Classification of Intertrochanteric Hip Fractures
The AO classification system is recommended for intertrochanteric hip fractures, with the new AO classification (2021) demonstrating superior inter-observer agreement compared to the original system, particularly when distinguishing stable from unstable fracture patterns. 1
Primary Classification Systems
The most clinically relevant approach uses the AO classification system, which categorizes intertrochanteric fractures as:
- 31-A1 fractures: Simple two-part fractures (stable patterns) 2
- 31-A2 fractures: Multifragmentary fractures with some stable variants 2
- 31-A3 fractures: Reverse obliquity and subtrochanteric extension patterns (unstable) 3
The new AO classification achieves moderate agreement (k = 0.425) when used as a dichotomous variable to distinguish stable versus unstable patterns, compared to only slight agreement (k = 0.158) with the original classification. 1
Alternative Classification Systems Referenced in Guidelines
While the AO system is most validated, other systems mentioned in clinical practice include:
- Evans classification: Distinguishes stable from unstable fractures based on posteromedial comminution 4
- Boyd-Griffin classification: Historical system with limited current utility 4
The Evans classification specifically identifies unstable patterns that, when combined with osteoporosis (Singh index), predict failure rates exceeding 50% with sliding hip screw fixation. 4
Clinical Application of Classification
The critical distinction is stable versus unstable fracture patterns, as this directly determines surgical management:
- Stable intertrochanteric fractures: Either sliding hip screw or cephalomedullary device is appropriate (strong recommendation) 3, 5
- Unstable intertrochanteric fractures: Cephalomedullary nail is mandatory (strong recommendation) 3, 5
- Subtrochanteric or reverse obliquity fractures: Cephalomedullary device is required (strong recommendation) 3, 5
Key Features Defining Instability
Unstable patterns requiring intramedullary fixation include:
- Comminuted fractures with posteromedial bone loss 5
- Reverse obliquity patterns 3, 5
- Subtrochanteric extension 3, 5
- Significant posteromedial comminution 5
Common Pitfall
The new AO classification shows that orthopedic residents achieve better inter-observer agreement (k = 0.388) than hip subspecialists (k = 0.109), suggesting that experienced surgeons may overcomplicate classification or rely on gestalt rather than systematic criteria. 1 Use the structured AO criteria consistently rather than pattern recognition alone to avoid misclassification that could lead to inappropriate implant selection.