Pes anserinus refers to insertion of the conjoined tendons of the sartorius, gracilis, and semitendinosus muscles on the proximal medial tibia. The name pes anserinus ("goose foot" in Latin) derives from the fact that the conjoined tendons look like a webbed foot. Pes anserine tendonitis is inflammation of these tendons. Often, there is a bursa that is inflamed (pes anserine bursitis), but there does not have to be bursal involvement. The condition of pain in the proximal medial aspect of the tibia at the insertion of the tendons is generally known as pes anserine pain syndrome.

In the acute setting, it is not important for a primary care or emergency medicine doctor to know if there is bursal involvement; pes anserine pain syndrome and pes anserine bursitis are approached similarly.

Sports may be a contributing factor (running, basketball, racket sports, dancing). Patients with genu valgum (eg, being "knock-kneed") and who are obese may be at increased risk, in particular women. Stiffness or tightness of the hamstrings contributes to the etiology of this condition.

Pes anserine pain syndrome can be associated with concomitant medial compartment knee osteoarthritis, medial collateral ligament injury (MCL), and medial meniscus tear of the knee.