Correlation between post-chemotherapy MRI and histopathology of malignant bone tumors treated with extra-articular resection.

Objective: Magnetic resonance imaging (MRI) remains the gold standard for diagnosing tumoral joint involvement; however, its interpretation remains uncertain due to the presence of perilesional edema that can lead to unjustified arthrectomy. The aim of the study is to identify precise MRI signs that are predictive of joint involvement.

Materials and methods: This retrospective multicenter study included 25 patients who underwent extra-articular resection for malignant bone tumor with suspected joint involvement at the shoulder, hip, or knee, between January 2004 and July 2023. Joint resection was indicated based on preoperative MRI examination. MRI signs of joint involvement were joint effusion, capsuloligamentous invasion, disruption of articular cartilage, and intra-articular tumor mass. We then compared histopathological "true" joint involvement of the resected specimen with its preoperative MRI diagnosis.

Results: Extra-articular resection was performed in 9 shoulders, 4 hips, and 12 knees. Histological analysis confirmed wide resections for all patients. Based on histopathological analysis, extra-articular resection was unjustified in 40% (44%, 0%, and 50%, respectively). The most specific iconographic criteria were intra-capsular cortical breach and the presence of a tumor mass inside the joint. Articular cartilage disruption is often the most accurate sign.

Conclusion: Our results suggest that MRI has a poor ability to accurately diagnose joint involvement. To date, however, this is the best tool available. In addition to obvious signs of joint involvement, MRI analysis must be performed with a thorough understanding of capsular anatomy and its particularities for each joint so as not to miss other signs, such as intra-capsular cortical effraction.