The Use of the Lateral Tibial Line to Assess Ankle Alignment: A Preliminary Investigation

Category: Ankle; Trauma Introduction/Purpose: Although the medial clear space (MCS) is commonly used to assess talar alignment and ankle stability, its measurement is variable with multiple reported “normal” values. We have observed that the lateral tibial shaft is a reliable landmark to assess talar alignment. The objective of the current investigation was to determine the normal relationship of the lateral tibia to the superolateral talus using a tangent drawn inferiorly from the lateral tibial shaft, which we refer to as the “lateral tibial line” (LTL). Methods: The relationship of the LTL to the superolateral talus was assessed and characterized on ninety-nine standing ankle mortise radiographs in uninjured patients. This relationship was quantified by measuring the distance (in millimeters) between the LTL and the superolateral talus. Additionally, the inter-observer reliability of the LTL measurement, determined by three reviewers, was recorded and compared to medial clear space measurements. Results: The median value for the lateral tibial line was -0.50 mm with an interquartile range of -1.4mm - 0.0mm. The LTL was within 1mm of the lateral talus in 176 of 297 reviewer measurements (59.3%). Moreover, it was either lateral to or was at most 1mm medial to the lateral talus in 90.9% of cases. The LTL measurement also demonstrated good inter-observer reliability (0.764, 95% CI: 0.670-0.834), similar to the measurement of MCS (0.742, 95% CI: 0.539-0.846). Conclusion: The LTL is easily measured with good reliability for assessing the anatomic relationship of the tibia and talus. It uncommonly fell more than 1 mm medial to the superolateral talus. In other words, it was uncommon for the talus to shift lateral to this line, as might be seen with displaced ankle fractures. These findings will hopefully serve as a standard for future studies evaluating the role of the LTL in assessing lateral displacement and stability of isolated fibula fractures.