is an important aspect of treatment and recovery. Range of motion exercises, soft tissue manipulation, and a gradual strengthening program can help to improve mobility and strength.
Strength training is also important for treating plantaris tendon injuries. Heel raise exercises, also known as calf raises, can help to load the Achilles and plantaris tendons, building strength. However, it is important to start with floor-level exercises to limit compression between the tendons and only progress to exercises over a step once the tendon has built strength.
In rare cases, surgery may be required to treat a plantaris injury. Surgical resection of the plantaris has been shown to improve tendon structure and decrease pain.
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Innervation
The plantaris muscle is a long, thin muscle that runs down the posterior aspect of the lower leg. It is innervated by the tibial nerve, a branch of the sciatic nerve in the sacral plexus. The tibial nerve arises from the S1 and S2 spinal nerves.
The plantaris muscle is one of the most superficial muscles within the posterior compartment of the leg. It is located superficial to the soleus muscle and deep to the gastrocnemius muscle. The muscle belly is variable in thickness and length. The muscle is considered vestigial and is absent in around 7-20% of individuals.
The tibial nerve provides innervation for the plantaris muscle and other muscles of the posterior lower leg compartment. Signalling for contraction begins in the frontal lobe of the brain with the pre-central gyrus (primary motor cortex). Upper motor neurons are stimulated and send a signal through the internal capsule and down the corticospinal tract. Decussation of the lateral corticospinal tract occurs in the medullary pyramids, and the fibres continue down the contralateral side of the spinal cord.
Upper motor neurons synapse with lower motor neurons at the anterior horn of the spinal cord in the sacral plexus. The lower motor neuron fibres continue down the sciatic nerve and then diverge into the tibial and common fibular nerves. The tibial nerve runs medially at the knee joint. When the tibial nerve receives an action potential, the plantaris muscle contracts, providing weak plantar flexion of the foot and weak flexion of the knee.
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Frequently asked questions
The plantaris muscle is a small muscle with a short belly and a long, thin tendon that runs behind the knee and into the calf of the posterior leg.
The plantaris muscle acts with the gastrocnemius to provide weak plantar flexion of the foot and weak flexion of the knee.
The plantaris muscle is prone to rupture, especially during sports that require quick foot movements in a certain direction, such as tennis, basketball, and soccer. It is also important to differentiate the plantaris muscle from the gastrocnemius when diagnosing calf strains and pain in the proximal posterior leg.
The plantaris muscle originates from the lateral supracondylar line of the femur, just above the lateral head of the gastrocnemius muscle. Its tendon then travels along the medial border of the gastrocnemius and soleus muscles, inserting into the Achilles tendon or the medial side of the calcaneus (heel bone).
The plantaris muscle is nicknamed the "freshman's nerve" because its long, thin tendon is often mistaken for a nerve by first-year medical students during dissections.
