Transarticular invasion of bone tumours across the sacroiliac joint.

Purpose: The purpose of this study was to evaluate the pattern of tumour spread across the SI articulation, correlating with cadaveric anatomic observations, in order to better understand the local spread of tumour and to assist in the assessment of local staging.

Material And Methods: Twenty-four consecutive patients (14 male, 10 female; age range 22-89 years, mean 52 years) with primary bone tumours of the iliac bone or sacrum abutting the SI joint, in whom surgical resection of the SI joint was performed, were studied following institutional ethics approval. In all patients, preoperative magnetic resonance (MR) imaging studies of the pelvis and SI joint were reviewed for imaging evidence of transarticular extension across the SI joint. Gross pathologic and histologic assessment of possible transarticular SI joint tumour extension was performed in all patients. Nine cadaveric pelvic specimens without pelvic neoplastic disease (4 male, 5 female; age range 20-84 years, mean 59 years, median 58 years) were anatomically dissected and the articular anatomy of the SI joint examined macroscopically.

Results: Twelve of the twenty-four patients demonstrated imaging and histological evidence of transarticular SI joint invasion. Eight tumours infiltrated only the interosseous ligamentous aspect of the SI joint. In the remaining four cases, extensive tumour infiltrated both the cartilaginous and ligamentous aspects of the joint. No case showed tumour involvement isolated to the cartilaginous aspect of the joint. Among the cadaveric specimens studied, degenerative changes were found involving the majority of cases (6/9), with cartilage thinning and fibrillation and antero-superior marginal osteophytes seen involving the cartilaginous portion of the SI joint articulation. Four of the nine specimens demonstrated central ossification bridging the iliac and sacral aspects of the ligamentous (interosseous) SI joint.

Conclusion: Tumour invasion across the SI articulation favours its interosseous ligamentous portion. Factors influencing transarticular tumour extension and its preferential course across the interosseous component of the articulation have been discussed. It is particularly important to assess the interosseous ligamentous portion of the SI articulation when locally staging primary pelvic bone tumours subjacent to the SI articulation, as this will have a significant impact on planning surgical management.