Insufficiency Fractures¶

Definition¶

Insufficiency fractures are a type of stress fracture that occurs when normal physiological forces act on bone with decreased elastic resistance — that is, bone that is weakened by an underlying process. In the spine, insufficiency fractures most commonly affect the sacrum and vertebral bodies in patients with osteoporosis, prior radiation therapy, or metabolic bone disease.

Etiology¶

Osteoporosis — The most common cause, particularly in postmenopausal women
Radiation therapy — Pelvic or spinal radiation weakens bone, with insufficiency fractures typically occurring 2 months to several years after treatment
Corticosteroid therapy — Chronic steroid use causes osteoporosis and increases fracture risk
Metabolic bone disease — Osteomalacia, hyperparathyroidism, Paget disease, renal osteodystrophy
Rheumatoid arthritis — Both the disease and its treatment (steroids) contribute to bone weakening

Sacral Insufficiency Fractures¶

Sacral insufficiency fractures are the most common sacral fracture type in the elderly and are a frequently underdiagnosed cause of low back and buttock pain.

Classic Pattern¶

The classic pattern is bilateral vertical fractures through the sacral ala, parallel to the sacroiliac joints, sometimes connected by a horizontal fracture through the sacral body — creating the characteristic "H" pattern or "Honda sign" on bone scintigraphy (named for its resemblance to the Honda Motor Company logo).

Imaging¶

MRI — The most sensitive modality:

STIR: Bright signal in the sacral ala representing bone marrow edema — the fracture line may be visible as a low-signal line within the edema
T1: Low signal replacing normal fatty marrow

CT — May show subtle fracture lines through the sacral ala. Can be difficult to detect without a high index of suspicion, as the fracture lines are often oriented parallel to the axial plane.

Bone scintigraphy — The "H" or "Honda" sign is classic but not always present. High sensitivity but lower specificity.

Radiography — Sacral insufficiency fractures are essentially invisible on radiographs due to overlying bowel gas and the complex sacral anatomy.

Clinical Pearl

Sacral insufficiency fractures are a common cause of acute low back and buttock pain in elderly, osteoporotic patients — particularly postmenopausal women — and are frequently misdiagnosed as lumbar disc disease or SI joint dysfunction. When an elderly patient presents with acute-onset low back/buttock pain without significant trauma, MRI of the pelvis with STIR sequences should be considered. The bilateral sacral alar edema pattern on STIR is essentially diagnostic.

Vertebral Insufficiency Fractures¶

Vertebral body insufficiency fractures are synonymous with osteoporotic compression fractures in most clinical contexts. They are discussed in detail in the Thoracolumbar Compression Fracture article.

Key features:

Most common at the thoracolumbar junction (T11–L2) and mid-thoracic spine (T7–T8)
Present as anterior wedge deformity on radiographs and CT
MRI with STIR is essential for confirming acuity (bone marrow edema) and excluding malignancy
Multiple fractures may produce progressive kyphosis

Management¶

Pain management — Analgesics, physical therapy, activity modification
Treatment of underlying cause — Bisphosphonates, calcium and vitamin D supplementation, denosumab for osteoporosis; hormonal therapy as indicated
Sacral insufficiency fractures — Conservative management with rest, analgesics, and gradual mobilization. Most heal within 6–12 weeks.
Vertebral augmentation (vertebroplasty/kyphoplasty) — Considered for refractory vertebral body fracture pain after 4–6 weeks of conservative treatment
Sacroplasty — CT-guided injection of bone cement into the sacral ala for refractory sacral insufficiency fracture pain (performed at specialized centers)

Key Points¶

Insufficiency fractures result from normal forces on weakened bone (osteoporosis, radiation, steroids)
Sacral insufficiency fractures are a common but underdiagnosed cause of low back/buttock pain in the elderly
The "Honda sign" on bone scan and bilateral sacral alar edema on MRI STIR are characteristic
MRI with STIR is the most sensitive modality for both sacral and vertebral insufficiency fractures
Always evaluate for underlying causes (osteoporosis, malignancy, metabolic disease)
Treatment is primarily conservative with management of the underlying bone disease

References¶

Lyders EM, Whitlow CT, Baker MD, Morris PP. Imaging and treatment of sacral insufficiency fractures. AJNR Am J Neuroradiol. 2010;31(2):201-210. doi:10.3174/ajnr.A1666. PMC7964142
Fujii M, Abe K, Hayashi K, et al. Honda sign and variants in patients suspected of having a sacral insufficiency fracture. Clin Nucl Med. 2005;30(3):165-169. PubMed 15722819
Blake SP, Connors AM. Sacral insufficiency fracture. Br J Radiol. 2004;77(922):891-896. doi:10.1259/bjr/81974373. PubMed 15483007
Grangier C, Garcia J, Howarth NR, May M, Rossier P. Role of MRI in the diagnosis of insufficiency fractures of the sacrum and acetabular roof. Skeletal Radiol. 1997;26(9):517-524. doi:10.1007/s002560050278. PubMed 9342810
Oh D, Huh SJ. Insufficiency fracture after radiation therapy. Radiat Oncol J. 2014;32(4):213-220. doi:10.3857/roj.2014.32.4.213. PMC4282995
Uezono H, Tsujino K, Moriki K, et al. Pelvic insufficiency fracture after definitive radiotherapy for uterine cervical cancer: retrospective analysis of risk factors. J Radiat Res. 2013;54(6):1102-1109. PMC3823778