Medial collateral ligament (MCL) bursitis has been described as a distended and inflamed bursa between the superficial and deep portions of the MCL. It is a rare but important cause of medial knee pain.
A 65-year-old woman with knee osteoarthritis (OA) presented with severe pain and swelling in her left knee. She did not have a traumatic injury. 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. The magnetic resonance (MR) imaging showed a distended bursa with internal septations beneath the superficial portion of the MCL. MCL bursitis was considered as diagnosis and an ultrasound-guided corticosteroid injection into the bursa was performed.
There was a significant improvement in pain intensity in the follow-up examination. A repeated MR imaging 2 months later showed a marked improvement, and approximation of the deep and superficial portions of the MCL.
MCL bursitis, which is a rare condition, must 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.