Quantitative Analysis of Talar Dome Morphology

CATEGORY: Ankle; Other INTRODUCTION/PURPOSE: A flat-top talar dome deformity can alter ankle mechanics and impact daily activities. Radiographic determination of flatness is difficult using traditional measures. The purpose of this study is to describe a new method to quantify the talar dome morphology using lateral radiographs and a custom-written image processing algorithm. METHODS: Skeletally mature patients previously treated for idiopathic clubfeet were identified from our institution’s clubfoot registry. All patients had weight-bearing lateral foot radiographs. Measurements included radius of curvature (ROC) of the talar dome and tibial plafond, talar length and height, and alpha angle. The ratio of the radii of the talar dome and tibial plafond (TD/TP Ratio) was determined. Custom-written, image processing MATLAB code was used to identify the talus from the lateral radiograph. Following manual identification of the articular surface, the average slope of the anterior, central, and posterior regions of the talar dome were calculated. Talar dome flatness was determined as the slope variance across all three regions. Higher variance indicated a rounder talar dome morphology, lower variance indicated a flatter dome. Inter-rater reliability of radiographic measures and the MATLAB based talar dome flatness were determined. Spearman’s rho was used to determine correlations between radiographic and MATLAB flatness measures. RESULTS: For radiographic measures, the Inter-rater reliability (IRR) was determined for 52 feet. IRR was near perfect for the ROC of the talar dome (ICC=.985), talar length (ICC=.952), and alpha angle (ICC=.928). Measurement of the radius of the tibial plafond (ICC=.827) and talar height (ICC=.893) were reproduced with excellent reliability. The IRR of the TD/TP ratio was moderate (ICC=.608). Preliminary IRR for the MATLAB-based talar dome flatness (15 feet) was excellent (ICC=0.895). Flatness was strongly correlated with ROC of the talar dome (r=.621, p=.013), alpha angle (r=.557, p=.031) and TD/TP Ratio (r=-.589, p=.021). CONCLUSION: Flatness of the talar dome can be difficult to describe, as there lacks a single measure to accurately define its morphology. The method developed in this study was quick to apply (less than 5 to 10 minutes per foot) and had high inter-rater reliability.