# Diagnosis of knee joint invasion in patients with osteosarcoma: the value of direct and indirect MRI findings

## TL;DR

This study shows how MRI can help determine if osteosarcoma has spread to the knee joint, using specific imaging signs to guide treatment decisions.

## Contribution

The study identifies specific MRI findings that reliably predict joint invasion in osteosarcoma patients, improving preoperative assessment.

## Key findings

- Direct visualization of capsular insertion invasion and intraarticular bone destruction were the best predictors of joint invasion.
- Intrasynovial tumor tissue and cartilage destruction showed high specificity but lower sensitivity for joint invasion.
- Indirect signs like synovial effusion had high sensitivity but lacked specificity.

## Abstract

Osteosarcoma is the most common primary malignant bone tumor in adolescents, and the evaluation of joint invasion with MRI is important for treatment planning. This study aimed to investigate the diagnostic value of MRI findings (direct and indirect) for joint invasion in patients diagnosed with osteosarcoma of the knee region.

The MRI evaluations of 50 knee osteosarcoma patients who underwent surgical resection between 2006 and 2018 were reviewed retrospectively by two radiologists and an orthopedic oncologist. The presence of intrasynovial tumor tissue, intra-articular destruction of cartilage or bone, and invasion of the capsular and cruciate ligament insertions were evaluated as direct findings in the diagnosis of joint invasion on MRI. Indirect findings included tumor size, adjacent epiphyseal bone signal changes- bone marrow infiltration and edema, synovial contrast enhancement, and joint effusion. These findings were scored separately on a 5-point Likert scale and statistically compared with histopathologic results

The mean age of the patients was 22 years and the gender distribution was 21 females and 29 males. The best predictors for joint invasion were direct visualization of capsular insertion invasion (p < 0.05) and destruction of intraarticular bone (p < 0.05). MRI findings with statistically significant sensitivity and specificity: intrasynovial tumor tissue specificity 76%, sensitivity 58%; intra-articular cartilage destruction specificity 84%, sensitivity 56%; intra-articular bone destruction sensitivity 84%, specificity 48%; capsular insertion invasion sensitivity 92%, specificity 48%. Synovial effusion and contrast enhancement were the most sensitive indirect signs but lacked specificity.

Joint invasion by osteosarcoma can reliably be assessed on preoperative MR images with high sensitivity and specificity. Particularly direct visualization of intrasynovial tumor tissue, capsular insertion invasion, and destruction of intraarticular bone and cartilage, a combination of highly specific direct signs was valuable, while indirect signs were less predictive and specific.