['It is known that posterior malleolar fracture is often associated with tibial diaphyseal fractures. However, in literature there are very few studies on tibial shaft fractures with respect to posterior malleolus fragment. We hypothesized that the incidence of posterior malleolar fracture is higher than in previous studies.', 'A total of 74 closed tibial shaft fractures were treated with intramedullary nailing in Turku University Central Hospital between January 1994 and December 1998. There were 55 men and 19 women, with a mean age of 39 years (range, 16 to 58 years). Two cases were excluded and 72 tibial shaft fractures were analyzed retrospectively.', 'Posterior malleolar fracture was observed in 18 cases (25.0%). Only 10 were observed preoperatively in plain films, seven were detected postoperatively and one was not detected at all during the treatment. Retrospectively, all 18 posterior malleolar fractures were detectable in preoperative plain films.'] Is posterior malleolar fracture often associated with spiral tibial diaphyseal fracture : a retrospective study?