Deltoid ligament integrity in lateral malleolar fractures: a comparative analysis of arthroscopic and radiographic assessments

Foot and ankle surgeons often rely on the medial clear space to evaluate competency of the deep deltoid ligament when evaluating ankle fractures. This investigation assesses the integrity of the deep deltoid ligament after lateral malleolar fracture by using direct arthroscopic visualization and medial clear-space separation on plain film radiographs. The objectives of this study were to test the reliability of medial clear-space separation and the Lauge-Hansen classification scheme in predicting deep deltoid rupture in displaced lateral malleolar fractures. The medial clear space was measured on injury radiographs of 40 patients with an isolated displaced lateral malleolar fracture who underwent open reduction and internal fixation. Injury radiographs were classified according to the Lauge-Hansen scheme. Direct arthroscopic visualization was used to evaluate the deep deltoid ligament under manual stress before fracture reduction. The mean preoperative medial clear space in patients with a deep deltoid rupture (n = 13) was 6.6 +/- 2.4 mm (range, 4 to 12 mm), and in patients without a deep deltoid rupture (n = 26), it was 4.0 +/- 1.0 mm (range, 2.5 to 6 mm) (P =.002, 2-sample t test). At an injury medial clear space > or =3 mm, the false positive rate for deltoid rupture was 88.5% (P =.54, Fisher's exact test). At > or =4 mm, the false positive rate was 53.6% (P =.007). All fractures were rotational injuries according to the Lauge-Hansen system. Three fractures were not classifiable; another 3 fractures showed deltoid ligament integrity opposite the expected finding. The results indicate that, in isolated displaced fractures of the lateral malleolus, radiographic widening of the medial clear space is not a reliable indicator for deep deltoid rupture. Some fractures considered stable by the Lauge-Hansen classification may require careful scrutiny to rule out deep deltoid injury.