Pes anserine is actually french, and translated it means “goose foot”. It is a triangular (think of the shape of a goose foot) area on the anteromedial aspect of the knee 1-4 cm below the medial joint line where three different muscles insert. From anterodistal to posteroproximal the order of insertion is the sartorius, the gracilis, and the semitendinosus. Just deep to these tendons is the medial collateral ligament better known by its abbreviation: the MCL
The sartorius is the longest muscle in the body. It spans from the anterior superior iliac spine (put your hands of your hips, your pointer finger is right on the ASIS!), crosses the hip joint, forms the roof of the adductor canal which holds the femoral artery, vein, and part of the nerve. Finally it crosses the knee joint to insert on the pes anserine. The gracilis is a groin muscle. The semitendinosus is one of the three muscles that makes up your hamstring. Fun fact: it is the most common autograph used in ACL reconstruction.
The tendons of these three muscles rub against a part of the tibia as the knee goes through its full range of motion. Just like in the movies where a guy is hanging from the edge of a cliff by a rope and the rope starts to fray as it rubs against the rock, the tendons can become irritated. Between the tendon and the bone is a lubricating sac called a bursa. It reduces friction to almost zero normally, but when irritated it becomes inflamed and fills with fluid. Bursa are well innervated, so when it becomes inflamed and the tendons continue rubbing over (or the doctor pushes on it) it you will definitely feel it!
Pain over the pes anserine isn’t always caused by inflammation of the bursa however. Other conditions associated with anserine pain in the absence of an inflamed bursa include:
Genu valgum (knock knees)
Genu varum (bow leggedness)
Osteoarthritis (possibly due to referred pain).
While genu valgum/varum place an obvious abnormal strain on the muscles which attach to the pes anserine, we don’t fully understand why some of the other conditions cause or refer pain to the pes anserine at this time.
Once we have a solid diagnosis of pes anserine bursitis, the goals of treatment are to reverse the cause of the pain. Bursal inflammation is due to overuse. The pain then leads to atrophy of the stabilizing musculature of the knee including the sartorius, gracilis, semitendionsis, and quadriceps muscles. The treatment therefore will always start with resting the knee. That will stop further irritation. In order to reverse the inflammation oral NSAIDs are added along with ice and elevation. If that doesn’t do the trick, a steroidal anti-inflammatory medication (corticosteroids) can be injected into the bursa. Once the inflammation is controlled, a progressive course of physical therapy and exercise will allow reversal of atrophy leading to a full recovery!
Scott Cochran, MS-IV
David Carfagno, D.O., C.A.Q.S.M.
- Alvarez-Nemegyei J. Risk factors for pes anserinus tendinitis/bursitis syndrome: a case control study. J Clin Rheumatol 2007; 13:63.
- Brookler MI, Mongan ES. Anserina bursitis. A treatable cause of knee pain in patients with degenerative arthritis. Calif Med 1973; 119:8.
- Canoso, JJ. Knee bursitis. In: UpToDate, Isaac, Z (Ed), UpToDate, Waltham, MA, 2016
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