106. A CLINICALLY RELEVANT CLASSIFICATION OF POSTERIOR MALLEOLUS FRACTURES TO GUIDE IMAGING AND TREATMENT

Abstract

Purpose: Lower extremity articular fracture treatment requires acccurate diagnosis and anatomic reduction and fixation. As articular injuries, posterior malleolus (PM) fractures are still poorly defined: for example the incidence of associated PM marginal impaction and of free articular fragments is unknown. The purposes of this study were:

1. to define the articular injuries of PM fractures into clincially relevant groups, as complex articular injuries could require specific surgical steps;

2. to identify clinical and radiographic parameters which would alert the surgeon to the presence of complex injuries.

Method: Our prospectively-collected orthopaedic trauma database (OTDB) query identified 796 ankle fractures treated operatively between 2003–2007. Of these 147 cases involved the posterior malleolus. Four were misclassified leaving 143 cases. We obtained demographic and injury data from the OTDB, and validated the OTDB coded mechanisms of injury by an individual chart review. We reviewed all radiographs to describe the PM injuries (fracture patterns and dimensions) and to identify the associated injuries.

Results: Of the 143 cases: Mean age was 50 years (sd=19), 68.5% were female, 51% were right sided injuries, and the median ISS=4 (in fact, 97.5% had ISS=4, most therefore being isolated trauma). The mean post malleolus AP size=11mm (sd=5). We identified recurrent patterns and classified the PM fracture as SIMPLE or COMPLEX (to include marginal impaction or free comminuted fragment, which should be anatomically reduced), 42% of cases (60/143) were COMPLEX (18 were impaction, 42 were free fragment). To help clinicians identify which cases could be COMPLEX we correlated (Chi-sq) the presence of a COMPLEX PM fracture to common clinical and radiographic variables. COMPLEX PM were statistically significantly associated with (p values)

1. an axial loading injury mechanism (.000),

2. a radiographically captured dislocation (.006),

3. posteromedial comminution [as defined Tor-netta] (.005)

4. the size of the fragment (.000).

For example, axial loading would result in a complex fracture in > 85% of cases. In contrast, there was a statistically significant association between a Weber C fracture and older age and the presence of a SIMPLE PM fracture. These factors being potentially “protective” from joint comminution.

Conclusion: We have defined and quantified the PM articular lesions which require anatomic reduction and fixation, beyond what has been published. We have defined clinical and radiographic criteria which, because higly associated with COMPLEX lesions, could

1. prompt surgeons to order further imaging (CT) to better delineate the lesion, and

2. draw his/her attention to potentially malaligned fragments at the time surgery.