Glossary
Pes anserinus (goose foot)
Quick answer
The pes anserinus, Latin for goose foot, is the spot on the inner upper shin, just below the knee joint, where three tendons join: the sartorius, gracilis and semitendinosus. A small bursa beneath it can become inflamed and cause inner knee pain, says Doha knee surgeon Dr. Pablo Gelber at Aman Hospital.
What it is
The three tendons fan out together onto the tibia, a few centimetres below the inner joint line, in a shape thought to look like a goose's webbed foot. They help bend the knee and resist the shin twisting outwards, supporting the MCL, which lies just beneath them. Between the tendons and the bone sits a fluid-filled sac, the pes anserine bursa, that reduces friction.
Why it matters for patients
Pes anserine bursitis or tendinopathy causes tenderness and pain on the inner knee, slightly lower than the joint itself. It is often worse on stairs, getting up from a chair and at night when the knees touch while lying on the side. It is common in people with knee osteoarthritis, in those carrying extra weight, in women, in people with diabetes and in runners who increase their training quickly.
Because the pain is in a similar area, it is often mistaken for a medial meniscus tear or MCL injury, and the two can coexist. Treatment usually includes load adjustment, strengthening, a pillow between the knees at night and, in some cases, an injection.
Frequently asked questions
How can I tell pes anserine pain from a meniscus tear?
Pes anserine pain is usually a little below the joint line and tender to touch there, while meniscus pain sits on the joint line itself. Examination, and sometimes ultrasound or MRI, helps separate them.
Why does my inner knee hurt at night?
Lying on your side can press one knee on the other right over the pes anserinus. A pillow between the knees often helps, but night pain should still be assessed if it persists.
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