Objective: Classification of malleolar fractures is a matter of debate. In the ideal situation, a classification system is easy to use, shows good inter- and intraobserver agreement, and has implications for treatment or research.
Material and methods: Interobserver study. Four observers distributed 100 X-rays to the Weber, AO and Lauge-Hansen classification. In case of a trimalleolar fracture, the size of the posterior fragment was measured. Interobserver agreement was calculated with Cohen's kappa. Agreement on the size of the posterior fragment was calculated with the intraclass correlation coefficient.
Results: Moderate agreement was found with all classification systems: the Weber (K = 0.49), AO (K = 0.45) and Lauge-Hansen (K = 0.47). Interobserver agreement on the presence of a posterior fracture was substantial (K = 0.63). Estimation of the size of the fragment showed moderate agreement (ICC = 0.57).
Conclusion: Classification according to the classical systems showed moderate interobserver agreement, probably due to an unclear trauma mechanism or the difficult relation between the level of the fibular fracture and syndesmosis. Substantial agreement on posterior malleolar fractures is mostly due to small (<5 %) posterior fragments. A classification system that describes the presence and location of fibular fractures, presence of medial malleolar fractures or deep deltoid ligament injury, and presence of relevant and dislocated posterior malleolar fractures is more useful in the daily setting than the traditional systems. In case of a trimalleolar fracture, a CT scan is in our opinion very useful in the detection of small posterior fragments and preoperative planning.