The plantaris is one of the superficial muscle
s of the superficial posterior compartment of the leg
, one of the fascial compartments of the leg
It is composed of a thin muscle belly and a long thin tendon
. While not as thick as the achilles tendon
, the plantaris tendon (which tends to be between in length) is the longest tendon in the human body
. Not including the tendon, the plantaris muscle is approximately long and is absent in 8-12% of the population. It is one of the plantar flexors
in the posterior compartment of the leg, along with the gastrocnemius
muscles. The plantaris is considered an unimportant muscle and mainly acts with the gastrocnemius.
The plantaris muscle arises from the inferior part of the lateral supracondylar ridge
of the femur
at a position slightly superior to the origin of the lateral head of gastrocnemius
. It passes posterior to the knee joint
in an inferomedial direction and becomes tendinous distally to insert into the Achilles tendon
. It occasionally separately inserts into the medial side of the calcaneus
The plantaris muscle is innervated by the tibial nerve
, a branch of the sciatic nerve
in the sacral plexus
. Signaling for contraction begins in the frontal lobe
of the brain
with the pre-central gyrus
(primary motor cortex
). Upper motor neuron
s 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
, then the fibers continue down the contralateral side of the spinal cord
. Upper motor neurons synapse with lower motor neuron
s at the anterior horn of the spinal cord
in the sacral plexus (formed from the anterior rami of spinal nerves
L4, L5, S1–4). The lower motor neuron fibers continue down the sciatic nerve and then diverge into the tibial and common fibular nerve
s. 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.
The muscle may arise from the oblique popliteal ligament
. Interdigitations with the lateral head of the gastrocnemius
and a fibrous extension of the muscle to the patella
are not unusual.
The plantaris acts to weakly plantar flex
the ankle joint
and flex the knee joint
The plantaris muscle may also provide proprioceptive
feedback information to the central nervous system
regarding the position of the foot. The unusually high density of proprioceptive receptor end organs supports this notion.
[Moore, Keith L; & Dalley Arthur R (2008). ''Clinically Oriented Anatomy'' (6th ed.). Lippincott Williams and Wilkins. ]
Its motor function is so minimal that its long tendon can readily be harvested for reconstruction elsewhere with little functional deficit. Often mistaken for a nerve by new medical students (and thus called the "freshman nerve"), the muscle was useful to other primate
s for grasping with their feet.
[Andor, W.J.M., Glaudemans, Rudi A.J.O. Dierckx, Jan L.M.A. Gielen, Johannes (Hans) Zwerver (2015). ''Nuclear Medicine and Radiologic Imaging in Sports Injuries''. Springer. p. 762]
A common injury that is normally attributed to the plantaris muscle is a condition called ''tennis leg''. Although pain in the calf can be attributed to a rupture of the plantaris muscle, recent ultrasound research has shown that tennis leg more commonly arises from tears in the musculotendinous junction of the medial gastrocnemius. In one clinical study, 94 out of 141 patients (66.7%) diagnosed with tennis leg were found with a partial rupture of the gastrocnemius muscle, while rupture of the plantaris tendon was only seen in 2 patients (1.4%).
Injury may occur from running, jumping, or pushing off one leg in sports such as tennis, basketball and soccer, which require quick foot movement in a certain direction. Isolated plantaris muscle strains are rare, and ruptures normally occur in conjunction with injury to other muscles in the posterior compartment of the lower leg. Symptoms of a plantaris muscle rupture may include an audible popping sound in the area during physical activity, swelling, pain in the back of the lower leg, and persistent soreness. Ankle flexion may also be painful.
File:Plantaris muscle - animation.gif|Animation
File:Sobo 1909 304.png|The plantaris is visible under the gastrocnemius.
File:Plantaris muscle by Sanjoy Sanyal.webm|Dissection video (59 s)
Image:Gray1242.png|The synovial sheaths of the tendons around the ankle. Medial aspect. (Tendon of Plantaris labeled at bottom right.)
Image:Gray438-Musculus plantaris.png|Muscles of the back of the leg. Superficial layer.
File:Gray440 - Plantaris.svg|Cross-section through middle of leg. Tendon of plantaris is located between soleus and gastrocnemius.
File:Plantaris muscle 2.jpg|Plantaris muscle
File:Space of the gastrocnemius and soleus - text.png|Plantaris tendon runs between soleus and gastrocnemius. Plantaris tendon is indicated by white arrow-heads.
Category:Muscles of the lower limb