Quantification of skin marker movement at the malleoli and talar head

BACKGROUND:Quantifying subtalar joint (STJ) kinematics during locomotion is a major challenge, but critical to understanding foot function. The difficulty of modelling the STJ is demonstrated by the publication of a plethora of 3D multisegment foot models lacking specific consideration of the STJ. Any scientific attempt to develop an adequate method of quantifying STJ kinematics should include the investigation of movement of skin mounted markers. This study reports on a single subject investigation into this topic. METHODS:Radio opaque markers were attached to the skin overlying the medial and lateral malleoli, and medial and lateral talar head of a single subject. Frontal, sagittal and transverse plane x-rays were taken with the foot in a fully pronated and fully supinated position. Parallax corrected measurements were taken of the displacement of the markers from the boney landmarks. Measurements were also taken of the effect of these displacements on angular calculations. RESULTS:The skin movement at the four anatomical locations was not uniform, displacements varying from 0.61mm to 22.18mm. The movement of the maleolar markers was found to be less than that of the talar head markers. The distortion of angular measurements caused by the movement of the skin markers relative to the bony landmarks was found to be only 1o in the sagittal and transverse planes and 5o in the frontal plane. CONCLUSIONS:The results suggest that for this subject skin mounted markers could be used to assess STJ motion. Further studies are necessary to investigate the implications of the fidings to the wider population.status: publishe