Diagnostic Considerations
In addition to the conditions listed in the differential diagnosis, other problems to be considered include the following:
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Medial meniscal tear
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Spontaneous osteonecrosis
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Tumors
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Other bursitis of the knee
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Proximal tibia stress/fracture
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Saphenous nerve compression
Medial collateral ligament (MCL) sprain can be excluded by means of physical examination or, if necessary, magnetic resonance imaging (MRI).
Medial meniscus injury presents with medial joint line tenderness, knee locking, 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. Medial 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.
Medial tibial condyle bone marrow edema associated with soft tissue edema surrounding the MCL on MRI has been reported to result in a painful syndrome of medial tibial crest friction, possibly related to the angle of the crest. [25] This is not to be confused with medial tibial stress syndrome, "shin splints," which is pain in the mid-to-distal tibia.
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.
Tumors in the region can include villonodular synovitis, osteochondromatosis, and synovial sarcoma. [26, 27, 28] Synovial hemangioma, meniscal cyst, xanthomas, and ganglion cyst also may occur here.
Of the more than 150 bursae in the body, at least 12 of them are found in each knee, including the suprapatellar, prepatellar, deep 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). Knee pain may be the consequence of inflammation of any of these bursae.
The MCL bursa is located at the anterior border of the MCL. It may be palpable during knee flexion as a small, tender, rounded nodule moving into the leading edge of the MCL. Pain can be elicited by palpating the bursa or by briskly extending the knee from a position of 90° flexion. Pes anserine 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 has also been described.
Stress fractures of the proximal medial tibia may produce pain in the area of the pes anserine bursa.
Nerve injuries causing medial joint pain include trauma to the infrapatellar branch of the saphenous nerve and injury during knee surgery, especially arthroscopy. Pain can be reproduced with the Tinel sign. One case report documents distal tibial pain from entrapment of the saphenous nerve caused by pes anserine bursitis. [29] 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.
Differential Diagnoses
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Osgood-Schlatter Disease
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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.
