A Simplified, Validated Protocol for Measuring Fibular Reduction on Ankle CT

Background: Inadequate ankle syndesmotic reduction is a common and important cause of poor outcome after surgery. It is not clear what magnitude or planes of displacement impact most. Many computerised tomography (CT) measurement techniques rely on landmarks that are difficult to reproduce, and none measure all types of mal-positioning in a single protocol. The purpose of this study was to design and validate a protocol for measuring the distal tibio-fibular relationship.

Methods: We devised a method for measuring fibular diastasis, antero-posterior translation (APT) and fibular length on CT images. CTs of sixteen un-injured ankles were examined using our protocol and that of an established alternative method for comparison. The measurements were recorded by two independent observers and repeated for inter- and intra-observer agreement scores.

Results: Our method showed inter- and intra-observer agreement of r=0.994 and r=0.999, demonstrating strong agreement. This compared to r=0.218 and r=0.820 respectively for the comparative protocol.

Conclusion: This ankle CT measurement protocol is accurate, reproducible and simple to use. Its aim is to be a useful tool for clinicians to quantify post-operative mal-positioning of the distal fibula in comparison to the un-injured ankle. We believe that routine, bilateral, post-operative CT imaging will lead to improvements in the understanding and outcomes of the treatment of complex ankle fractures. To our knowledge no other validated measurement of fibular length on CT images exists in the literature.