Fracture, Sacral

By admin On Sep 29, 2023

Ovid: 5-Minute Sports Medicine Consult, The

Fracture, Sacral

Michele LaBotz

Basics

Sacral injuries are rare, but most authors believe that sacral fractures are generally under-recognized.
A high degree of suspicion is required to make the diagnosis:
- Standard radiographs of the lumbar spine and pelvis are often normal.
- Advanced imaging is often required to appreciate sacral injury.

Description

Traumatic fractures of the sacrum are most commonly described using the Denis system of fracture orientation:
- Zone I:
  - Fracture line usually vertically through the sacral ala
  - Entirely lateral to foramina
  - Typically, strength of sacroiliac (SI) ligaments spares SI joint from injury, but fractures that enter SI joint at greater risk for instability
  - Neural elements typically spared; 6% with neurologic involvement
- Zone 2:
  - Fracture line involving the neural foramen, but sparing the central spinal canal
  - 28% with neurologic injury
- Zone 3:
  - Fracture line involving the spinal canal; typically includes transverse fractures
  - 58% with neurologic injury
Atraumatic injuries result from a mismatch between bone stress and bone strength:
- Nomenclature is typically broken down into the following categories:
  - Stress fractures in athletes; typically unilateral fracture of sacral ala
  - Insufficiency fractures in elderly or infirm; often bilateral fractures of sacral alae; may also have horizontal component

Epidemiology

Sacral fractures need to be considered in several clinical scenarios:

Multitrauma patients with other pelvic or thoracolumbar injury:
- Sacral fractures rarely occur as isolated injury (<5%)
Osteoporotic patients with low back or gluteal pain:
- Atraumatic or trivial injury
Athletes with activity-related pain of low back/SI region:
- Usually in running based sports:
  - Often after increases in training intensity
- May produce thigh pain as well

Risk Factors

Insufficiency fractures are most common in elderly osteoporotic females:
- May occur in others at risk for poor bone density, including the following:
  - Chronic corticosteroid use
  - History of pelvic irradiation
Stress fractures occur most commonly in running athletes:
- As with other stress fractures, risk probably increases with the following:
  - Training errors (inadequate recovery, increasing training, etc.)
  - Biomechanical factors (leg length discrepancy, poor core and pelvic stabilization)
  - Increased impact forces (footwear, training surface)
  - Nutritional/hormonal impacts on bone density (disordered eating/female athlete triad, inadequate calcium/vitamin D)

Etiology

Sacral fractures may occur by the following mechanisms:

Post-traumatic injuries:
- Producing large forces and fracture across healthy bone:
  - Typically motor vehicle accidents or falls from a height
Atraumatic injuries:
- Normal stresses (or trivial injury) producing fractures across relatively weakened bone:
  - Insufficiency fractures in the elderly/ill
  - Fractures often bilateral
- Increased stress or overuse, producing fracture across relatively normal bone:
  - Stress fractures in the younger, athletic population
  - Fractures often unilateral

Commonly Associated Conditions

Acute sacral fractures may be seen in conjunction with:

Other bony injury:
- Other pelvic ring disruptions
- Other spinal fractures:
  - May be noncontiguous
- Fracture-dislocations of lower facet joints or disruption of lumbosacral junction
Neurologic injury:
- Should be described according to the Gibbons grading system:
  - Grade 1: No neurologic deficit
  - Grade 2: Paresthesias/sensory changes only
  - Grade 3: Motor deficit, but gastrointestinal (GI)/genitourinary (GU) function normal
  - Grade 4: Loss of GI/GU function
Injury to other pelvic contents:
- Rectal perforation most common

Diagnosis

Pre Hospital

Traumatic sacral fractures typically occur in the multitrauma patient.
Initial assessment and treatment should proceed as per Advanced Trauma Life Support for patients with suspected spine injury:
- ABCs/resuscitation
- Spine precautions/backboard
- Transport

History

Injury to sacrum is suggested by pain in lower back, buttocks, perirectal region, and posterior thigh
Important to inquire about possible nerve root involvement:
- Incontinence of bowel or bladder, sexual dysfunction
- Sciatica
- Paresthesias, especially of saddle region
Patients without history of trauma should be asked about:
- Change in activity or footwear, especially in running-based sports
- Risk factors for poor bone density:
  - Osteopenia/osteoporosis in patient or family members
  - Past or present disordered eating pattern
  - Oligo- or amenorrhea in females

