plantaris muscle

The plantaris muscle is one of the calf muscles in the superficial posterior compartment of the leg. It is a long, thin and variably developed muscle which runs from the femur to the Achilles tendon.

Summary

Gross anatomy

Origin and insertion

The plantaris muscle arises from the posterosuperior aspect of the lateral femoral condyle, close to the origin of lateral head of gastrocnemius. There is often an attachment to the oblique popliteal ligament. As the plantaris crosses the posterior knee joint, it runs medially.

In the calf, it lies in between the medial head of the gastrocnemius and soleus.

Distally, the tendon inserts into the medial aspect of the Achilles tendon.

Plantaris can have variable size, but in most cases is difficult to demonstrate on routine MRI studies.

Function

Plantaris acts weakly to plantar flex the foot and flex the knee. It is considered a vestigial muscle, and can be used as a tendon graft in reconstructive orthopedic surgery.

Variant anatomy

In up to 10% of the population, the plantaris is absent and in a smaller number it may be duplicated .

Related pathology

  • fluid collections; it is most easily visualized when there is fluid collection in the myofascial junction between gastrocnemius and soleus, commonly secondary to strain of the medial head of gastrocnemius (tennis leg).
  • plantaris friction syndrome