1
Background
The distal insertion of the sartorius, gracilis, and semitendinosus tendons forms a structure that resembles the goose’s foot. Therefore, this structure has been called “goose foot” (pes anserinus in Latin).
These muscles are primarily flexors of the knee and accessory internal rotators. They have a protecting role against external rotation and valgus stress on the knee [ ]. The anserine bursa is one of 11 bursae found around the knee, located immediately below the pes anserinus.
The first description of changes in this region in the literature dates back to 1937 when Moschcowitz reported knee pain almost exclusively in women, present when going downstairs or upstairs, when rising from a chair, or having difficulty when flexing the knee [ ].
The distinction between anserine bursitis and tendinitis is difficult clinically due to the proximity of the tissues. However, this distinction is not important because treatment is the same for both conditions.
This condition has been especially observed in long-distance runners [ ]. Etiology includes microtrauma, retraction of posterior thigh muscles, bone exostosis, irritation of the suprapatellar plica, medial meniscus lesions, flat foot, genu valgum, local infection, and foreign body reaction [ ].
Epidemiological studies suggest that anserine tendinopathy is also common in overweight females with osteoarthritis of the knees [ , ]. Diabetes mellitus has been identified in a large proportion of patients with pes anserinus [ ]. Cases of chronic bursitis have been documented in patients with rheumatoid arthritis and knee osteoarthritis [ , ].
Although the majority of authors call this condition “anserine bursitis” the structure responsible for the symptoms remains unidentified in most cases [ ].
The diagnosis is frequently established based on typical patient history and clinical findings, but in some cases, imaging modalities may be required.
Treatment is mainly conservative for this condition.
2
Synonyms
Anserine bursitis.
Goose foot tendinopathy.
3
Clinical Study
3.1
Symptoms
The patient’s history is usually typical and characterized by pain in the medial aspect of the knee, approximately 5 cm below the medial joint line. Signs of degenerative joint disease may be present. This pain may be aggravated when going upstairs or downstairs. However, it can be present in the posteromedial region or in the middle of the knee, without edema, making the differential diagnosis with meniscal lesion a challenge.
Criteria for the diagnosis of this condition was described in 1985 by Larson and Baum [ ]. These criteria include:
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Pain in the anteromedial region of the knee, especially when going upstairs or downstairs.
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Morning pain and rigidity for more than 1 h.
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Nocturnal pain.
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Difficulty rising from a chair or getting out of the car.
3.2
Physical Examination
Tenderness and swelling may be present on palpation of the medial aspect of the knee.
Resisted contraction and stretching of the affected muscles usually reproduce the patient’s pain.
The knee range of motion (ROM) is usually not affected.
4
Differential Diagnosis
Several etiologies of medial knee pain should be considered in the differential diagnosis.
4.1
L3-L4 Radiculopathy
In this case, an associated lumbar pain is present and knee pain is not aggravated on digital pressure of the anserine region.
4.2
Meniscal Cyst
The patient presents with pain, blocked movement, and a palpable mass in the articular line.
4.3
Synovial Osteochondromatosis
The patient usually presents with arthralgia, a palpable mass, and restriction of movement.
4.4
Malignant Tumors
These tumors usually have a solid component which allows to make the differential diagnosis.
5
Imaging
5.1
Standard X-rays
They are usually normal, but can also show bony exostosis or signs of osteoarthritis of the medial compartment ( Fig. 5.1 ).
5.2
Ultrasound
Studies have demonstrated that only a minority of patients with pes anserinus syndrome have specific ultrasound (US) changes.
A marked tendinous thickening and loss of normal fibrillar structure of the symptomatic side compared to the asymptomatic one can be observed. Fluid collection in the symptomatic anserine bursa area may also be noticed.
5.3
CT Scan
Computed tomography (CT) scan can show a well-defined cystic image of low attenuation immediately below the pes anserinus in relation to a bursitis. It should be noted that the distension of the anserine bursa is not always synonymous of bursitis and the observed signs could be related to a case of tendinitis or fasciitis of the pes anserinus [ ].
5.4
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) may be useful in the diagnosis of acute anserine bursitis when fluid accumulation and synovial proliferation are observed [ ]. It is also useful in the evaluation of uncertain masses in the medial region of the knee [ ] ( Figs. 5.2 and 5.3 ).
