The Honda Sign on Bone Scan
The Honda sign — also called the butterfly or H sign — is a characteristic pattern of increased tracer uptake in the sacrum on bone scan, seen in a sacral insufficiency fracture. It is increased activity in both sacral ala, the two vertical limbs, joined by a horizontal component across the sacral body, resembling the letter H or the Honda car logo.
Underlying pathology
- Bilateral vertical sacral ala fractures with a transverse component.
- Insufficiency fractures — weakened bone failing under normal stress.
Typical clinical context
- Postmenopausal osteoporosis — the commonest setting.
- Prior pelvic radiotherapy.
- Long-term corticosteroid therapy; rheumatoid arthritis; renal osteodystrophy.
Why it matters
- It explains low back or buttock pain that may otherwise be mistaken for metastasis, and spares the patient an unnecessary work-up.
- Bone scan, with SPECT/CT where available, is very sensitive and may be positive before radiographs.
- The complete H is not always present — partial patterns occur.
Fuller version, with the rest of benign bone disease: Metabolic & benign bone disease.
Take home
- An H or butterfly of sacral uptake is a sacral insufficiency fracture, not metastasis.
- Look for it in postmenopausal osteoporosis, after pelvic radiotherapy, and on long-term corticosteroids.
- A partial pattern still counts — the complete H is often absent, and the scan may be positive before radiographs.
Sources
- Ries T. Detection of osteoporotic sacral fractures with radionuclides. Radiology. 1983;146(3):783-5.
- Lyders EM, Whitlow CT, Baker MD, Morris PP. Imaging and treatment of sacral insufficiency fractures. AJNR Am J Neuroradiol. 2010;31(2):201-10.
- Van den Wyngaert T, Strobel K, Kampen WU, et al. The EANM practice guidelines for bone scintigraphy. Eur J Nucl Med Mol Imaging. 2016;43(9):1723-38.