[Movement analysis in the horse with special attention for the problem of skin displacement]

Kinematic gait analysis is a rapidly growing field of veterinary research promising to become even more important in coming years. All modern analytical techniques are based on the use of skin markers and are therefore prone to suffering from a biological error caused by the sliding of the skin over the underlying skeletal structures. To investigate this error skin displacement was quantified at 18 relevant sites using techniques designed to ensure simultaneous visualization of skin and underlying bone. Mathematical models for correction of skin displacement were formulated. Application of these models to a kinematic analysis of the reciprocal apparatus showed that the marked discrepancy between in vivo and in vitro measurements previously reported was almost entirely due to the artifact caused by skin displacement. It is concluded that correction for skin displacement is of the utmost importance in basic biomechanical research, but is not required in clinical kinematic analysis in every case.