Osteoblastoma crossing the sacro-iliac joint.

Osteoblastoma is a rare primary bone tumour which is well-described in the spine and sacrum. We report a case of histologically confirmed osteoblastoma in a 20-year-old male which crossed the sacroiliac joint. This has not previously been described to our knowledge. The imaging features of osteoblastoma and sacroiliac joint involvement by bone tumours are reviewed.