AO/OTA classification of proximal femoral fractures

Last revised by Dr Joachim Feger on 18 Oct 2021

The AO/OTA classification is one of the most frequently used systems for classifying proximal femoral fractures or proximal femoral end segment fractures. Like other fractures, they are divided into three groups subject to the severity and complexity of the respective injury 1:

  • type A: trochanteric fracture (below the intertrochanteric line and above the inferior border of the lesser trochanter)
    • A1: simple pertrochanteric fracture
      • A1.1 isolated trochanter fracture: greater or lesser trochanter
      • A1.2 two-part fracture
      • A1.3 lateral wall intact (lateral wall thickness ≥20.5 mm*)
    • A2: multifragmentary pertrochanteric fracture/incompetence of the lateral wall (thickness≤20.5 mm*)
      • A2.2 one intermediate fragment  
      • A2.3 two or more intermediate fragments
    • A3: intertrochanteric or reverse oblique fracture
      • A3.1 simple oblique fracture
      • A3.2 simple transverse fracture
      • A3.3 wedge fracture or multifragmentary fracture
  • type B: femoral neck or subcapital femoral fracture (below the articular cartilage of the femoral head and above the intertrochanteric line)
    • B1: subcapital fracture
      • B1.1 valgus impacted
      • B1.2 nondisplaced
      • B1.3 displaced
    • B2: transcervical fracture (Pauwels 1-3: <30°, 30-70°, >70°)
      • B2.1 simple​
      • B2.2 multifragmentary
      • B2.3 shear fracture
    • B3: ​basicervical fracture
  • type C: femoral head fracture (articular fracture)
  • C1: split fracture
    • C1.1 ligamentum teres avulsion
    • C1.2 infrafoveal split fracture
    • C1.3 suprafoveal split fracture
  • C2: depression fracture
    • C2.1 depression with chondral lesion
    • C2.2 depression impaction fracture
    • C2.3 split depression fracture

*The lateral wall thickness is measured as the distance between fracture and a reference point on an anteroposterior x-ray 3 cm below the innominate tubercle of the greater trochanter angled 135° upwards.

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