Test your knowledge: the pes anserinus
Which muscles insert at the pes anserinus (goose’s foot)?
You may expect something called the goose’s foot to be in or near the foot itself, except it is actually located near the knee. Instead of describing a location, this rather odd anatomical term refers to the shape of the insertion of three muscle tendons that blend together to make up the pes anserinus (Latin for goose’s foot). These muscle tendons, in combination with an underlying bursa, can be the cause of pain just distal to the knee joint and medial to the tibial tuberosity. This bursitis related pain should be differentiated from other causes of knee pain and treatment should include measures to reduce inflammation of the bursa.
The pes anserinus is a combination of the tendons of the sartorius, gracilis, and semitendinosus muscles. As these tendons approach their insertion point, which is just medial to the tibial tuberosity, they combine and expand out to resemble a goose’s foot or the pes anserinus.
The muscles of the pes anserinus arise from three different compartments in the thigh. The sartorius originates in the anterior compartment from the anterior superior iliac spine (ASIS), and is involved in flexion and lateral rotation of the thigh, and flexion of the knee. The gracilis, the most medial muscle in the medial compartment, originates from the body of the pubis and is involved in adduction of the thigh. And finally, the semitendinosus, one of three hamstring muscles in the posterior compartment of the thigh, originates from the ischial tuberosity and is involved in extension of the thigh and flexion of the knee. Given their different origins, paths, and actions, as these muscles approach their insertion however, they all add stability to the medial aspect of the knee when it is in extension.
Lying deep to the pes anserinus and the muscle tendons is the tibial collateral ligament. Between these structures lies the anserine bursa. Like any other bursa, it is a fluid filled sac that provides cushioning between anatomical structures; in this case between the pes anserinus, the tibial collateral ligament, and the underlying bone.
The presence of the anserine bursa deep to the pes anserine and its muscle tendons, means that this region can be vulnerable to pain associated with bursitis. Repeated flexion and extension of the knee (which occurs during running or climbing stairs), in which tension of the pes anserine muscle tendons will increase pressure on the bursa, can cause the anserine bursa to become inflamed resulting in pain and swelling medial to the tibial tuberosity. Modified activity is essential for resolution of this type of injury, as well as treatment for inflammation of the bursa.