Ankle fractures

Last evidence check Nov 2013

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 classified ankle fractures on the basis of

Weber (and hence AO) classified fractures according to the relation of the fibular fracture to the syndesmosis:

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:

  • Several biomechanical studies have attempted to reproduce the work and classification of Lauge-Hansen. Unfortunately, the fractures they produced did not correspond with Lauge-Hansen’s classification. (Michelson 1997, Haraguchi 2009). If anything, the fracture patterns produced by a given force in modern experiments tend to be less severe than those described by Lauge-Hansen, and the relationship between forces exerted on the ankle and fracture patterns is not exact.
  • Gardner (2006) and Hermans (2011) carried out MRI on a group of displaced ankle fractures, and Hermans compared the MRI with plain radiography. 10% could not be classified according to the Lauge-Hansen system. Over 50% did not have the patterns of ligament and bony injury predicted by their apparent Lauge-Hansen type.
  • The AO classification is more reproducible. This may not be a very useful advantage, however, as this finding relates only to the first level of both classifications. If one compares the second level (the level at which stability is considered in the AO classification) the reproducibility of both is very poor.
  • 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.