[The value of MRI in the diagnosis of joint involvement in malignant primitive tumors of the knee].

Introduction: Surgical treatment of malignant primitive tumors of bone needs a precise preoperative assessment of tumor local extension. Joint involvement (JI) represents the most important finding to determine, for the choice of surgical procedure (intra- or extra-articular resection).

Objective: To determine the value of different MR signs for the diagnosis of joint involvement in malignant primitive tumors of the knee.

Methods: Ten-year period retrospective study of 42 patients. Patients' clinical and imaging data have been studied. Two senior musculoskeletal radiologists have blindly and consensually reviewed imaging data. Histopathological data have been reviewed by an experimented pathologist. The results have been compared using several statistical methods to determine the global and detailed (sign by sign) diagnostic value and accuracy of MRI by reference to histopathology.

Results: Some MR signs were performant in the diagnosis of joint involvement. The most sensitive were epiphyseal extension (Se: 100%), osteochondral extension (Se: 87.5%) and extension to the tibial spines (Se: 83.3%). The most specific MR signs were the presence of an intra-articular mass (Sp: 84.62%), extension to the intercondylar notch (Sp: 80.77%) and longitudinal axis≥120mm (Sp: 84.62%).

Conclusion: A rigorous and reproducible MR technique has to be used, the knee being explored in the transversal, sagittal and coronal planes. MR conclusion has to be clear and simple (intact, doubtful or involved joint). MR interpretation has to consider tumoral extension pathways. In doubtful cases, CT may help in this diagnosis by studying the bone cortex.

Level Of Evidence: IV.