The plantaris is a vestigial muscle with a very short belly and an extremely long, thin tendon running between the gastrocnemius and soleus to insert on the medial calcaneus. Absent in approximately 7 to 10 percent of people, it contributes negligibly to plantarflexion strength, but its tendon is used as a graft in Achilles tendon reconstruction. Its clinical significance lies primarily in plantaris rupture, which produces the classic tennis leg presentation and must be distinguished from an Achilles tendon tear.
| Origin | Lateral supracondylar line of the femur above the lateral head of the gastrocnemius |
|---|---|
| Insertion | Posterior surface of the calcaneus medial to the Achilles tendon |
| Nerve Supply | Tibial nerve (L4, L5, S1, S2) |
| Blood Supply | Sural artery |
| Actions | Weak plantarflexion of the ankle; Weak flexion of the knee |
|---|
Its mechanical contribution to plantarflexion is so small as to be clinically irrelevant, as its extremely small cross-sectional area relative to the gastrocnemius makes its force production negligible.
Plantaris rupture produces the sudden sharp calf pain and pop at the musculotendinous junction, classically during running or racket sports in middle-aged athletes, that is called tennis leg. The presentation is similar to Achilles tendon rupture but the Thompson test is negative and patients retain some plantarflexion strength. Ultrasound or MRI confirms the diagnosis. Conservative management with compression and gradual loading resolves most cases within 6 to 8 weeks.
The plantaris belly is not individually palpable as it is buried between the gastrocnemius and soleus, but the clinical picture of medial calf pain with a negative Thompson test suggests plantaris over Achilles pathology.
Musculotendinous junction tear during running or racket sports producing sudden medial calf pain and pop with a negative Thompson test, distinguished from Achilles rupture by ultrasound or MRI and managed conservatively.
