A occult and regular combination injury: the posterior malleolar fracture associated with spiral tibial shaft fracture.

Purpose: It is known that tibial diaphyseal fractures are often associated with the posterior malleolar fracture (PMF). There are a few studies on tibial shaft fractures with respect to posterior malleolus fracture. However, we found that the incidence of PMF was higher than the previously reported.
Methods: A total of 288 tibial shaft fractures were studied to analyze posterior malleolar in the Third Hospital of Hebei Medical University between January 2005 and June 2007. From June 2007, computed tomography (CT) scan or magnetic resonance imaging (MRI) was routinely performed in the ankle region, whereas the distal third spiral tibial fracture was found in the primary plain X-ray films.
Results: The PMF was found in 28 cases (9.7% of 288 cases). Only nine cases were observed preoperatively in plain X-ray films, four cases were detected intraoperatively, and 15 cases were not detected at all during the treatment. In the retrospective study, three PMF of 34 tibial shaft spiral fractures was detected in plain films, 23 PMFs detected by CT, and 4 PMFs detected by MRI. In four cases, there was no PMFs.
Conclusion: Spiral fractures of the distal tibia commonly have an associated occult posterior malleolus fracture. Even the careful radiographic examination of the ankle joint, that is mandatory before surgery, may not detect this injury. CT scan or MRI may be a compensative method to detect these injuries. CT scan should be routinely performed in clinical practice.