Seat Belt Sign

Aka: Seat Belt Sign, Seat Belt Syndrome, Seatbelt Sign

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II. Precautions

  1. Seat Belts restraints are critical protection against ejection and serious Head Injury
    1. Benefits of Seat Belts far outweigh the risks of Seat Belt Syndrome
  2. In children, Car Seats reduce the risk of MVA-related injury by 71 to 82%
    1. Booster Seats, when properly used decrease serious injury rates by 45%
    2. However, up to 25% of children age 4 to 7 years are transitioned to adult Seat Belt too soon

III. Pathophysiology

  1. Seat Belt Syndrome
    1. Lap belt acts as a fulcrum with flexion and other injuries (spine, viscus, vasculature) in this plane

IV. Signs

  1. Abdominal abrasions and Contusions associated with Seat Belt lap restraint
  2. Neck Contusion associated with the Shoulder belt

V. Complications: Seat Belt Syndrome in Adults

  1. Aortic Injury
  2. Abdominal organ injury (Lap belt injury)
    1. See Blunt Abdominal Trauma
    2. Seat Belt Sign is associated with abdominal organ injury in 65% of cases
    3. Associated with mesentary bucket handle injury and Small Bowel injury
      1. Risk of bowel ischemia and delayed peritonitis
    4. Relative Risk of significant intra-Abdominal Injury: 8
    5. Obtain CT Abdomen in nearly all cases
      1. CT Findings in Seatbelt Sign with increased risk of hollow viscus injury (9% overall risk)
        1. Abdominal wall soft tissue Contusion
        2. Free fluid (even small free fluid in women, RR 40 for hollow viscus injury)
        3. Bowel wall thickening
        4. Mesenteric stranding
        5. Mesenteric Hematoma
        6. Bowel dilation
        7. Pneumatosis or pneumoperitoneum
        8. Delaplain (2022) JAMA Surgery 157(9):771-8 +PMID: 35830194 [PubMed]
      2. Negative CT Abdomen
        1. Consider observation for 12-24 hours (East U.S. Trauma Surgery Guidelines)
        2. Close interval follow-up may be acceptable (discuss with local Trauma surgery)
        3. Modern CT Abdomen has a high Negative Predictive Value for hollow viscus injury
          1. Sufficient for discharge with close interval follow-up
          2. Delaplain (2022) JAMA Surg 157(9): 771-8 +PMID: 35830194 [PubMed]
      3. Equivocal CT Abdomen (trace free fluid, bowel wall thickening or stranding)
        1. Observe for 12-24 hours with serial examinations
        2. Surgery for fever, peritoneal signs, clinically worsening
        3. May disposition home if pain resolved, tolerating fluids, stable Vital Signs
      4. Positive CT Abdomen
        1. Surgery (Laparotomy)
  3. Lumbar Fracture at L1 (Chance Fracture)
    1. See Chance Fracture
    2. Uncommon, but high risk, unstable Fracture associated with Seat Belt use without Shoulder restraint
    3. Surgery evaluation required to determine Fracture stability
  4. Blunt Neck Trauma
    1. See Blunt Neck Trauma
    2. See Cervical Spine Imaging in Acute Traumatic Injury
    3. Associated with Shoulder belt
    4. Presents with anterior neck Bruises
    5. May be associated with Laryngeal Fracture, tracheal Fracture, carotid injury

