Why are subtrochanteric fractures less common than intertrochanteric fractures in the elderly?

Why Subtrochanteric Fractures Are Less Common Than Intertrochanteric Fractures in the Elderly

Subtrochanteric fractures are less common than intertrochanteric fractures in the elderly primarily due to differences in bone vascularity, biomechanical forces, and underlying bone quality in these anatomical regions.

Anatomical and Biomechanical Factors

• Fracture Distribution: Approximately 50% of hip fractures are intracapsular (femoral neck), while the other 50% are extracapsular (intertrochanteric and subtrochanteric), with subtrochanteric fractures being the least common 1

• Blood Supply Differences:

  • Intertrochanteric region: Has rich blood supply from cancellous bone, which can lead to significant blood loss (>1 liter) when fractured 1
  • Subtrochanteric region: Has relatively less vascularity compared to the intertrochanteric region

• Biomechanical Forces:

  • The intertrochanteric region experiences higher compressive and shear forces during falls in the elderly
  • The subtrochanteric region is subjected to different biomechanical stresses that make it less susceptible to typical fragility fractures

Patient Characteristics and Risk Factors

• Age and Health Status: Patients with intertrochanteric fractures tend to be older and in poorer health compared to those with femoral neck fractures 2, 3

• Bone Quality:

  • Intertrochanteric fractures are more associated with poor health status (OR = 0.74; 95% CI = 0.55-1.00) 3
  • Femoral neck fractures are more strongly predicted by bone mineral density and functional ability 3

• Epidemiological Trends: While typical hip fractures (femoral neck and intertrochanteric) have decreased over time, subtrochanteric fractures have shown different patterns, with some studies showing a slight increase in women (20.4% increase from 1999 to 2007) 4

Clinical Implications

• Blood Loss: Intertrochanteric fractures result in greater blood loss than femoral neck fractures, with subtrochanteric fractures often requiring blood transfusions (49.8% compared to 18.5% for femoral neck fractures) 5

• Pain Levels: Extracapsular fractures (intertrochanteric and subtrochanteric) are generally more painful than intracapsular fractures due to greater periosteal disruption 1

• Treatment Approaches:

  • Intertrochanteric fractures: Typically treated with sliding hip screws for stable fractures or cephalomedullary nails for unstable fractures 1
  • Subtrochanteric fractures: Strong evidence supports the use of cephalomedullary devices 1, 6

Mortality and Complications

• Mortality: Risk-adjusted 30-day mortality is not significantly different between subtrochanteric (5.8%) and intertrochanteric (7.3%) fractures compared to femoral neck fractures (6.6%) 5

• Complications: While overall medical adverse events are similar across fracture types, subtrochanteric fractures have higher rates of blood transfusion requirements 5

Conclusion

The lower incidence of subtrochanteric fractures in the elderly compared to intertrochanteric fractures can be attributed to differences in bone vascularity, biomechanical forces during falls, and underlying patient characteristics. Understanding these differences is important for proper fracture management and patient counseling regarding expected outcomes.