Sacral Insufficiency Fractures

Sacral insufficiency fractures are relatively uncommon. When they occur, however, they are frequently missed. They develop in osteoporotic individuals, mostly slim elderly women, frequently without any preceding trauma or following a fall. Occasionally, bilateral fractures in the allae of the sacrum are encountered. At times, in addition to the sacral fractures the patients sustain pelvic rim fractures, especially in the pubic rami region.

Clinical Presentation

The usual presenting symptom is severe pain that is located in the low back region or proximal buttock. The pain interferes with the patient's ability to ambulate. The neurological examination remains normal. The straight-leg raising test remains negative but the patient may experience increased pain when the lower extremity is manipulated.

Imaging Studies

Plain films often do not reveal the fracture because the area is commonly obscured by bowel shadows. When the plain films are negative, bone scan and/or pelvic CT or MRI may help in establishing the diagnosis. The bone scan may show increased uptake at the fracture site (Figure 10-13). CT scan can easily detect cortical defects and may show the fracture lines, which are usually found adjacent to but not involving the sacroiliac joints. In older fractures the CT will show sclerotic bands adjacent to the sacroiliac joints (Figure 10-14). MRI can establish the correct diagnosis and help rule out metastatic disease. It will detect bony edema at the fracture site, which will appear as a hypointense region on T1WI and hyperintense on T2WI. Fat suppression may further help define the extent of the edematous area (Figure 10-15).

Management

Patients with sacral insufficiency fractures should be kept ambulatory when possible. Pain management is critical in the early stages.

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