OBJECTIVETo analyze causes of missed diagnosis of hiding post-malleolar fractures in treating ankle joint fractures of pronation-external rotation type according to Lauge-Hansen classification and assess its medium-term outcomes.

METHODSAmong 103 patients with ankle joint fracture of pronation-external rotation type treated from March 2002 to June 2010,9 patients were missed diagnosis,including 6 males and 3 females,with a mean age of 35.2 years old (ranged, 18 to 55 years old) . Four patients were diagnosed during operation, 2 patients were diagnosed 2 or 3 days after first surgery and 3 patients came from other hospital. All the patients were treated remedially with lag screws and lock plates internal fixation. After operation,ankle joint function was evaluated according to American Orthopaedic Foot and Ankle Society (AOFAS).

RESULTSAll the 9 patients were followed up, and the duration ranged from 14 to 30 months (averaged, 17 months). No incision infection was found, and all incision healed at the first stage. At the latest follow-up, AOFAS was 83.0 +/- 4.4, the score of 4 patients diagnosed during operation was 85.0 +/- 2.9, and the score of 5 patients treated by secondary operation was 81.0 +/- 5.3. All the patients got fracture union observed by X-ray at a mean time of 2.2 months after operation. There were no complications such as internal fixation loosing, broken and vascular or nerve injuries.

CONCLUSIONAnkle joint fracture of pronation-external rotation type may be combined with hiding post-malleolar fractures. So to patients with ankle joint fracture of pronation-external rotation type, lateral X-ray should be read carefully, and if necessary, CT or MRI examination should be performed. If adding lateral X-ray examination after reduction of exterior and interior ankle joint fixation, the missed diagnosis may be avoided.