The term pes anserinus is Latin for "goose's foot." The pes anserinus, located near the knee, is a group of three tendons that come together to a common point on the side of the knee. Apparently, early anatomists thought that this tendon group resembled the three webbed toes of a goose. The pes anserinus bursa is the fluid-filled sac located near these tendons. This bursa is susceptible to inflammation, or bursitis, and it can be the source of knee pain in athletes and others.
Anatomy
The three muscles whose tendons come together to form the pes anserinus originate in the upper thigh. These muscles are the sartorius, the gracilis and the semitendinosus. The tendons attached to these muscles insert on the inner front part of the tibia bone, just an inch or two below the actual knee joint. The pes anserinus bursa is located between a knee joint ligament and this tendon. The bursa serves to mitigate the effects of friction between the tendon and the joint as the knee flexes and extends.
Symptoms
The pain of pes anserinus bursitis tends to be fairly well localized to the location of the bursa. This pain can be of a deep, achy quality and usually comes on gradually, increasing over a period of time. It may be more noticeable when getting up out of a chair. It is rarely aggravated by normal walking on a level surface, but it will tend to be aggravated by ascending or descending stairs. For an athlete, the symptoms may be much more pronounced when running up and down hills.
Causes
This condition typically results from some type of overuse. For the running athlete, this might mean a sudden increase in training intensity or training conditions, such as running hills or stairs. Just increasing mileage too quickly may also be a trigger. Hiking over uneven terrain might be a cause, or pushing a lawn mower around a hilly yard. Some people may be anatomically predisposed to developing pes anserinus bursitis. A study published in The Journal of Clinical Rheumatology in 2007 concluded that people who have an excessive valgus angle at the knee--commonly called "knock-kneed"--are at increased risk for pes anserinus bursitis.
Diagnosis
The diagnosis is largely based on the location and description of the pain. There will usually be tenderness to direct pressure over the bursa. Sometimes swelling will be evident. X-rays are rarely helpful in the diagnosis but may be taken to rule out a stress fracture, which can sometimes cause similar symptoms. An MRI of the knee will reveal characteristic findings of fluid swelling beneath the tendons of the pes anserinus. This finding is described in 1995 article in the journal, Radiology.
Treatment and Prevention
Initial treatment strategies focus on reducing the inflammation. Rest and ice applications can be very helpful. Non-steroidal anti-inflammatory medications may also be recommended early on. Sometimes cortisone injections are considered as a measure to curb the inflammation. Later strategies may focus on stretching of the hamstrings and strengthening the quadriceps with a goal of gradually resuming normal activities without provoking a recurrence of the bursitis.
References
- "Journal of Clinical Rheumatology"; Risk Factors for Pes Anserinus Tendinitis/Bursitis Syndrome: a Case Control Study; J Alvarez-Nemegyei; April 2007.
- "Radiology"; Acute Pes Anserine Bursitis: MR Imaging; J Forbes, C Helms, D Janzen; February 1995.
