Does Foot Position and Location of Measurement Influence Ankle Medial Clear Space?

PURPOSE: There is still controversy regarding normal and abnormal values of the medial clear space (MCS) of the ankle. The aim of this study was to assess how much different degrees of plantar flexion, with and without stress, influenced the MCS.

METHODS: We submitted 30 volunteers to 6 different anteroposterior ankle radiographs in the following positions: neutral, neutral with external rotation stress, physiologic plantar flexion (FPF), physiologic plantar flexion with external rotation stress, maximum plantar flexion (MPF), and maximum plantar flexion with external rotation stress. The MCS oblique (MCSo) and perpendicular (MCSp) were measured in all images by an experienced foot and ankle surgeon.

RESULTS: The data showed that the position of the foot does influence the value of MCSp and MCSo ( P < .05), except for 3 comparisons. MCSo did not change between FPF with stress and MPF with stress. MCSp did not change in 2 situations: between FPF and neutral with stress and between MPF and FPF with stress.

CONCLUSIONS: This study is unique in showing that different ways of positioning the foot and performing stress radiographs results in different MCS values and that these values differ depending on the anatomical site where they are measured.

LEVELS OF EVIDENCE: Diagnostic, Level IV.