VI. Complications: Seat Belt Syndrome in Children

  1. See Pediatric Blunt Abdominal Trauma
  2. See Pediatric Blunt Abdominal Trauma Decision Rule
  3. Seat Belt Sign had intraabdominal injuries in 5.7% of children without Abdominal Pain, tenderness (2% required surgery)
    1. Mahajan (2015) Acad Emerg Med 22(9): 1034-41 [PubMed]
  4. Car Restraints significantly reduce the risk of injury and death, but must be used properly
    1. Car Seats should be used up to age 4 years old (rear facing until age 2 years)
    2. Booster Seats should be used from age 4-8 years old (until height >=57 inches)
      1. Premature use of the adult Shoulder-Lap belt risks neck extension and flexion injuries
  5. Lap belt is intended to rest over the pelvic brim (anterior superior iliac spine)
    1. Younger child Pelvis can not support the Lap belt restraint
    2. Restraint may ride high over the soft tissues of the Abdomen in children ("submarine effect")
      1. Results in greater transmission of MVA forces to the spine, vessels and organs
      2. Children also have less protection from their weak abdominal Muscles and less abdominal fat
  6. Blunt Abdominal Trauma from Seat Belt Syndrome associated injuries in children
    1. Precautions
      1. Up to 6% of asymptomatic children with Seat Belt Sign have intraabdominal injuries
      2. Lack of Seat Belt Sign does NOT exclude intraabdominal injury
        1. Closely observe and evaluate symptomatic children (e.g. Abdominal Pain, back pain)
        2. See Pediatric Blunt Abdominal Trauma
        3. See Pediatric Blunt Abdominal Trauma Decision Rule
    2. Red flag findings with higher risk of Seat Belt-related Trauma
      1. Abdominal Bruising from Lap belt (defining feature and highest risk)
      2. Abdominal or back tenderness
      3. GCS Score <15
      4. Hypotension
      5. External thoracic Trauma
      6. Lutz (2004) J Pediatr Surg 39(6): 972-5 [PubMed]
    3. Gastrointestinal Trauma (present in 11% of cases with Seat Belt Sign)
      1. See Pediatric Blunt Abdominal Trauma
      2. Bowel perforation
      3. Bowel wall Hematoma
      4. Mesenteric tear
      5. Mesenteric vessel devascularization
      6. Solid organ injury is less well correlated but may affect Spleen, liver, Kidney or Pancreas
    4. Lumbar Fracture or Chance Fracture (esp. L2-3)
      1. Most Chance Fractures have a good prognosis with appropriate management
      2. Associated permanent neurologic injury (10%) is far less common than in unrestrained children (42%)
      3. Associated with Abdominal Injury concurrently in 15% of cases
  7. Shoulder straps of 3-point restraints are intended to lie over the clavicle and Sternum (age >8 years)
    1. Children age 4 to 8 years require a Booster Seat for proper fitting of the Shoulder strap
    2. Young children (age <8 years) without a Booster Seat blunt neck injury (see below)
  8. Blunt Neck Trauma related to Shoulder belt
    1. See Blunt Neck Trauma
    2. Higher risk of neck injury if premature transition from Booster Seat to lap-Shoulder belt
    3. Children age <8 years have larger head to body ratios
      1. See Pediatric Cervical Spine Injury
      2. Upper Cervical Spine Injury represents 85% of restraint related injuries in this age group
      3. Ligamentous Injury is most common in age <8 years old
      4. Vertebral Fractures are more common in age >8 years old
    4. Cerebrovascular injuries are uncommon in properly restrained children age <12 years
      1. Neck Bruising from Shoulder strap is associated with vascular injury in adults
        1. In contrast, neck Bruising in children has less evidence based approach for vascular injury
        2. As in adults, CT angiography is recommended if vascular injury is suspected
          1. However, Shoulder-belt Bruising alone does not mandate CT angiography
      2. Findings in addition to neck Bruising with increased vascular injury risk (CT angiography indications)
        1. Depressed GCS score (esp. <8)
        2. Upper Cervical Spine Injury
        3. Focal neurologic deficit
        4. Carotid canal Fracture
        5. Petrous Temporal BoneFracture
        6. Non-contrast Head CT with hypodensity (Hematoma) in the region of the neck
      3. References
        1. Nickoles (2023) J Trauma Acute Care Surg 95(3): 334-40 [PubMed]
        2. Desai (2014) AJNR Am J Neuroradiol 35(9): 1836-40 [PubMed]

VII. Resources

  1. Trauma Professional's Blog
    1. http://regionstraumapro.com/post/663723636

VIII. References

  1. Enabore and Ruttan (2024) Crit Dec Emerg Med 38(4): 4-11
  2. McClung and Ruttan (2019) Crit Dec Emerg Med 33(3): 3-11
  3. Spangler and Inaba in Herbert (2016) EM:Rap 16(5): 6-7
  4. Lutz (2004) J Pediatr Surg 39(6): 972-5 [PubMed]
  5. Borgialli (2014) Acad Emerg Med 21(11): 1240-8 [PubMed]

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