Stress & Insufficiency Fractures⁹⁹ᵐTc-MDP/HDP

Quick Answer

The bone scan is very sensitive and early for stress-related bone injury — often positive days to weeks before radiographs. A fatigue fracture is normal bone under abnormal load (athletes, military recruits); an insufficiency fracture is normal load on abnormal bone (osteoporosis, radiation, steroids). On the three-phase scan, an acute stress fracture is focal and hot on all three phases with a fusiform/focal cortical delayed pattern, versus the longitudinal, mild, cortical uptake of shin splints (tibial stress syndrome). SPECT/CT localizes spondylolysis (pars) and characterizes the classic sacral insufficiency "Honda/H sign."

Fatigue vs insufficiency

Same imaging, two mechanisms: a fatigue fracture is abnormal stress on normal bone (running, marching), and an insufficiency fracture is normal stress on weakened bone (osteoporosis, prior radiation, chronic steroids, renal disease). The bone scan is positive early — often before radiographs — making it valuable when plain films are negative but clinical suspicion is high.

Patterns by site

Recognize the site-specific patterns:

Why SPECT/CT matters here

SPECT/CT converts a nonspecific hot spot into a diagnosis: it separates active spondylolysis (treatable) from an old defect, distinguishes facet arthropathy from a pars stress reaction, and confirms the sacral insufficiency pattern (avoiding a false call of metastasis). It also grades the stress-injury continuum from stress reaction to frank fracture.

High-Yield Pearls

• The bone scan is positive early — before radiographs — in stress injury.
• Shin splints = longitudinal cortical uptake on the delayed phase; an acute stress fracture is focal and hot on all three phases.
• The Honda/H sign = bilateral sacral ala uptake = sacral insufficiency fracture (not metastasis).
• SPECT/CT dates and localizes spondylolysis (pars) — active vs old.

Common Pitfalls

• Reading a sacral insufficiency fracture (Honda sign) as metastatic disease.
• Confusing shin splints (longitudinal, delayed only) with an acute stress fracture (focal, three phases).
• Relying on negative radiographs to exclude stress injury when the bone scan/MRI would be positive.

Related Pages

• Protocol: Bone scintigraphy (three-phase technique); imaging comparison: Skeletal metastases.

Differential Diagnosis

• Metastasis / malignancy — typically focal, randomly distributed, marrow-based foci, often multiple, without a loading-site pattern; a stress/insufficiency fracture is linear/fusiform and cortical at a characteristic mechanical site, and the sacral Honda/H pattern favors insufficiency over metastasis.
• Osteoid osteoma — intense focal uptake with a "double-density" sign (hotter central nidus within a larger reactive area) and a lucent nidus with surrounding sclerosis on CT; night pain relieved by NSAIDs.
• Osteomyelitis — focal uptake on all three phases but with soft-tissue hyperemia and a clinical infection picture; SPECT/CT and history separate it from cortical stress injury.
• Degenerative change / enthesopathy and bone island (enostosis) — usually less avid and at joint/entheseal sites; correlate with CT.

Reporting Checklist

• State the site and pattern (focal/fusiform cortical vs longitudinal) and which phases are positive (three-phase vs delayed-only).
• Classify fatigue vs insufficiency from the clinical context and note risk factors (osteoporosis, prior radiation, chronic steroids, renal disease).
• For the sacrum/pelvis, describe the Honda/H pattern and explicitly state it favors insufficiency fracture over metastasis.
• Recommend or perform SPECT/CT for spinal (pars) and pelvic lesions to localize, date (active vs old), and exclude a malignant mimic.
• Note that a negative radiograph does not exclude stress injury; correlate with MRI where uptake is equivocal.

Self-Check

Key References

• SNMMI bone scintigraphy guideline; reviews of three-phase bone scan and SPECT/CT in stress injury and spondylolysis.
• Literature on sacral insufficiency fracture scintigraphic patterns (Honda sign).