Medial collateral ligament bursitis in a patient with knee osteoarthritis

1. Introduction

Bursae are typically thin cushions located between bony surfaces and surrounding soft tissues like ligaments and tendons where friction occurs. There are several bursae located around the knee such as prep-atellar or pes anserinus that cause symptoms when inflamed. These are well known and generally treated [1].

Medial collateral ligament (MCL) bursa was first defined by Brantigan and Voshell in 1943 as a presence of a bursa deep to the MCL and five different locations were described where it could be found [2]. The clinical condition was reported as MCL bursitis when the bursa is inflamed and distended by fluid. In 1988, Kerlan and Glousman described the clinical criteria of MCL bursitis as tenderness over the MCL at the joint line without a history of mechanical symptoms based on their findings of patients [3]. Later a few reports of MCL bursitis in sport medicine have been documented and a sonographically guided therapeutic injection of MCL bursitis has been described [4, 5, 6].

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In a study assessing MR imaging of MCL bursa, fluid in the MCL bursa was found in six out of 2454 MR examinations after excluding MR imaging findings of MCL and meniscus tears. In three of them it was reported as the single finding, and the other patients had an adjacent medial knee osteoarthritis (OA) [7]. Although MCL bursitis is rarely seen, it is an important cause of medial knee pain and should be differentiated from other common conditions that cause medial knee pain.

In this article, we report a patient with knee OA who had knee pain for many years and suffered from increasing medial knee pain because of MCL bursitis and was treated successfully with a single intrabursal corticosteroid injection.

A 65-year-old woman with knee OA was admitted to the outpatient clinic with severe pain and swelling in her left knee. She explained that she had mild to moderate knee pain for many years and a history of medial meniscus tear that was arthroscopically treated twelve years before but for six months pain became severe and localized to the medial aspect of the left knee. She did not have a traumatic injury and was treated elsewhere with nonsteroidal antiinflammatory drugs with limited benefit. After a clinical examination a slight decrease in the range of motion of the left knee, and a painful swelling and tenderness over the medial side of the knee and proximal tibia were detected. The pain was exacerbated by valgus stress test. On the other hand there was a normal medial side knee laxity in extension and 30 ∘ knee flexion. Other ligament and meniscal tests were negative. Laboratory tests were within normal range. Narrowing of the medial joint space, osteophyte formation, and soft tissue swelling were seen on plain radiographs. The magnetic resonance (MR) imaging showed a distended bursa with internal septations beneath the superficial portion of the MCL (Fig. 1a and b). MCL bursitis was considered according to clinical and radiological findings and an ultrasound-guided corticosteroid injection into the bursa was performed. There was a significant improvement in pain intensity in the follow-up examination (pre- and posttreatment visual analog scores for knee pain intensity were 9 and 3, respectively), and a repeated MR imaging 2 months later showed marked improvement and approximation of the deep and superficial portions of the MCL (Fig. 2a and b). No side effect was seen due to injection.

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Medial knee joint pain is widely seen in older adults and there are many possible etiologies such as medial compartment degenerative joint disease, medial meniscus tears, meniscus cysts, MCL tears, stress fractures, tendonitis and bursitis. The medial supporting structure of the knee can be separeted into three layers. The first layer consists of the deep crural fascia. The superficial portion of the MCL is the main component of the second layer and, the joint capsule and deep portion of the MCL which comprises the meniscotibial and meniscofemoral extensions make up the third layer [8]. MCL bursa was found to be located between the superficial and deep portions of the MCL and not identified on MR imaging in the absence of fluid collection [7].

MCL bursitis is infrequently seen but it must be kept in mind for differenteal diagnosis in patients with medial knee joint pain to avoid unnecessary artroscopic surgery that may be held in these patients for diagnosis and treatment [3]. Trauma, osteophytic spurs, rheumatic disorders, genu valgus, and flatfoot deformity have been suggested as causes of MCL bursitis [3, 9, 10]. Medial knee joint pain, a palpable swelling, and increased pain by applying valgus stress to the knee are typical clinical findings [3]. Clinical symptoms and findings along with imaging findings confirm the diagnosis. The presented patient had knee OA and osteophytes might be the cause of MCL bursitis by impinging on the MCL and leading to inflammation and distension of the MCL bursa [10]. Although there was a history of arthroscopically treated medial meniscus tear before, clinical findings like tender swelling and severe pain localized to the medial aspect of the knee which was aggravated with valgus stress test, imaging findings, and benefiting from a single injection of intrabursal corticosteroid, confirmed the diagnosis as MCL bursitis.

In conclusion, although it is a rarely seen condition, MCL bursitis should be considered for the differential diagnosis of increased medial knee pain in patients with knee OA. Corticosteroid injection is an effective and safe treatment modality for the management.