The etiology and clinical manifestation of Baker's cyst: a musculoskeletal ultrasound study

Purpose: Patients with rheumatic disease have a higher risk of developing Baker's cysts. The aim of this study is to determine the etiology of a Baker's cyst and clinical manifestation. Method and Material: This is a retrospective review study using the musculoskeletal ultrasonography (MUS) database from June 2006 to June 2010. The relationship between the etiology of a Baker's cyst and its clinical manifestation, including gender, size of cyst, symptoms, physical examination, and complication, were analyzed using Pearson correlation coefficient, Student's t test, one-way ANOVA and multiple logistic regression. Results: We identified 301 Baker's cysts in 257 patients. The prevalence of bilateral cysts was 5.9-27.3% across its different etiologies. We found that the most common cause of Baker's cyst was osteoarthritis (53.5%), while the most common cause of a ruptured Baker's cyst was Rheumatoid Arthritis (RA) in women (47%) and gout in men (35%). Both grading of effusion and Kellgren and Lawrence(KL) grade were positive related to the size of a Baker's cyst. The mean size of palpable cyst was 7.95±0.53 cm and that of non-palpable cyst was 2.65±0.11 cm (p＜0.001). The size of Baker's cyst (cm) was correlated with cyst rupture with odds ratio (OR): 2.58, confidence interval (CI): 1.69-3.95 (p＜0.001). Conclusion: The etiology of a Baker's cyst was different between the sexes. For early detection, MUS should be performed in patients with advanced KL grade or knee effusions. In addition, patients with a Baker's cyst on one knee, an imaging study should be performed on the contralateral side.目的：風濕性疾病患者得到貝克氏囊腫的風險較高。這項研究的目的是為了瞭解貝克囊腫的病因和其臨床表現之關聯性。方法：這是一項回顧性研究，使用2006年6月至2010年6月的肌肉骨骼超音波資料庫。分析了貝克氏囊腫的病因與臨床表現（包括性別，症狀，身體檢查，囊腫大小和併發症）統計資料分析使用Pearson相關係數，Student's t檢驗，one-way ANOVA和多因素回歸測試。結果：我們在257名患者中發現了301個貝克氏囊腫。不同病因造成之雙側膝蓋囊腫之患病率為5.9-27.3%。我們發現造成貝克氏囊腫最常見的原因是退化性關節炎（53.5%），而貝克氏囊腫破裂的最常見原因於女性是類風濕性關節炎（47%）於男性則是痛風（35%）。關節積液分級，Kellgren and Lawrence（KL）分級均與貝克氏囊腫大小呈正相關。可摸到的囊腫的平均大小為7.95±0.53公分，摸不到的囊腫的平均大小為2.65±0.11公分（p ＜0.001）。貝克氏囊腫的大小（公分）與囊腫破裂呈正相關，Odds Ratio為：2.58，信賴區間（CI）：1.69-3.95（p ＜0.001）結論：引發貝克氏囊腫的病因在兩性之間是不同的。骨骼肌肉超音波應用在患有較嚴重的KL grade或膝關節積液的患者有助於早期診斷貝克氏囊腫，而如果病人在一側膝蓋發現貝克氏囊腫，則應在其對側膝蓋進行影像學檢查。