What is the probable cause of a shaft humerus fracture in a newborn?

Probable Cause of Humeral Shaft Fracture in Newborns

Birth trauma during delivery is the most probable cause of humeral shaft fractures in newborns, occurring most commonly with difficult extractions, breech presentations, macrosomia, and operative deliveries including both vaginal and cesarean deliveries. 1, 2, 3, 4

Primary Etiologies in Newborns

Birth-Related Trauma (Most Common)

• Humeral fractures are the second most common long bone birth injury after clavicle fractures, accounting for approximately 20% of all birth-related bone injuries 4
• Risk factors include:
  • Breech presentation (most strongly associated) 1, 3, 5
  • Macrosomia (large birth weight) 3
  • Obstructed labor 4
  • Operative deliveries (forceps, vacuum extraction) 4
  • Difficult extractions during cesarean section with energetic traction or improper uterine incisions 2, 5
• Lack of antenatal care increases risk 4

Important Clinical Context

• Cesarean section does NOT eliminate the risk of humeral fractures; forceful maneuvers and traction during cesarean delivery can cause these fractures, though they may go unnoticed by the obstetrician 2, 5
• Birth-related humeral fractures typically present on the first day of life with pseudoparalysis (infant not moving the affected limb) 1, 2

Critical Differential Considerations

Child Abuse (Must Be Evaluated)

While birth trauma is most common in true newborns, child abuse must be considered, particularly in non-ambulatory infants younger than 3 years old 6, 3:

• Long bone shaft fractures have LOW specificity for abuse but can still be inflicted 6
• Humeral fractures are MORE LIKELY to be abusive in non-walking children compared to ambulatory children 6
• Approximately one-quarter of fractures in children younger than 1 year are caused by abuse 6

Red flags for abuse include 6:

• No history of injury or implausible mechanism
• Inconsistent or changing histories from caregivers
• Multiple fractures or fractures of different ages
• Delay in seeking medical care
• Other injuries suspicious for abuse (bruising, internal injuries, CNS trauma)

Metabolic Bone Disease (Less Common in Isolated Cases)

Osteopenia of prematurity 6, 7:

• Affects infants born <28 weeks gestation or <1500g birth weight 6
• Risk factors: prolonged total parenteral nutrition (≥4 weeks), bronchopulmonary dysplasia, prolonged diuretics or steroids 6
• Fractures typically occur between 6-12 weeks of life, not immediately at birth 6
• Although osteopenia increases fracture vulnerability, preterm infants are also at increased risk of abuse 6

Osteogenesis imperfecta (OI) 6:

• Should be suspected with: family history of fractures, blue sclerae, poor dentition, short stature, triangular face, hearing impairment 6
• Multiple long bone fractures or rib fractures in infancy WITHOUT other clinical/radiographic evidence of OI is unusual 6
• Child abuse is more common than OI, and children with OI can also be abused 6

Vitamin D deficiency/rickets 6:

• Does NOT cause fractures in non-mobile newborns 6
• Fractures from rickets occur only in mobile infants (8-19 months) 6
• Metaphyseal fractures in rickets occur closer to diaphysis with florid rachitic changes, distinct from abuse-related classic metaphyseal lesions 6

Diagnostic Approach

Immediate evaluation should include 1, 2:

• Radiography AND ultrasonography (ultrasound is particularly useful for unossified epiphyses) 1
• Detailed birth history: presentation, delivery method, complications, birth weight 3, 4
• Examination for other injuries or signs of metabolic bone disease 6

If birth trauma is not clearly documented or history is concerning 6:

• Obtain skeletal survey to evaluate for other fractures
• Detailed social history and assessment for abuse risk factors
• Consider metabolic workup if clinical features suggest bone fragility disorder

Common Pitfalls to Avoid

• Do not assume cesarean section eliminates birth trauma risk—fractures can occur with difficult cesarean extractions 2, 5
• Do not dismiss abuse solely because there is a birth trauma history—verify documentation and ensure history is consistent 6
• Do not attribute isolated humeral shaft fractures to osteopenia or rickets without supporting clinical/laboratory evidence 6
• Do not confuse birth-related humeral fracture with brachial plexus injury (Erb's palsy)—examine for swelling, crepitus, and obtain imaging 2