Bone Case 10 Answers

1) Describe the abnormalities

There is markedly raised uptake in the sacrum, in a predominantly butterfly or H-shaped pattern, particularly on the posterior views. There is focally raised uptake in the right inferior pubic ramus. The lumbar spine shows mildly raised uptake at L2/3 disc and abnormal bony contours around the intervertebral disc spaces

2) What is the underlying diagnosis?

Osteoporotic sacral insufficiency fracture with a further fracture through the pubic ramus. Pubic rami fractures are strongly associated with sacral insufficiency fractures due to increased anterior pelvis arch strain due to failure of the stronger posterior arch. Stress fractures in patients with osteoporosis may also involve the symphysis pubis and supra-acetabular region.

The uptake in the lumbar spine is typical of degenerative change.

3) Is there an eponym here?

This is often called the "Honda sign" after the H-shaped logo of the Japanese motor company. Mostly the fractures are a combination of vertical fractures that pass through the foramina in the sacral ala parallel to the sacroiliac joints combined with a horizontal fracture through the body of the sacrum. Occasionally, it may be asymmetric - the vertical fracture may be unilateral or there is just the horizontal component. Horizontal linear dot patterns may be seen.

On dynamic bone scintigraphy, hyperaemia may be observed in the first two phases during the first 2-3 weeks after which, it gradually diminishes. Delayed static imaging remains abnormal for much longer. While some lesions resolve in approximately 6 months, it is not uncommon for lesions to be scintigraphically detectable even after 1 year, though the intensity and size of the lesion gradually diminish.

4) Can you explain the plain film findings?

Conventional radiographs in the acute setting are often unremarkable and an awareness of insufficiency fractures within the pelvis and sacrum are necessary to avoid missing these injuries. These injuries may occur without injury in the severely osteopaenic patient and the patient may have a confusing history of prior malignancy.

More than 80% of stress fractures will not be evident on initial radiographs. Also, fractures of the flat bones are trickier to diagnose on plain films (i.e. pubic rami fractures are often minimally displaced). In addition, the sacrum is particularly difficult to image on plain films due to the overlying bowel gas and its curved surfaces. To add to these difficulties, when there is advanced demineralization, the cortex and trabeculae are very thin and therefore the normal radiographic features of a fracture may not be present.

So to diagnose a fracture in demineralized sacrum is pretty difficult unless it is a grossly displaced or it is an old or healing injury where there is bone sclerosis +/- callus.

Bone scintigraphy is the investigation of choice in this setting. It is readily available, its sensitivity for the diagnosis of stress fracture approaches 100%, and has the advantage of looking at the entire skeleton for associated insufficiency fractures. Normally, 80% of bone scintigraphy will show increased activity at a site of fracture by 24 hours, and 95% by 72 hours, although older (over 75 y) and debilitated patients may not show activity for several days to as much as 2 weeks.

Alternative imaging methods include CT which shows the bony margins more clearly and also certain sequences (e.g. STIR) on MRI are very sensitive for the oedema associated with a fracture.

Return to question

Return to home page

The text is entirely the opinion of the author and does not necessarily reflect that of RUH NHS Trust or the Bristol Radiology Training Scheme. Website content devised by Paul McCoubrie.