Physical Exam

Trauma patient:
- Inspect for ecchymosis/bruising over sacral prominence
- Palpate entire spinal column and bony pelvis in addition to the sacrum.
- Neurologic testing of L5–S5 nerve root function should be completely assessed initially then periodically re-evaluated:
  - Pinprick sensation, rectal sphincter contraction and tone, as well as cremasteric, bulbocavernosus, perianal wink reflexes
  - L5 injuries most common with Zone 2 injuries
  - Sacral roots have bilateral input, and unilateral injuries to S2–5 are difficult to detect.
- Digital rectal and vaginal evaluation to exclude open fractures
Atraumatic patient with possible insufficiency or stress fracture:
- No pathognomonic findings
- Typically with tenderness over sacrum, paraspinal, or over region of SI joint
- FABER test (with hip in flexion, abduction, external rotation) often positive
- Distal neurovascular assessment typically normal
- Gait may be antalgic and may have pain with a hop test

Diagnostic Tests & Interpretation

Lab

Trauma patients should have stool assessed for occult blood.
Otherwise, assessment should proceed as directed by other possible injury.

Imaging

Traumatic injury:
- Although radiographs typically only reveal about 30% of sacral fractures, they may be useful for initial assessment of suspected sacral injury:
  - AP views of the pelvis are standard in multitrauma patients
  - Visualization of suspected sacral injuries may be enhanced with the addition of pelvic inlet view: 35–40 degree caudal tilt of radiograph tube; pelvic outlet view: 45-degree cranial tilt of radiograph tube; lateral view of sacrum
  - Look for transverse L5 fractures, which can be seen in up to half of pelvic and sacral fractures.
- CT scanning is now standard for definitive assessment of suspected acute sacral fracture:
  - Routine CT scans often not satisfactory
  - Close consultation with radiologist on gantry alignment recommended
  - Thin section (1.0–1.5 mm cuts) with coronal and sagittal reconstructions; relatively high radiation exposure: 10–20 mSV
- MRI may help delineate neural compression or injury:
  - Multiplanar nature may also better assess fracture alignment

P.249

Atraumatic injury:
- Since typical presentation is of lumbar or gluteal pain, initial lumbar spine series as well as anteroposterior views of the pelvis are often obtained:
  - Usually unremarkable
- MRI of sacrum appropriate for diagnosis:
  - Some authors report not as sensitive as bone scan
  - Most bony stress injuries will have high signal on T2-weighted images, low signal on T1-weighted images.
  - Fracture line may or may not be present.
- Bone scan most sensitive, but not specific for bony stress injury:
  - Stress fractures in athletes; typically with unilateral uptake sacral ala
  - Insufficiency fractures; often with multiple sites of injury; classic “H” sign seen in about 40% of patients; bilateral vertical fractures with horizontal component
  - Uptake can be obscured by residua in bladder; outlet views in addition to standard anterior and posterior projections

Differential Diagnosis

Differential diagnosis for acute fractures:
- Contusion
- Other pelvic or lumbar fractures
- Nerve root injuries
Differential diagnosis for atraumatic/stress fractures:
- Lumbar disc disease
- Mechanical low back pain
- Sacroiliac dysfunction
- Spondylolysis

Treatment

Acute fracture:
- See below for surgical indications
- Stable injuries without neurologic involvement treated with initial bed rest and gradual ambulation and activity advancement as tolerated:
  - Fractures through S3 and distally often require protection with sitting until pain-free
Stress fracture: Average +/-6 wks for return to sport (but some may take up to 3 mos)
- Protected weight-bearing if limp or pain with ambulation:
  - Advance weight-bearing as tolerated
- Discontinue painful activity/relative rest
- Maintain cardiovascular conditioning with pain-free activity:
  - May need to begin with non-weight-bearing activity (typically swimming or cycling)
- Begin progressive rehabilitation typically after 3–5-day pain-free interval:
  - Core/pelvic stabilization; address underlying biomechanical deficiencies
  - Cardiovascular cross-training progression through following sequence when activity is pain-free: Non-weight-bearing (ie, pool running, bicycling), weight-bearing/nonimpact (ie, elliptical-type trainer), impact (ie, running), sports-specific functional progression
Insufficiency fractures in elderly may have prolonged symptoms (up to 9 mos):
- Initial treatment is usually nonoperative, even for patients with neurologic deficit:
  - Many authors recommend initial period bed rest followed by progressive ambulation
  - Neurologic symptoms appear to improve as pain resolves.
- Consider surgery if severe pain after 3-mon trial conservative treatment

