Mechanical failure after primary internal fixation of unstable ankle fractures -A retrospective observational study.

Background: Ankle fractures are common injuries treated by trauma surgeons. Failure of fixation necessitating subsequent revisions remains a significant concern, carrying increased morbidity and healthcare cost. Mechanical failures are poorly categorised in the literature. This study aims to classify patterns of mechanical failure following primary ankle internal fixation.

Methods: A retrospective observational study was conducted at a single major trauma centre, reviewing electronic patient records (EPR) and radiographs of 897 patients who underwent internal fixation for unstable ankle fractures over five years (June 2014 to August 2018). Data on patient demographics, injury characteristics, surgical techniques, and complications were collected. Mechanical failures were categorised into three subtypes based on the direction of talar displacement and syndesmotic involvement: Type 1 (lateral talar instability with intact syndesmosis), Type 2 (lateral talar instability with disrupted syndesmosis), and Type 3 (posterior talar instability). The inter-rater reliability of this classification system was evaluated using intraclass correlation coefficient (ICC) analysis.

Results: The revision rate after primary ankle internal fixation was 6.6 % (59/897), with mechanical failures accounting for 69 % (41/59) and infective failures for 31 % (18/59). Patients in whom the primary ankle fixation failed were significantly older than the group in whom the primary ankle fixation did not fail (mean age 60 vs. 52 years, p = 0.0018). The mean ICC values for the classification system was 0.84, indicating good inter-rater reliability.

Conclusions: The revision rate for unstable ankle fractures treated with primary internal fixation was 6.6 %, with the majority of revisions attributed to mechanical failures. Lateral talar instability, particularly when associated with syndesmotic disruption, was the most common cause of mechanical failure. Our grading system demonstrated high inter-rater reliability and provides a tool for categorising these failures.