Ankle fractures with Chaput fragment: A new classification system with insights into morphology and relation to surgical treatment
Abstract
A morphological study proposing the Patel-Dhillon classification for the often-overlooked Chaput fragment (anterior tibial avulsion). The authors identify four distinct types and introduce FABER variants (Anterior/Lateral/Medial Trimalleolar) to guide fixation strategies.
Classifying the Fourth Malleolus
Key Finding
"The study identified Type 1 (small avulsion) as the most common variant (60.6%), which typically reduces indirectly without fixation, whereas Types 2-4 require rigid fixation due to high-energy axial loading mechanisms."
Background: The Chaput fragment is frequently cited but poorly understood. No dedicated classification system existed to describe its morphology or its role in the transitional zone between rotational ankle fractures and high-energy pilon fractures. This gap often leads to inconsistent management of the anterior syndesmotic attachment.
Methods: A retrospective analysis of 33 ankle fractures involving a Chaput fragment. The authors analyzed CT scans to develop the Patel-Dhillon Classification: Type 1 (Avulsion), Type 2 (Large Anterolateral Oblique), Type 3 (Medial Extension), and Type 4 (Comminuted). They also re-categorized trimalleolar fractures into FABER variants based on which three malleoli were involved.
Results: Type 1 fractures were predominant (60.6%) and were successfully managed conservatively or with suture anchors in 90% of cases. Conversely, Type 3 and 4 fractures represented high-energy pilon-variant injuries requiring buttress plating. The study also debunked the classical definition of trimalleolar fractures, describing Anterior Trimalleolar (Medial + Lateral + Chaput) and Medial Trimalleolar (Medial + Posterior + Chaput) patterns that demand fragment-specific approaches.
Conclusion: The Chaput fragment is a sentinel marker for injury energy. Small Type 1 fragments are benign rotational injuries, but Type 3/4 fragments signal a pilon-like axial load requiring aggressive plating. Surgeons must recognize the Anterior Trimalleolar variant to avoid missing the dominant anterior instability.