We report on four adult patients in whom intramedullary nailing of external rotation tibial shaft fractures resulted in significant intra-articular displacement of the posterior malleolus that required further operative fixation. An ankle injury was not recognized preoperatively in any case. Intramedullary nailing of certain tibial shaft fractures may be at risk for displacement of the posterior malleolus. The ankle joint should be examined very carefully not only preoperatively, but also intraoperatively in these cases.