AO Classification of bone fracture.

It is a system for classifying bone fractures initially by categorizing injuries according to their anatomy and functional outcome. A fracture is classified by creating a five element alphanumeric code (Example 13A1.4) indicating the following components:

Location of the fracture.

This part contains name of the bone and a segment at which the fracture is located.

Bone

This part describes a specific bone involved indicating Name of the involved bone in which each bone is represented by a specific number which is the first number in the alpha numeric code.

Segment

This describes a specific region on a bone in which fracture has occurred. It is represented by a second number on the alpha numeric code.

Morphology of the fracture pattern

This part describes type, group and sub group of the fracture site as described here below:

Type

This part represents a specific type of fracture as well as the fracture pattern of the born involved. It is recorded by using capital letters just after first two numbers of the 5 Alphanumeric code.

Group

It is represented by the first number after a letter in the alpha numeric code. For instance here below is the table showing groups for diaphyseal fractures:

		Group	
Type	1	2	3
A-Simple	Spiral	Oblique	Transverse
B-Wedge	Spiral	Bending	Multi fragmentary
C-Complex	Spiral	Segment	Irregular

Subgroups

The subgroups are assigned based on the list of universal modifiers which is the list of fracture morphology, displacement, associated injury, or location that are generalizable to most fractures. They provide details that are optional for users. It is represented as a last number in the alpha numeric in brackets or after a full stop mark.

List of universal modifiers
1		Nondisplaced
2		Displaced
3	3a 3b	Impaction Articular Metaphyseal
4		No impaction
5	5a 5b 5c 5d 5e 5f	Dislocation Anterior (volar, palmar, plantar) Posterior (dorsal) Medial (ulnar) Lateral (radial) Inferior (with hip is also obturator) Multidirectional
6	6a 6b 6c 6d 6e 6f	Subluxation/ligamentous instability Anterior (volar, palmar, plantar) Posterior (dorsal) Medial (ulnar) Lateral (radial) Inferior (with hip is also obturator) Multidirectional
7		Diaphyseal extension
8	8a 8b 8c 8d 8e	Articular cartilage injury fracture ICRS Grade 0 Normal ICRS Grade 1 Superficial indentation (A) and /or superficial fissures and cracks (B) ICRS Grade 2 Abnormal lesions extending down to 50% of cartilage depth ICRS Grade 3 (A) Severely abnormal with defects extending down >50% of cartilage depth; (B) down to calcified layer; (C) down to subchondral bone but not through; (D) blisters included ICRS Grade 4 Severely Abnormal Cartilage loss through subchondral bone
9		Poor bone quality
10		Replantation
11		Amputation associated with a fracture
12		Associated with a non arthroplasty implant
13		Spiral type fracture
14		Bending type fracture

Examples

12B2.2

1-Humerus, 2-Shaft, B-Wedge, 2-Bending, .2-displaced.

Displaced bending wedge fracture of humeral shaft

31C3.9

3-Femur, 1-Proximal, C-Complex, 3-Irregular, .9-Poor bone quality.

Complex irregular Fracture of proximal femur with poor bone quality.

21C2

2-Tibia/Fibula, 1-Proximal, C-Complex, 2-Segmental

Complex segmental fracture of proximal Tibia/Fibula