Plantaris
Musculus plantaris
Also known as: freshman's nerve
A small, vestigial muscle with a short belly and the longest tendon in the body. It weakly assists gastrocnemius, is absent in ≈7–10% of people and is a useful tendon graft.
Overview
Plantaris arises from the lower lateral supracondylar line of the femur and the oblique popliteal ligament, just above the lateral head of gastrocnemius. Its small fusiform belly (≈7–10 cm) quickly gives way to a very long, thin tendon. The tendon runs obliquely down between gastrocnemius and soleus to the medial side of the calcaneal tendon, inserting with it or separately on the calcaneus.
It weakly assists plantarflexion and knee flexion. Its high density of muscle spindles suggests that it may act mainly as a proprioceptive organ. The thin tendon is easily mistaken for a nerve during dissection, which earned it the nickname "freshman's nerve". It is harvested as a free tendon graft without functional loss.
Anatomy
- Origin
Inferior end of the lateral supracondylar line of the femur and the oblique popliteal ligament.
- Insertion
Posterior surface of the calcaneus (medial to, or with, the calcaneal tendon).
- Action
Weak plantarflexion of the ankle and flexion of the knee.
- Innervation
Tibial nerve.
- Nerve roots
S1–S2
- Arterial supply
Sural arteries (popliteal artery).
Function
- Weakly assists plantarflexion and knee flexion
- Possible proprioceptive role
Clinical significance
Plantaris rupture
Historically blamed for "tennis leg", but most such injuries are actually medial gastrocnemius tears. Isolated plantaris tears do occur and are self-limiting.
Tendon graft
Harvested for reconstruction of hand flexor tendons or ankle ligaments. Its absence in ≈7–10% must be checked first.
Compiled from standard anatomy and physiology references — see the Muscular System sources. For education only; not medical advice.