Baker's Cyst in Rheumatoid Arthritis: A Musculoskeletal Ultrasound Study

Objectives: To investigate the frequency of Baker's cysts in rheumatoid arthritis (RA). Methods: We retrospectively analyzed the clinical and musculoskeletal ultrasound (MUS) findings of 150 patients diagnosed with RA according to the American College of Rheumatology revised criteria. We used logistic regression to analyze the relationship between (1) patient age and incidence of Baker's cyst and (2) diameter of the cyst and incidence of rupture. In addition, we used analysis of variance (ANOVA) to analyze the relationship between knee effusion grading and the diameter of the Baker's cyst. Results: Baker's cyst was detected in 39 patients with RA (26%) and in 48 of the 300 examined knees (16%). Eleven of the 48 cysts ruptured. Age was not correlated with the incidence of Baker's cyst (p = 0.4554), and cyst diameter was not correlated with the incidence of rupture (p = 0.3910). Knee effusion grading was not correlated with cyst diameter (p = 0.5342). Conclusion: Although Baker's cyst is common in RA, it is not easy to diagnose. Ultrasound should be widely employed to diagnose Baker's cyst. Furthermore, clinicians should be alert in identifying this common complication of RA, which may be accompanied by considerable morbidity.