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Pes Anserinus Bursitis: Differential Diagnoses & Workup

Author: P Mark Glencross, MD, MPH, FACOEM, FAAPMR, Occupational and Environmental Medicine, Physical Medicine and Rehabilitation, President of Florida Occupational and Environmental Medicine Consultants (FOEMC)
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Updated: Sep 10, 2009

Differential Diagnoses

Other Problems to Be Considered

• MCL sprain can be excluded by physical examination or, if necessary, by MRI.
• Medial meniscus injury presents with medial joint line tenderness, knee locking, and/or catching. The McMurray test is positive with valgus stress and external tibial rotation. In older patients, a degenerative medial meniscus may present with the insidious onset of medial knee pain.
• Discoid medial meniscus synovial plica syndrome (medial plica) can result in point tenderness and palpable clicking over the medial femoral condyle.
• Parameniscal cysts and dissecting synovial cyst (from another location) can cause swelling in the area.
• Medial ligament syndrome is a poorly defined syndrome described in rheumatology literature as causing pain at the site of insertion of the MCL. Valgus stress exacerbates pain, and the patient may have pain behaviors. The etiology is unknown, but, in some cases, an inflammatory arthropathy, such as ankylosing spondylitis, is present. Medial ligament syndrome is treated with rest, heat, and a small corticosteroid injection.
• Tumors in the region can include villonodular synovitis, osteochondromatosis, and synovial sarcoma.^5,6 Synovial hemangioma, meniscal cyst, xanthomas, and ganglion cyst also may occur here.
• Degenerative and chronic arthritis frequently involve medial knee structures and are associated with the above-described development of pes anserine bursitis. Inflammatory arthritis, such as gout and chondrocalcinosis, as well as septic arthritis, also can be associated with medial knee pain.
• Of the more than 150 bursae in the body, at least 12 of them are found in each knee, including the suprapatellar, prepatellar, infrapatellar, adventitious cutaneous, gastrocnemius, semimembranosus, sartorius, anserine, and MCL bursae, as well as 3 lateral knee bursae located adjacent to the fibular collateral ligament and the popliteus tendon (laterally).
  • The prepatellar bursa overlies the anterior portion of the patella and can become involved with kneeling and leaning forward (housemaid's knee).
  • The superficial infrapatellar bursa lies between the skin and the infrapatellar tendon; bursitis here is caused by kneeling or by a direct blow.
  • Deep infrapatellar bursitis presents with fluctuance and swelling that obliterate the depression on each side of the patellar tendon overlying the tibial tuberosity. Loss of full flexion and extension generally is observed.
  • The adventitious cutaneous bursa may be palpable as a swelling over the tibial tuberosity (adventitial bursae are those formed later in life through degeneration and do not have an endothelial lining).
  • Baker cysts arise from the gastrocnemius and/or semimembranosus bursa in the posterior knee.⁷ The gastrocnemius bursa lies between the medial head of the gastrocnemius and the joint capsule and communicates with the knee joint. The semimembranosus muscle sends tendon insertions to the posteromedial tibia behind the MCL, and a direct head inserts more posterior and distal as well. These insertions are superior and posterior to the insertion of the conjoined pes anserine tendons and the pes anserine bursa.
  • The MCL bursa (sometimes called the no-name, no-fame bursa) is located at the anterior border of the MCL. This bursa may be palpable during knee flexion as a small, tender, rounded nodule moving into the leading edge of the MCL. Pain can be elicited on palpation of the bursa or by briskly extending the knee from a position of 90° flexion. Pes anserinus tendonitis may exist exclusively or in conjunction with bursitis. So-called snapping tendinitis of the semitendinosus tendon is usually thought of as distinct from pes anserine bursitis, but some authorities classify it as the same inflammatory disorder.
• Semimembranosus tendinitis can occur with running or cutting activities. This condition is characterized by swelling over the posteromedial aspect of the knee and by tenderness with resisted flexion or valgus strain. An insertional enthesopathy of the semimembranosus muscle also has been described.
• Panniculitis in the medial knee may occur in obese individuals. As in bursitis, the pain can worsen at night.
• Stress fractures of the proximal medial tibia may produce pain in the area of the pes anserine bursa.
• Osteonecrosis (death of subchondral bone due to an unknown cause) of the femur may present with sudden, severe medial compartment knee pain that is constant (day and night). Bone scanning shows increased uptake in the femoral condyle.
• Osgood-Schlatter disease is an osteochondrosis involving traction apophysitis over the tibial tubercle in adolescent males.
• Sinding-Larsen-Johansson syndrome is a traction apophysitis at the patella's junction with the patellar tendon.
• Nerve injuries causing medial joint pain include trauma to the saphenous nerve or injury during knee surgery, especially arthroscopy. Pain can be reproduced with Tinel sign. One case report documents distal tibial pain from entrapment of the saphenous nerve caused by pes anserine bursitis.⁸ Medial knee pain associated with back pain also could represent an L3-L4 radiculopathy. Electrodiagnostic tests, such as electromyography (EMG) and nerve conduction velocity tests, may be useful.
• Fibromyalgia has characteristic tender areas or trigger points, one of which includes the medial aspect of the knee.

Workup

Laboratory Studies

• The diagnosis of pes anserinus 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 rare cases in which infection is suggested, perform a complete blood cell (CBC) count and determine the erythrocyte sedimentation rate (ESR). If the bursa or joint is aspirated for this or other reasons, analysis of the fluid may include cell count, fluid appearance, Gram stain, culture, and polarized light microscopy.
• If other pathology is suggested, consider radiography, radionuclide bone scanning, ESR determination, rheumatoid factor values, or other rheumatologic testing.

Imaging Studies

• As a rule, radiography of the knee is not indicated for bursitis. Arthritis may be observed in older adults. In rare cases, young, athletic patients have an exostosis in the metaphyseal area.
• Ultrasonography can aid the physician in the diagnosis of pes anserine bursitis.^9,10 Large, cystic bursal swellings have been evidenced by ultrasonography and by computed tomography (CT) scanning. However, published reports have described a lack of ultrasonographic findings in most suspected cases.¹¹ See Special Concerns for more discussion.
• MRI is the preferred imaging technique to help the clinician confirm the diagnosis.^12,13
  • With MRI, the pes anserine bursa is observed between the pes anserinus (ie, the gracilis, semitendinosus, and sartorius tendons) and the upper tibial metaphysis. Axial imaging is important to differentiate the bursa from other medial fluid collections.
• 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.
• 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.
• 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.

Procedures

• Aspiration of the bursa usually is not required.

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