The most commonly used classification system for Open fractures. Created by Ramon Gustilo and Anderson, then further expanded by Gustilo, Mendoza, and Williams.
This system uses the amount of energy, the extent of soft-tissue injury and the extent of contamination for determination of fracture severity. Progression from grade 1 to 3C implies a higher degree of energy involved in the injury, higher soft tissue and bone damage and higher potential for complications. Important to recognize that grade 3C fracture implies vascular injury as well.

Gustilo open fracture Classification

Gustilo type	Definition
I	Open fracture, clean wound, wound <1 cm in length
II	Open fracture, wound > 1 cm in length without extensive soft-tissue damage, flaps, avulsions
III	Open fracture with extensive soft-tissue laceration, damage, or loss or an open segmental fracture. This type also includes open fractures caused by farm injuries, fractures requiring vascular repair, or fractures that have been open for 8 h prior to treatment
IIIA	Type III fracture with adequate periosteal coverage of the fracture bone despite the extensive soft-tissue laceration or damage
IIIB	Type III fracture with extensive soft-tissue loss and periosteal stripping and bone damage. Usually associated with massive contamination. Will often need further soft-tissue coverage procedure (i.e. free or ratational flap)
IIIC	Type III fracture associated with an arterial injury requiring repair, irrespective of degree of soft-tissue injury.

There are many discussions regarding the inter-observer reliability of this classification system. Different studies show iner-observer reliability of approximately 60% (ranging from 42 to 92 %).

Another important issue of this classification system is the ability to predict outcome. For this purpose, other classification systems, like Mangled Extremity Severity score (MESS) and Limb Salvage Index (LSI) have been devised.