Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

Featured on Channel NewsAsia

Sacral Insufficiency Fracture

Basics
Description
  • Sacral Insufficiency fractures occur in the sacral ala between the SI joints and the neural foramina (Denis Zone 1).
    • The fracture pattern adopts a characteristic H-shape, which is pathonemonic of the condition.
    • It is postulated that the vertical limbs of the H occur 1st, followed by the transverse fracture line.
    • In ~50% of cases, the fracture results from low-energy trauma such as a fall.
  • Sacral insufficiency fractures often are associated with other insufficiency fractures around the pelvic girdle, most commonly the pubic rami.
General Prevention
Maintenance of adequate bone mineral density in patients with osteoporosis, including bone density monitoring and treatment with calcium, vitamin D, and bisphosphonates
 
Epidemiology
  • >90% occur in postmenopausal females
  • Predominantly Caucasian females
Incidence
  • Currently, the true incidence is unknown, but based on the fact that plain radiographs do not diagnose the injury, they may be grossly underreported.
  • It is estimated that 1-2% of patients attending a rheumatology clinic with lumbar pain have an insufficiency fracture of the pelvic girdle.
Risk Factors
  • Osteoporosis
  • Inflammatory arthritis
  • Primary bone or metastatic neoplasms
  • Radiotherapy
  • Metabolic bone disease
  • Corticosteroids
  • Total hip replacement
Pathophysiology
  • The mechanism of injury has yet to be defined, but theoretically:
    • During ambulation, load is transmitted from the spine through the sacrum around the pelvic rim to the lower limbs.
    • In people with osteoporosis, the tilting and rotation of the pelvis during ambulation or sudden load transmission during a fall creates shear forces that generate microfractures vertically in the sacral ala.
    • These fractures may be unilateral initially before progressing bilaterally.
    • Continued tilting and rotation of the pelvis around 2 cross-axes lead to microfracture transversely between the 2 vertical fracture lines.
  • This theory explains the characteristic H or butterfly appearance on bone scintigraphy and why, in some sacral insufficiency fractures, only 1 or 2 vertical fractures are apparent, depending on how far the fracture has propagated before the diagnosis is made.
Etiology
  • Sometimes no antecedent trauma is apparent.
  • Low-energy fall in up to 50%
Associated Conditions
  • Other insufficiency fractures around the pelvic girdle
  • Vertebral compression fractures
  • Osteoporosis
Diagnosis
Signs and Symptoms
  • No clear set of symptoms that pinpoints the diagnosis
  • Suspicion of a sacral insufficiency fracture should be raised in the presence of mechanical low back and buttock pain.
  • Pain is exacerbated by sitting or mobilizing.
History
  • Low back and buttock pain of gradual onset that is relieved by lying down.
  • Sometimes a fall is recalled on questioning.
  • Diagnosis of cancer
  • Recent radiotherapy
  • Previous or concurrent insufficiency fracture of the pelvic girdle
  • Corticosteroids
Physical Exam
  • Pain on palpation of sacrum
  • Pain with weightbearing
Tests
Lab
Alkaline phosphatase may be elevated.
Imaging
  • Plain radiographs are unhelpful (rarely show fracture).
  • Bone scintigraphy is the test of choice (shows characteristic H-shape).
  • CT can outline the fracture accurately.
  • MRI signs are sensitive but not specific:
    • Band of low signal on T1-weighted images
    • High-signal associated with edema on T2-weighted images
Diagnostic Procedures/Surgery
DEXA scan to determine bone density
Differential Diagnosis
  • Malignancy
  • Infection
Treatment
Initial Stabilization
  • Pain relief
  • Bed rest
General Measures
Activity
  • Sacral insufficiency fractures are stable.
  • Once pain is controlled, the patient should be mobilized to avoid complications associated with prolonged recumbency.
  • Early mobilization reduces additional bone demineralization.
Nursing
  • Patients at rest should be monitored carefully for decubitus ulcers.
  • Patients on narcotics should be given stool softeners.
Special Therapy
Physical Therapy
Therapy may help in strengthening after the fracture is healed.
Medication
First Line
  • Acetaminophen
  • Oral narcotic analgesics
Second Line
  • Calcium
  • Vitamin D
  • Calcitonin
  • Diphosphonates
Surgery
  • In cases of prolonged and persistent pain resistant to analgesics, sacroplasty may be considered.
    • Percutaneous injection of small aliquots of bone cement into the fracture site to prevent micromotion at the fracture
    • Performed under regional or general anesthetic using CT guidance
    • The use of bone cement in this manner is not FDA approved.
  • Operative internal fixation can improve pain in patients with established nonunion of the sacrum.
Follow-up
Patients should be monitored with radiographs of the pelvis at 6-8-week intervals until pain free.
Disposition
Issues for Referral
  • Awareness of these insufficiency fractures is key.
  • Patients whose fractures do not heal should be referred to an orthopaedist.
  • Patients with severe osteoporosis may need referral to an osteoporosis specialist for metabolic workup.
Prognosis
Most reported cases treated nonoperatively heal in 3-4 months.
Complications
  • Nonoperative treatment:
    • Delayed union
    • Recurrent Insufficiency fracture
  • Operative treatment:
    • Damage to iliac vessels
    • Damage to lumbosacral nerve roots
    • Chronic pain
Miscellaneous
Codes
ICD9-CM
  • 805.6 Fracture sacrum, closed
  • 808.2 Fracture pubis, closed
  • 808.43 Multiple pelvic fractures, closed
Patient Teaching
Activity
  • Activity should be restricted to a level that does not cause pain.
  • Assistive devices, such as a walker or a cane, should be used during healing.
Prevention
  • Maintain mobility.
  • Adequate daily calcium in diet
  • Osteoporosis prevention and treatment
FAQ
Q: How are sacral insufficiency fractures treated?
A: With activity modification, ambulatory aids, and oral pain medicines. Osteoporosis should be treated.

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