Quantification of skin marker movement at the malleoli and talar heads.

BACKGROUND: Quantifying subtalar joint kinematics during locomotion is a major challenge but is critical to understanding foot function. The difficulty of modeling the subtalar joint is demonstrated by the plethora of three-dimensional multisegment foot models lacking specific consideration of the subtalar joint. Scientific attempts to develop an adequate method of quantifying subtalar joint kinematics should include investigation of the movement of skin-mounted markers. This study reports on a single-subject investigation into this topic.

METHODS: Radiopaque markers were attached to the skin overlying the medial and lateral malleoli and the medial and lateral talar heads of a single subject. Frontal, sagittal, and transverse plane radiographs were taken with the foot in the fully pronated and fully supinated positions. Parallax corrected measurements were taken of the displacement of the markers from the bony landmarks. Measurements were also taken of the effect of these displacements on angular calculations.

RESULTS: Skin movement at the four anatomical locations was not uniform, with displacements varying from 0.61 to 22.18 mm. Movement of the malleolar markers was found to be less than that of the talar head markers. The distortion of angular measurements caused by movement of the skin markers relative to the bony landmarks was found to be only 1° in the sagittal and transverse planes and 5° in the frontal plane.

CONCLUSIONS: For this subject, skin-mounted markers could be used to assess subtalar joint motion. Further studies are necessary to investigate the implications of these findings to the wider population.