Approach Considerations
The diagnosis of pes anserine bursitis usually is made on clinical grounds, and further workup is not necessarily indicated. In unusual cases (those that are persistent or suggestive of infection), a further workup can be obtained. In the rare cases where infection appears possible, appropriate laboratory studies may be ordered. If other pathology is suggested, radiography, radionuclide bone scanning, rheumatoid factor measurement, or other rheumatologic testing should be considered.
A diagnostic or therapeutic lidocaine or lidocaine-corticosteroid injection into the area of the pes anserine bursa may help the clinician to determine the contribution of pes anserine bursitis to a patient’s overall knee pathology, as well as possibly alleviate the patient’s symptoms.
Laboratory Studies
Infections of the pes anserine bursa are very rare and occur primarily in immunocompromised patients. These patients typically have a localized area of warmth, pain, and swelling. In such cases, a standard laboratory workup for infection is indicated, including determination of the erythrocyte sedimentation rate (ESR), a complete blood count (CBC) with differential, and measurement of the C-reactive protein (CRP) level.
If the bursa or joint is aspirated for this or other reasons, analysis of the fluid may include a cell count, assessment of fluid appearance, Gram staining, culture, and polarized light microscopy.
Radiography
As a rule, radiography of the knee is not indicated for bursitis. However, plain radiographs (standing anteroposterior [AP] and lateral views) can be useful for ruling out a proximal tibial stress fracture, as well as for helping to diagnose concurrent pathology, such as medial compartment arthritis, osteochondroma, or osteochondritis dissecans, which could contribute to tight hamstrings and pes anserine bursal irritation. Arthritis may be observed in older adults. In rare cases, young, athletic patients have an exostosis in the metaphyseal area.
Ultrasonography
Ultrasonography can facilitate the diagnosis of pes anserine bursitis. [28, 29] Large, cystic bursal swellings have been identified by means of ultrasonography and computed tomography (CT). However, published reports suggest that in most suspected cases, ultrasonographic findings are lacking. [30] This lack of ultrasonographic findings has led some to question the frequency of pes anserine bursitis and its accepted pathophysiology.
In one study, only 3 of 29 patients with suspected pes anserinus tendinobursitis were found to have tendinitis on ultrasonographic images when compared with the uninvolved extremity or healthy controls. [30] In a study of patients with type 2 diabetes mellitus, 4 out of 14 patients who were clinically diagnosed with pes anserine tendinobursitis syndrome were found to have ultrasonographically apparent morphologic changes in the pes anserine tendons. [20]
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is the preferred imaging technique for confirming the diagnosis of pes anserine bursitis and differentiating it from concurrent pathology of the medial compartment. [31, 32] On MRI, the pes anserine bursa is observed between the pes anserinus (ie, the insertion of the conjoined gracilis, semitendinosus, and sartorius tendons into the anteromedial proximal tibia) and the upper tibial metaphysis.
The appearance of pes anserine bursitis on MRI is characterized by increased signal intensity and fluid formation around the area of the pes anserinus bursa. A collection of fluid with low signal intensity is observed on T1-weighted images, and a homogenous increase in signal intensity is observed on T2-weighted images. Fluid-filled anserine bursae have been reported with a prevalence of 5% in asymptomatic knees; consequently, the diagnosis of pes anserine bursitis cannot be based solely on MRI findings. [31]
Limited axial and sagittal T2-weighted or T2 gradient-echo sequences usually are adequate for diagnosis. More extensive imaging with additional planes may be required to exclude other clinically relevant possibilities. Axial images are particularly helpful for differentiating fluid in the pes anserine bursa from other medial fluid collections, such as Baker and meniscal cysts, bone cysts, and fluid in the semimembranosus bursa. [33] MRI also is helpful for ruling out a proximal tibial stress fracture. [31]
At least 1 case of chronic pes anserine bursitis manifested as a solid, inflammatory synovial mass. One report describes tibial erosion under bursitis. Pigmented villonodular synovitis with hemosiderin deposits can occur focally in the bursae.
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Location of pes anserinus bursa on medial knee. MCL = medial collateral ligament.
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Pes anserinus bursa is located on proximomedial aspect of tibia between superficial medial (tibial) collateral ligament and hamstring tendons (ie, sartorius, gracilis, and semitendinosus). This bursa serves as space where motion occurs between these hamstring tendons and underlying superficial tibial collateral ligament.
