Pes anserinus is the area where the tendons of three hamstring muscles (semimenbranosus, gracilis, and sartorius) is conjoined and inserts onto to the inner tibia bone. The name is derived from its resemblance of a goose’s webbed foot (pes anserinus, in Latin). Pes anserine bursa refers to the small sac (bursa) of synovial fluid that cushions the tibia bone and pes anserinus tendon.
Pes anserine bursitis is common among track and field athletes that overuse hamstring muscles, or excessive walking in length/elevation.
Other causes include direct blow to the area, but is also common for those with lower limb deformities such as knock-knees or flat feet.