Knee MRI Features Associated with Baker Cyst Presence and Size: Anatomical, Degenerative, and Synovial Factors.

Abstract

Purpose: To comprehensively evaluate anatomical, degenerative, and synovial factors associated with Baker cyst presence and volume on knee MRI.

Materials and methods: This retrospective study included 219 patients who underwent knee MRI between January 2025 and December 2025 (119 with Baker cysts, 100 controls). Recorded variables included medial femoral condyle dimensions (distal and posterior articular diameters, width, length), patellofemoral/trochlear morphology, degenerative findings, effusion grade, the arrangement pattern between the medial head of the gastrocnemius and the semimembranosus tendon and Baker cyst volume. Group comparisons and multivariable logistic and log-linear models were performed.

Results: Patients with cysts had a significantly smaller posterior articular diameter of the medial condyle than the controls (median 29.8 vs. 32.5 mm, p<0.001), the strongest anatomical discriminator among condylar metrics. Meniscal degeneration, meniscal tear, and anterior cruciate ligament mucoid degeneration showed significant association with cyst presence. Cyst volume correlated positively with effusion (ρ=0.38, p<0.001), medial condyle size parameters, and degenerative findings. Tendon arrangement morphology showed an ordinal trend with volume (concave→flat→convex). In multivariable analysis for cyst presence, the posterior articular diameter of the medial condyle remained an independent anatomical predictor. However, in the log-linear model for cyst volume, effusion emerged as the strongest determinant, with each grade increase associated with a 54% enlargement. The final multivariable model demonstrated good to excellent discrimination for predicting cyst presence (AUC=0.80-0.81).

Conclusion: Baker cyst presence is linked to meniscal and ligament degeneration with additional anatomical features, particularly reduced posterior articular diameter of the medial condyle, while cyst enlargement is primarily associated with effusion and tendon arrangement.

Key points: · Baker cyst presence was independently associated with reduced posterior articular diameter of the medial femoral condyle and degenerative knee findings.. · Cyst volume was mainly associated with effusion, with contributions from condylar morphology and tendon arrangement, highlighting distinct predictors of cyst presence and enlargement..

Citation format: · Ozen Atalay H, Timocin Yigman G, Dokuyucu EE. Knee MRI Features Associated with Baker Cyst Presence and Size: Anatomical, Degenerative, and Synovial Factors. Rofo 2026; DOI 10.1055/a-2942-7551.