TIBIOCALCANEAL MOTION DURING RUNNING, MEASURED WITH EXTERNAL AND BONEMARKERS

Objective. The purpose of this study was to compare tibiocalcaneal mot ion during running based on skeletal markers with tibiocalcaneal motio n based on external markers. Design. In vivo measurements of external and skeletal tibiocalcaneal kinematics. Background. External (shoe, sk in) markers are typically used to determine rearfoot kinematics. Howev er, it is not known if such markers are able to provide a good represe ntation of the skeletal (tibiocalcaneal) kinematics. Methods. Bone pin s were inserted into the tibia and calcaneus of five subjects. The 3-D motion of markers attached to bone pins as well as of external marker s attached to the shank and shoe were determined during the stance pha se of five running trials. Intersegmental motion was expressed in term s of Cardan angles (plantarflexion/dorsiflexion, abduction/adduction, inversion/eversion). Results. It was found that the skeletal inversion /eversion, abduction/adduction, and plantarflexion/dorsiflexion motion s were similar across the subjects. The shape of the tibiocalcaneal ro tation curves based on external markers were similar to those based on bone markers. However, the rotations were generally overestimated whe n using external markers, e.g. the average maximal eversion motion cal culated from external markers was 16.0 degrees whereas the skeletal ma ximal eversion motion was only 8.6 degrees. These discrepancies were m ainly due to the relative movement between shoe markers and underlying calcaneus. Conclusions. External markers are only gross indicators of the skeletal tibiocalcaneal motion. The rotations derived from extern al shoe and shank markers typically overestimate the skeletal tibiocal caneal kinematics.