Plantaris-The unknown muscle of the calf


“It felt like I got kicked in the back of the leg” is one of the scariest phrases for athletes. When that feeling occurs in the heel it usually means the Achilles tendon has ruptured. Oftentimes that means surgery, though there is literature that says surgical repair may not be necessary; but either way, the athlete is facing a long rehabilitation.

However, that same feeling can also be felt higher up in the calf. When that happens, the athlete can see significant swelling, pain and sometimes bruising. When they present to the office, they often believe they tore one of the 2 large muscles of the calf, the gastrocnemius or soleus. However, there is a 3rd, small and often unknown muscle of the calf that is more frequently the culprit, the plantaris.

The plantaris muscle starts from the bottom of the thigh bone (femur) and runs behind the knee into the top portion of the calf. The tendon then runs the rest of the way down the calf and attaches to the heel next to the Achilles tendon. Often the rupture is located where tendon and muscle attach, which is why the sensation is felt in the middle of the calf and there isn’t much bruising. If the tear is higher up in the muscle belly, there will be significant swelling too.

If the tendon tears, then doesn’t it have to be fixed like the Achilles or rotator cuff? The answer is no. The plantaris provides no significant contribution to the functions of the other muscles in the calf, which are pointing the foot down towards the ground and flexing the knee. There is some belief that it has some other roles in the movements of the lower leg, but again, nothing vital. Therefore, treatment involves relieving the immediate symptoms of pain and swelling, then regaining the strength and ROM of the calf muscles with therapy.

Calf injuries can be very scary as the first thoughts often go towards the Achilles tendon and surgery. However, when the location of the injury is higher up, the structure commonly damaged is the plantaris. When that is the case, with accurate diagnosis and good therapy, the athlete can return to previous levels of activity and performance without surgery.