Assessment of Imaging Factors Associated with Baker’s Cyst Rupture on Knee MRI

OBJECTIVES: To identify the factors associated with Baker’s cyst rupture on MRI. MATERIAL AND METHODS: From January 2021 to December 2022, a total of 441 knee MRI examinations in 441 patients (mean age: 47.7 ± 13.8 years) with Baker’s cyst were included in this study. Patients were classified into two groups: those with ruptured vs. unruptured Baker’s cysts. On knee radiograph, osteoarthritis grade was assessed based on Kellgren-Lawrence grade. On MRI, combined structure injuries, alignment type between semimembranosus tendon and medial head of gastrocnemius tendon, amount of joint effusion, presence of septation, maximal diameters of cyst, and cyst volume were evaluated. Receiver operating characteristic (ROC) analysis was performed to assess the predictive performances of imaging factors for cyst rupture. RESULTS: There were 146 patients with Baker’s cyst rupture and 295 patients without rupture. Patients with cyst rupture showed significantly longer maximal transverse diameter (25.8 ± 6.8 mm vs. 21.6 ± 5.8 mm, p = 0.035) and larger volume (13.3 ± 6.2 cm(3) vs. 9.9 ± 5.1 cm(3), p = 0.012) than those without rupture. On ROC analysis, maximal transverse diameter of cyst ≥ 22.2 mm (sensitivity = 64.4%, specificity = 54.9%) and cyst volume ≥ 10.9 cm(3) (sensitivity = 71.2%, specificity = 58.3%) were the cutoff values for predicting rupture of cyst, respectively. The cyst volume showed significantly higher area under the curve (AUC) than maximal transverse diameter (0.726 vs. 0.642, p = 0.002). CONCLUSION: Longer transverse diameter and larger volume of Baker’s cyst could be predictive imaging parameters for cyst rupture.