The plantaris muscle is a fine rope-like tendon running next to the larger Achilles Tendon. Its function is to work with the Achilles to flex the ankle and knee joint by extending from the outside (lateral) back of the femur (allowing you to stand on your toes or point your foot). The plantaris starts just above the lateral head of the gastrocnemius muscle and runs beneath the gastrocnemius and soleus muscles located near the inner (medial border) of the Achilles tendon and attaches to the medial side of the Calcaneus (heel bone).
Mechanism of Injury
Commonly called Tennis leg, a tear or rupture of the plantaris involves the plantaris muscle and possibly the medial head or inside of the gastrocnemius muscle which is the larger of the two calf muscles. Injuries are usually the result of a sudden muscular action such as reaching out for a tennis shot.
- Patients often report hearing a pop in the back of their calf.
- Pain and swelling most commonly at the junction of the calf muscle and the Achilles tendon, the location of the rupture.
- Palpation of a defect at the site of pain and swelling is usually possible.
- The flexion compression test of the gastrocnemius muscle for Achilles rupture is negative, meaning that the Achilles still flexes the foot when the Plantaris is ruptured.
Examination and diagnosis
Plantaris muscle rupture can be diagnosed via history and physical examination. Ultrasound imaging and MRI can confirm the injury. Unless associated with bony injury, x-rays of the area will not be useful. Injury to the plantaris muscle can present with similar clinical features to conditions like deep vein thrombosis, rupture of Baker's cyst, and tumors. An MRI is accurate in differentiating and characterizing plantaris muscle injury.
Treatment and rehabilitation
Once the diagnosis is confirmed and Achilles tendon rupture ruled out, the following treatments are effective for reducing pain and swelling, and speeding recovery:
- Ice and compression.
- Soft tissue manipulation and massage to directly stimulate repair.
- Elastic support (e.g., ACE, TEDs stocking, Tubigrip) from foot to knee.
- Patient can use crutches in the early phase if weight bearing is painful.
- Physical therapy with range of motion exercises and soft tissue manipulation followed by a gradual strengthening program is an important aspect of management.