Transarticular invasion of primary bone tumors abutting the sacroiliac joint: an MRI study in 128 patients
Authors: Ding Lei , Yin Jun-qiang , Zhang Fang-ling , Wang Yong-qian , Zou Chang-ye , Gao Zhenhua 
Published: September 2019

Abstract
Background: To investigate magnetic resonance imaging (MRI) manifestation of transarticular invasion of primary bone tumors abutting the sacroiliac joint and to compare the transarticular invasion incidences and transarticular routes of primary bone tumors in different locations, of different pathological types, and of different pathological grades. Methods: We conducted a retrospective analysis of clinical and MRI data for 128 patients (80 males, 48 females; mean age, 32.5 years; age range, 4-74 years) treated in our hospital from January 2004 to December 2015. The primary tumors located in the ilium in 87 patients and the sacrum in 41 patients. The diagnosis of the patients was confirmed by surgical findings and pathological examination. Based on pathology grading systems, the tumors were divided into a high-grade malignant tumor group (Group 1), low-grade malignant tumor group (Group 2) and intermediate tumor group (Group 3). Transarticular invasion routes included 3 types: invasion across the ligamentous portion (Type 1), across articular cartilage (Type 2) and across periarticular tissue (Type 3). For tumors with coexistence of multiple types of invasion, each type was counted once. Results: Transarticular invasion of primary bone tumors abutting the sacroiliac joint were diagnosed in 33 patients (25.8%). Group 1 included 15 patients (51.7%) with conventional osteosarcoma and 7 patients (43.8%) with Ewing's sarcoma. Group 2 included 4 patients (11.4%) with central chondrosarcoma and 1 patient (7.7%) with chordoma. Group 3 included 4 patients (20.0%) with giant cell tumor of bone, 1 patient (16.7%) with chondroblastoma and 1 patient (11.1%) with aneurysmal bone cyst. Transarticular invasion incidences were not significantly different between primary iliac and sacral tumors (χ2 value = 2.39, P > 0.05). Transarticular invasion incidences were not significantly different between group 2 and group 3 (χ2 value = 0.32, P > 0.05). However, the transarticular invasion incidences were significantly different between group 2 or 3 and group 1 (P < 0.01). Of the 33 patients with transarticular invasion, the invasion types included 31 type 1, 15 type 2 and 5 type 3 invasions. A significant difference was observed between different invasion types (P < 0.01). By contrast, the different invasion types were not related to different pathological grades (P > 0.05). Conclusions: MRI is a highly sensitive method to diagnose transarticular invasion of primary bone tumors abutting the sacroiliac joint. The transarticular invasion incidence is not significantly different between primary iliac and sacral tumors. Tumor invasion across the sacroiliac joint can be present in both malignant and intermediate bone tumors, but predominantly in osteosarcoma and Ewing's sarcoma. Transarticular invasion across the ligamentous portion is more common. No significant difference is evident between the 3 types of invasion in the groups with different pathological grades, suggesting that the transarticular invasion types are not related to the malignant degree of tumor.