THE RELATIVE SKIN MOVEMENT OF THE FOOT - A 2-D ROENTGEN PHOTOGRAMMETRY STUDY

Objective. This paper describes a validation of the relative motions o f skin-mounted markers on the foot. Design. The movement of a skin-mou nted marker on the foot was evaluated by the use of 2-D roentgen photo grammetry. Background. Validations of skin-mounted markers are needed in order to assess whether clinical use of motion analysis systems is accurate. Methods. Six healthy volunteers participated in the study. M easurements were made with 2-D roentgen photogrammetry from the medial aspect of the foot. Spherical lead markers, with a diameter of 2 mm, were glued on the skin over the following landmarks: the medial malleo lus, the navicular bone, the medial part of calcaneus, the base and th e head of the first metatarsal bone, and the base of the fifth metatar sal bone. The foot was placed on a platform that was adjustable in thr ee directions: horizontal, 20 degrees upward (towards dorsal flexion), and 30 degrees downward (towards plantar flexion). Results. In relati on to the underlying bones, the markers were found to move up to 4.3 m m. The markers with the largest movements were the ones over the media l malleolus, the navicular bone and the calcaneus. For the distally pl aced markers i.e. at the base and the head of the first metatarsal bon e, and the base of the fifth metatarsal bone, the displacements were a maximum 1.8 mm. Conclusions. Markers mounted on the foot moved betwee n 1.8 and 4.3 mm corresponding to the underlying bones. The most proxi mal attached markers demonstrated the largest movements. Relevance As opto-electronic measuring systems are getting more common, not only fo r research, but also for clinical purposes, the accuracy of the measur ing technique must be assessed. (C) 1998 Elsevier Science Ltd. All rig hts reserved.