Posterior Malleolar Fragment Size as a Predictor of Ligamentous Injuries in Trimalleolar and Quadrimalleolar Ankle Fractures: A Novel Correlative Cohort Study in a South Indian Population.

Abstract

Background: Posterior malleolar (PM) fractures are critical components of complex ankle injuries, particularly in tri- and quadrimalleolar fracture patterns. Although traditionally assessed by fragment size and displacement, emerging evidence suggests a more intricate relationship between PM morphology and associated ligamentous injuries. Aim was to evaluate the association between PM fragment size and concomitant soft tissue injuries, particularly deltoid and syndesmotic involvement in tri- and quadrimalleolar ankle fractures.

Methods: This ambispective cohort study included 45 adult patients with tri- or quadrimalleolar fractures treated via a posterolateral approach. PM fragments were classified using computed tomography-based systems (Haraguchi, Bartonicek-Rammelt, Mason-Molloy). The presence of ligamentous injuries was assessed intra-operatively and correlated with fragment size. Syndesmotic and deltoid ligament involvement were analysed in relation to PM morphology. Statistical analysis was performed using SPSS version 22.

Results: Most PM fractures were Haraguchi type 1 (66.7%), Bartonicek-Rammelt type 2 (62.2%), and Mason-Molloy type 2A (60%). Although syndesmotic injury showed no statistically significant association with PM fragment size (P = .135), a novel finding was identified: PM fragments larger than 8 mm were significantly associated with deltoid ligament injuries (P = .01). This correlation suggests a potential predictive role of fragment size in identifying medial-sided instability.

Conclusion: Posterior malleolar fragment size, particularly fragments exceeding 8 mm may serve as a surrogate marker for deltoid ligament injury in tri- and quadrimalleolar ankle fractures, whereas no significant association was identified with syndesmotic injury. This finding highlights the importance of comprehensive pre-operative imaging and intra-operative assessment to guide fixation strategies and address associated ligamentous pathology.

Level of evidence: Level III, evidence from non-experimental descriptive studies.