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Insufficiency fractures are a type of stress fracture, which are the result of normal stresses on abnormal bone. Looser zones are also a type of insufficiency fracture. They should not be confused with fatigue fractures which are due to abnormal stresses on normal bone, or with pathological fractures, the result of diseased, weakened bone due to focal pathology such as tumors (both malignant and benign).
In general, they are seen in the elderly, more frequently in women 2.
They are most often seen in the setting of osteoporosis, although any process which weakens bone is a risk factor. Long-term bisphosphonate use has also been associated with insufficiency fractures 5.
Osteoporosis is the most common cause of insufficiency fractures, although there are many causes 7-9:
medications: glucocorticoids, chemotherapy
vertebral (crush or wedge) fractures: very common
marrow edema is limited to the vertebral body; extension of abnormal signal into the pedicles suggests an underlying lesion
sacrum: Honda sign
proximal third femur (see article: bisphosphonate-related proximal femur fractures) 5
Early diagnosis is best made with a bone scan or MRI, as plain films may initially appear normal.
periosteal reaction progressing to callus formation in diaphyseal fractures
linear sclerosis and cortical thickening more frequent in metaphyseal and epiphyseal fractures 2
MRI is as sensitive as bone scanning, with the added benefit of higher specificity, both in isolating the exact anatomic location and in distinguishing fractures from tumors or infection.
T1: low marrow signal
T2: high marrow signal with extension into adjacent soft tissues
T1 C+ (Gd): enhancement can be intense
On bone scan, there is increased activity at the site of the fracture.
Treatment and prognosis
Treatment of the underlying cause of bone weakness is also essential.