One of the possible causes of calf pain is a plantaris tendon tear. Plantaris is a small muscle that is thought to be vestigial. It has a long tendon that spans over two joints, making it susceptible to tears.
The plantaris muscle runs in the posterior compartment of the leg, as part of the triceps surae muscle group, while its tendon attaches to the calcaneus bone of the foot either independently or after converging with the Achilles tendon. The plantaris tendon stretches over both the knee and ankle joints, which makes it particularly susceptible to rupture, commonly occurring when the knee is extended while the ankle joint is dorsiflexed . It is a frequent injury in tennis players and has sometimes been referred to as tennis leg, although it is generally agreed that this term, more often than not, describes injury of the gastrocnemius muscle, with or without concurrent soleus muscle injury. Loss of limb function is not a typical finding in a plantaris tendon tear (PTT), furthermore, the muscle is capable of repairing itself without the aid of surgery . PTT has features similar to other more serious conditions such as deep vein thrombosis (DVT), Achilles tendon rupture and malignancy, which may need further, sometimes invasive intervention .
Although extremely rare, PTT may occur in isolation, or more frequently in combination with other muscle injuries such as trauma to the Achilles tendon  . It is mostly reported in young active individuals and older patients with a sedentary lifestyle.
Symptoms of PTT are calf pain and tenderness that gradually increase after physical activity is stopped, swelling, and a popping or tearing sound. These are acute in onset. Cases in the past have been diagnosed surgically.
To distinguish a plantaris tendon tear from other disorders, a number of imaging studies are employed . They include the following: