Sacral insufficiency fracture is a fracture in weakened bone (osteoporosis, post-pelvic radiation therapy, prolonged steroid use, Paget disease) under normal physiological stress. Most common in postmenopausal women >65 years, with prevalence of approximately 1-5% in the osteoporotic population. Frequently missed — most patients receive diagnoses of lumbar degenerative disease or sacroiliac joint pathology. STIR hyperintense bone marrow edema in the sacral ala and body on MRI forms the pathognomonic H-shape (Honda sign). CT shows thin fracture lines but sensitivity is lower than MRI. The Honda sign (H-pattern increased uptake) on bone scintigraphy is the classic finding. Pubic rami and other pelvic insufficiency fractures frequently accompany. Treatment is generally conservative (pain management, bed rest, osteoporosis treatment). Including the sacrum in lumbar MRI is critically important to avoid delayed diagnosis.
Age Range
55-90
Peak Age
72
Gender
Female predominant
Prevalence
Uncommon
Insufficiency fracture occurs in pathologically weakened bone under normal physiological stress — unlike stress fracture, the bone is abnormal, not the stress. In osteoporosis, trabecular bone density decreases and cortical bone thins — in this situation, body weight and daily activities apply sufficient mechanical load to the sacrum. The sacrum is the critical point where body weight is transmitted from the axial skeleton to the pelvic ring — the sacral ala carry most of this load. Fractures typically begin medial to the sacral foramina, in the weakest region of the sacral ala. The characteristic H-shape (Honda sign) forms when bilateral sacral ala fractures are joined by a transverse fracture through the sacral body. Bone marrow edema on MRI reflects the water content from micro-hemorrhage, inflammatory response, and reactive edema at the fracture site — producing high signal on STIR because free water appears bright after fat suppression. On T1, replacement of normal fatty bone marrow by edematous tissue appears as hypointensity. On CT, fracture lines are seen as disruptions in cortical bone continuity, but the low density of osteoporotic bone reduces the contrast between fracture line and normal bone — therefore CT sensitivity is lower than MRI. In post-pelvic radiation fractures, radiation damage causes osteoblast and osteocyte apoptosis, bone repair capacity decreases, and fractures develop under normal mechanical loads.
The pathognomonic finding of sacral insufficiency fracture: bilateral vertical hyperintense bone marrow edema in the sacral ala and transverse hyperintense band in the sacral body on coronal STIR MRI form the letter H. This finding is called the 'Honda sign' (named for its resemblance to the Honda Motor company logo from Japan where it was first described). It can also be seen as H-shaped increased uptake on bone scintigraphy. This sign confirms the diagnosis of sacral insufficiency fracture and distinguishes from differentials such as sacral metastasis and sacroiliitis.
Bilateral vertical hyperintense bone marrow edema in sacral ala + transverse hyperintense band in sacral body on MRI STIR/T2 fat-sat = H-shape (Honda sign). The two vertical components represent sacral ala fractures, the transverse component represents body fracture. Sometimes only unilateral (single wing) or without transverse component ('||' pattern) may be seen. Coronal STIR is the best evaluation plane.
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Bilateral symmetric bone marrow edema in the sacral ala and transverse edema band in the sacral body on coronal STIR MRI is identified, forming the Honda sign (H-shape) — consistent with sacral insufficiency fracture.
Thin vertical fracture lines (linear sclerosis or lucency) in the sacral ala and transverse fracture line in the sacral body. Fracture lines may be difficult to see in osteoporotic bone due to thinned trabecular structure. Axial and coronal reformatted images are required. Accompanying pubic rami fractures suggest pelvic insufficiency fracture complex.
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Bilateral vertical fracture lines in the sacral ala and a transverse fracture line in the sacral body are identified on CT, consistent with sacral insufficiency fracture; osteoporotic bone structure accompanies.
H-shaped (Honda sign) increased radiopharmaceutical uptake in the sacrum on bone scintigraphy (Tc-99m MDP). Bilateral sacral ala uptake forms vertical lines, sacral body uptake forms the transverse line. High sensitivity (96%) but low specificity — metastasis, infection, and Paget disease can also show increased uptake.
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H-shaped increased uptake in the sacrum (Honda sign) on bone scintigraphy is identified, consistent with sacral insufficiency fracture; MRI correlation is recommended for definitive diagnosis.
Hypointense signal in sacral ala and body on T1 — reflects replacement of normal fatty bone marrow by edematous tissue. H-shape may also be seen on T1 but may not be as prominent as STIR. T1 hypointensity + STIR hyperintensity combination is the bone marrow edema pattern and is important for distinguishing from malignant infiltration.
Report Sentence
Bilateral hypointense signal changes in the sacral ala on T1 are identified, demonstrating bone marrow edema pattern with accompanying STIR hyperintensity, consistent with sacral insufficiency fracture.
Associated pelvic insufficiency fractures: pubic rami fractures (superior and/or inferior), iliac wing fractures, acetabular fractures. Together with sacral insufficiency fracture, they form the 'insufficiency fracture complex'. Fracture at multiple points of the pelvic ring suggests pelvic instability.
Report Sentence
In addition to sacral insufficiency fracture, bilateral/unilateral pubic rami fractures are identified, consistent with pelvic insufficiency fracture complex.
Criteria
Fracture developing on the basis of postmenopausal or age-related osteoporosis. T-score ≤-2.5.
Distinct Features
Most common type. Women >65 years. Bilateral H-shape classic. Osteoporosis treatment (bisphosphonates, calcium, vitamin D) critical for secondary prevention.
Criteria
Fracture developing after pelvic radiation therapy (cervix, rectum, prostate cancer treatment). 6 months to 3 years post-RT.
Distinct Features
Distribution consistent with radiation portal. Diffuse increased uptake in radiation field on scintigraphy may mask fracture. Radiation bone marrow changes (T1 hyperintense fatty conversion) seen as background finding on MRI.
Criteria
Fracture developing on the basis of secondary osteoporosis from prolonged (>3 months) systemic corticosteroid use.
Distinct Features
Can occur at any age (unlike primary osteoporosis). Vertebral compression fractures may accompany. Steroid dose reduction and osteoporosis treatment needed.
Distinguishing Feature
Metastasis has focal asymmetric mass + soft tissue component, insufficiency fracture has bilateral symmetric linear edema (H-shape) + no soft tissue mass
Distinguishing Feature
AS has edema at SI joint surface (sacroiliitis), insufficiency fracture has edema in sacral ala (medial to foramina); AS young male, insufficiency fracture elderly female
Distinguishing Feature
Spondylolysis has pars interarticularis defect (lumbar), sacral insufficiency fracture has sacral ala fracture; different location, age, and mechanism
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
3-monthSacral insufficiency fracture usually heals in 6-12 weeks with conservative treatment (pain management, brief bed rest, gradual mobilization). Osteoporosis treatment (bisphosphonates, denosumab, calcium, vitamin D) is critical for secondary prevention — DEXA scan is recommended. Delayed diagnosis is common (average 4-6 weeks) — including the sacrum in the imaging field when ordering lumbar MRI is the most important practical measure. In post-pelvic radiation therapy patients presenting with pelvic pain, insufficiency fracture must be considered. Prognosis is excellent for stable fractures; unstable pelvic ring fractures rarely require surgical stabilization.
Sacral insufficiency fracture usually heals with conservative treatment (pain management, bed rest, osteoporosis treatment). Delayed diagnosis is common — including the sacrum in lumbar MRI is important. Osteoporosis treatment (bisphosphonates, calcium, vitamin D) should be initiated for secondary prevention. Should be considered in post-pelvic radiation therapy patients.