Medication

Analgesics should be titrated for symptom relief:
- Scheduled doses for first several days of diagnosis may allow for pain-free rest:
  - Over-the counter analgesics often sufficient for stress fractures: Acetaminophen, up to 1,000 mg q4h PRN; pediatric dosage 10–15 mg/kg up to q4h Nonsteroidals often beneficial. Theoretically may impair bony healing, but no consensus on effect on clinical outcomes. Naproxen 500 mg q12h; pediatric dosage 10–20 mg/kg/day divided b.i.d.
- Patients with severe pain may need stronger medications for first several days:
  - Hydrocodone/acetaminophen 5/500 1–2 PO. q4–6h PRN; pediatric suspension 7.5/500/15 mL; patient weight 32–45 kg: 10 mL q4–6h PRN
  - Tramadol 50 mg 1–2 tabs q4–6h PRN; maximum dose 400 mg/day; caution in elderly and with renal or hepatic impairment
Analgesics should not be used specifically to allow for progression of activity or sport participation

Surgery/Other Procedures

Surgical consideration for traumatic sacral fractures:
- Unstable injuries
- Severe disruption of sagittal or coronal alignment:
  - In AP plane displacement, >1 cm generally recognized as unstable
- Neurologic impairment
- Injuries with persistent pain after about 6 mos
Insufficiency fractures considered for surgery if with persistent, severe pain after 3 mos conservative treatment

In-Patient Considerations

Stress fractures and insufficiency fractures are generally managed in outpatient setting.
Acute traumatic sacral fractures often require hospitalization for additional injury:
- Isolated and stable Zone 1 or 2 fractures with no neurologic deficit and adequate pain control may be considered for outpatient treatment.

Ongoing Care

Sacral stress or insufficiency fractures may be a bellwether for underlying metabolic bone disease:

Bone density testing or other laboratory evaluation should be considered.

Diet

Patients with insufficiency or stress fractures should be counseled on appropriate intake of calcium and vitamin D.

Patient Education

Education should focus on biomechanical issues and training errors predisposing to injury:

Importance of maintaining adequate strength and flexibility of core and pelvic musculature
Advance training volume by ∼10%/wk to minimize risk of additional overuse injury
Especially in the running athlete, the importance of appropriate footwear selection:
- Effective lifespan of most running shoes is 300–400 miles

Prognosis

Healthy athletes with sacral stress injury:
- Usually able to return to normal activity 4–6 wks
- Usually able to return to sport 6–10 wks
Elderly patients with insufficiency fractures may have pain for many months.
Fractures requiring surgery often with instrumentation:
- Up to 1/3 may have hardware failure.

Complications

Deformity or bony callus formation after acute injury may lead to nerve root entrapment.
Prolonged pain common in elderly with insufficiency fractures.

Additional Reading

Micheli LJ, Curtis C. Stress fractures in the spine and sacrum. Clin Sports Med. 2006;25:75–88.

Shah MK, Stewart GW. Sacral stress fractures: an unusual cause of low back pain in an athlete. Spine. 2002;27:E104–E108.

White JH, Hague C, Nicolaou S, et al. Imaging of sacral fractures. Clinical Radiology. 2003;58: 914–921.

Kuklo TR, Potter BK, Ludwig SC, et al. Radiographic measurement techniques for sacral fractures consensus statement of the Spine Trauma Study Group. Spine. 2006;31:1047–1055.

Levine AM. Fractures of the sacrum in browner: skeletal trauma, 4th ed. Philadelphia: Saunders, 2008.

Shah MK, Stewart GW. Sacral stress fractures: an unusual cause of low back pain in an athlete. Spine. 2002;27:E104–E108.