Plantaris Muscle

The plantaris Muscle is a small muscle with a short belly and a long tendon. It’s one of the superficial group of calf muscles.

This vestigial muscle is absent in 5–10% of people and is highly variable in size and form when present (most commonly a tapering slip about the size of the small finger). It acts with the gastrocnemius but is insignificant as either a flexor of the knee or a plantarflexor of the ankle.

The superficial group of calf muscles (muscles forming prominence of “calf” of posterior leg) includes the gastrocnemius, soleus, and plantaris.

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Plantaris Muscle Anatomy

The plantaris muscle has been considered to be an organ of proprioception for the larger plantar flexors, as it has a high density of muscle spindles (receptors for proprioception). Its long, slender tendon is easily mistaken for a nerve (and hence dubbed by some as the “freshman’s nerve”).

The plantaris tendon runs distally between the gastrocnemius and soleus and occasionally suddenly plantaris muscle rupture with a painful pop during activities such as racquet sports. Because of its minor role, the plantaris tendon can be removed for grafting (e.g., during reconstructive surgery of the tendons of the hand) without causing disability.

See Also: Ankle Anatomy

Origin

The plantaris originate from inferior aspect of lateral supracondylar line of distal femur, at a position slightly superior to the origin of the lateral head of gastrocnemius muscle.

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.

Insertion

The plantaris passes posterior to the knee joint in an inferomedial direction and becomes tendinous distally to insert into the Achilles tendon. It inserts onto middle 1/3 of the posterior calcaneal surface, just medial to Achilles tendon.

Innervation

Plantaris muscle is innervated by the tibial nerve (L5, S1, S2) (L5, S1, S2).

Blood Supply

It’s supplied by the sural arteries.

Action

The plantaris acts as a plantar flexor of ankle; it also flexes the knee.

Plantaris Muscle Rupture

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.

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.

The immediate treatment of muscle injury involves the RICE (rest, ice, compression, elevation) protocol. Then the treatment routine included the use of cryotherapy and passive stretching, followed by a 5-min period of ultrasound therapy. In terms of the resting component, a brief period of immobilization is needed in order to allow the body to provide new granulation tissue with the needed tensile strength to withstand the forces generated by muscle contractions.

Surgical treatment (fasciotomy) is indicated in situations when an associated posterior compartment syndrome has complicated the evolution of the signs and symptoms because of the swelling and hematoma formation associated with a rupture or tear.

References & More

1. Clinically Oriented Anatomy – 8th Edition
2. Spina AA. The plantaris muscle: anatomy, injury, imaging, and treatment. J Can Chiropr Assoc. 2007;51(3):158-65. PMID: 17885678; PMCID: PMC1978447. Pubmed
3. Helms CA, Fritz RC, Garvin GJ. Plantaris Muscle injury: Evaluation with MR Imaging. Radiology. 1995;195:201–203. [PubMed]