Sacral insufficiency fractures are a subtype of stress fractures, which are the result of normal stresses on abnormal bone, most frequently seen in the setting of osteoporosis. They fall under the broader group of pelvic insufficiency fractures.

Epidemiology

Risk factors

Risk factors are those of osteoporosis as well as other abnormal bone conditions, including ⁶:

• osteoporosis: most common

• rheumatoid arthritis

• Paget disease

• osteomalacia: Milkman syndrome

• diabetes mellitus

• history of radiation therapy

Associations

Long-term bisphosphonate use has been associated with insufficiency fractures. 

Clinical presentation

They are usually seen in elderly females who present with low back pain without any history of significant trauma.

Pathology

They are most frequently seen in the setting of osteoporosis, although any process which weakens bone is a risk factor. 

Radiographic features

Plain radiograph

They may be normal, or a sclerotic line may be noted in the involved region(s).

CT

May show a fracture line along with sclerosis that is parallel to the sacroiliac joint, although even CT imaging is less sensitive as compared to MRI and nuclear imaging.

MRI

Can depict bone marrow oedema as early as 18 days after the development of symptoms.

Nuclear medicine

Uptake of Tc-99m MDP is also sensitive but not specific. A typical H-sign or Honda sign (uptake in H pattern) may be noted in 20-40% of cases and is considered diagnostic.

Treatment and prognosis

Treatment options can be variable ranging from conservative management to sacroplasty ⁵.