The biomechanical model suggests that the most important axis of classification is stability rather than fracture morphology or displacement in themselves. This is supported by a meta-analysis of both bio- mechanical and clinical literature (Michelson 2007). Neither of the existing major fracture classification systems gives enough weight to stability, and both have additional problems.
These two classifications, which are somewhat related, are:
- Lauge-Hansen (1950)
- Weber, which was largely taken over by the AO group
Lauge-Hansen classified ankle fractures on the basis of
- The position of the foot at the time of injury. In a closed-chain environment, a pronated foot will result in tight medial and lax lateral ligamentous structures and a supinated foot will result in tight lateral and lax medial structures
- The direction of the force applied to the ankle: adduction, abduction or external rotation. Lauge-Hansen indicated that this force determined the order in which structures fail, and that structures fail in a predictable order.
Weber (and hence AO) classified fractures according to the relation of the fibular fracture to the syndesmosis:
- Type A below
- Type B at the level
- Type C above
In the AO version, there are two sub-layers of the classification, giving classifications such as B1 (later- al malleolus fracture at the level of the syndesmosis, medial structures intact) or B2 (lateral malleolus fracture at the level of the syndesmosis, medial structures failed).
How good are the classifications?
It appears initially that the Lauge-Hansen classification is more what we are looking for. In particu- lar, supination-external rotation injuries would be stable until the medial structures fail, detaching the DDL from the tibia, while pronation injuries would always be instable as the medial structures fail first. Instability is at the first, fundamental level of the classification while in the AO classification it is at the second level.
Unfortunately, there are a number of problems with Lauge-Hansen’s classification:
Probably we need a new approach to classification which fits with the biomechanical, imaging and clinical evidence better, is focused on stability and is reproducible at a level that matters. The Hyperbook strongly supports the quest for a more scientifically sound classification (Michelson 2007). The Hyperbook groups fractures according to stability. However, we also consider the existence of a group of fractures which are potentially unstable because they have a medial injury, but which are undisplaced at presentation.