Sagittal ankle position does not affect axial CT measurements of the syndesmosis in a cadaveric model.

BACKGROUND: The purpose of this study was to evaluate the effect of ankle plantarflexion and the axial location of measurement on quantitative syndesmosis assessment.

METHODS: Twelve fresh-frozen cadaveric specimens were secured in three positions of ankle plantarflexion (0°, 15°, and 30°) using an ankle-spanning external fixator and underwent CT scans at each position. Syndesmotic measurements were obtained on axial images using three previously described methods (six measurements) at the level of the tibial plafond and 1 cm proximal to the plafond. Method 1 evaluated the distance between the most anterior and posterior aspects of the fibula and tibia. Method 2 measured medial-lateral diastasis of the anterior and posterior aspects of the fibula, and fibular anterior-posterior translation. Method 3 evaluated axial rotation of the fibula. All measurements were performed by two independent observers. Inter-rater reliability of each measurement was evaluated using intra-class coefficients. Repeated measures analysis of variance (RM-ANOVA) was performed to evaluate within-specimen differences in measurements obtained at varying ankle positions.

RESULTS: The anterior incisura component of method 1 demonstrated poor-to-moderate inter-rater reliability across all ankle positions and at both measurement locations. Inter-rater reliability was highest for method 2, especially when measured 1 cm proximal to the plafond. Method 3 demonstrated moderate reliability 1 cm proximal to the plafond. After correcting for multiple comparisons, RM-ANOVA and pairwise analysis revealed that none of the measurements changed significantly with varying ankle position.

CONCLUSION: The inter-rater reliability of the most common method of syndesmotic evaluation (method 1) was found to be lower than in previous studies. The most reliable syndesmotic evaluation can be made by measuring diastasis and anteroposterior translation 1 cm proximal to the plafond (method 2). Ankle position from 0° to 30° of plantarflexion did not change the measurements obtained.

LEVEL OF EVIDENCE: IV.