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Scientific Session 10 — Musculoskeletal - Knee and Shoulder

Tuesday, May 2, 2017

Abstracts 1147-3271

2585. Differentiation of Insufficiency Fractures and Leaking Baker Cysts by Soft Tissue Edema Patterns

Lawyer A1*,  Shabshin N1,2,  Schwartz N2,  Beer Y3 1. University of Pennsylvania, Philadelphia, PA; 2. Emek Medical Center, Afula, Israel; 3. Assaf Harofeh Medical Center, Tzrifin, Israel

Address correspondence to A. Lawyer (

Objective: Posterior soft-tissue edema about the knee is often related to a leaking Baker cyst. Recently, a soft-tissue pattern was described in spontaneous insufficiency fracture of the knee (SIFK). During our clinical work, we have observed several cases in which posterior soft-tissue edema preceded the development of SIFK. This observation motivated us to investigate and compare the patterns of soft-tissue edema noted in these two conditions.

Materials and Methods: The 3-T and 1.5-T MR images of 88 patients (mean age, 55.4 years; age range, 45–64 years) with SIFK or leaking Baker cyst were retrospectively evaluated by two observers for the following soft-tissue edema patterns: extending proximal to the MCL along the femur, extending into the vastus medialis or lateralis, extending distal to the joint along the gastrocnemius muscles, and extension of edema proximal versus distal to the gastrocnemius insertion. Patterns were analyzed and compared between both conditions using the chi-square test.

Results: Patterns associated with SIFK included edema extending proximal to the MCL (p < 0.0001; positive predictive value [PPV], 79.31%, negative predictive value [NPV], 88.14%), edema involving vastus medialis or lateralis (p < 0.0001), and edema proximal to the gastrocnemius insertion (p < 0.0001; PPV, 86.97%; NPV, 92.59%). The pattern associated with a leaking Baker cyst was edema extending distal to the knee along the gastrocnemius muscle (p < 0.0001; PPV, 80.65%; NPV, 91.23%). Joint synovitis was present in 16/30 (53%) cases of SIFK and in 29/58 (50%) cases of leaking Baker cyst. There were no sex or age differences among conditions.

Conclusion: Different posterior soft-tissue edema patterns are identifiable in patients with SIFK and a leaking Baker cyst. Edema extending along the femur proximal to the MCL, proximal to the gastrocnemius origin, and into the vastus muscles is highly indicative of SIFK. Edema extending distally along the gastrocnemius is highly indicative of a leaking Baker cyst. Our work demonstrates that SIFK and leaking Baker cyst demonstrate characteristic posterior soft-tissue edema patterns on MRI. Knowledge of these patterns may lead to an early diagnosis of SIFK, even before bone marrow edema occurs.