Summary

Weight bearing CT Distance, Area and Volumetric Measurements demonstrated only low/average diagnostic accuracy in detecting chronic subtle syndesmotic instability

Abstract

Introduction

Improving the diagnosis of subtle syndesmotic instability (SSI) represents one of the most challenging missions in orthopaedic surgery, since undiagnosed instability frequently leads to post-traumatic ankle arthritis. The advent of weight-bearing computed tomography (WBCT) brought hope for improved non-invasive SSI diagnosis, particularly by utilizing distal tibio-fibular syndesmotic (DTFS) area and volume measurements. The goal of this study was to prospectively evaluate the diagnostic accuracy of WBCT Distance Maps (DM), Area and Volumetric Measurements in Detecting Chronic Subtle Syndesmotic Instability. We hypothesized that WBCT measurements would demonstrate high diagnostic accuracy in detecting chronic subtle syndesmotic instability.

Methods

This is a prospective comparative diagnostic controlled study. We included patients who met the following criteria: chronic syndesmotic injury (>6 months), Normal tibiofibular clear space (<6mm), 18 years old or older, no hindfoot mal-alignment (0.6>Foot Ankle Offset <5.2), flexible hindfoot deformity (Progressive Collapsing Foot Deformity stage I) and those without major ankle arthritis changes (The Kellgren and Lawrence score =1). All included patients and controls underwent Foot/Ankle WBCT. We measured distance mapping, area and volume at 1,3 and 5 cm from the ankle joint. All patients with suspected syndesmotic instability underwent arthroscopic assessment/treatment (passage of 3 mm sphere in the tibio-fibular space at the syndesmosis while performing manual external rotation test confirmed syndesmotic instability).

Results

15 patients were included in the study and matched to 12 controls. Area measurements were most accurate at 1 cm proximal to ankle joint (70.4%) and less accurate at 3 cm and 5 cm (46.8% at both sites). Volume measurements were most accurate at 1 cm proximal to the ankle joint (66.2%) followed by measurements at 3 cm (62.5%), while the least accurate was measurement at 5 cm (56.5%).

Conclusion

WBCT Distance, Area and Volumetric Measurements demonstrated only low/average diagnostic accuracy in detecting chronic subtle syndesmotic instability. We found also that area measurement at 1cm and volumetric measurements at 1 and 3 cm proximal to the joint were to be the best diagnostic tools. Minimum syndesmotic distances, area measurements (1cm) and Volumetric measurements (1 and 3 cm) were significantly increased in the injured side in comparison to the contralateral non-injured side.