Structural factors associated with Baker's cyst volume in degenerative knees: A large MRI-based cohort study

PurposeTo evaluate structural factors associated with Baker's cyst volume and determine whether cyst enlargement is related to medial meniscus posterior root tear (MMPRT), medial meniscus extrusion (MME), posterior tibial slope (PTS), and radiographic osteoarthritis severity.MethodsThis retrospective study included 876 knee MRI examinations with MRI-confirmed Baker's cysts after predefined exclusions. Baker's cyst volume, MMPRT status, MME, PTS, and Kellgren-Lawrence osteoarthritis grade were assessed using standardized imaging protocols. Factors associated with cyst volume were evaluated using multivariable linear regression. Logistic regression and receiver operating characteristic analysis were performed to assess the relationship between cyst volume and MMPRT. Measurement reliability was evaluated using intraclass correlation coefficients.ResultsMMPRT was independently associated with larger Baker's cyst volume (p = 0.004). Greater PTS was also associated with increased cyst volume, with each 1° increase corresponding to a significant volume increase (p = 0.012). Increasing Kellgren-Lawrence grade remained independently associated with larger cyst volume (p < 0.001), and MME showed an independent but modest association (p = 0.044). The final regression model was significant (F (8,867) = 23.45, p < 0.001) and explained 17.8% of the variance. ROC analysis identified 10.16 cm³ as the optimal cyst volume threshold for identifying MMPRT; however, discriminative performance was modest, indicating that cyst volume should not be interpreted as a standalone diagnostic marker. ICC values ranged from 0.79 to 0.91.ConclusionBaker's cyst enlargement is associated with MMPRT, increased PTS, greater MME, and increasing osteoarthritis severity. Larger cysts may prompt careful evaluation of the medial meniscus posterior root and degenerative joint burden on routine knee MRI, but cyst volume should be interpreted together with other structural imaging findings.