NONLINEAR DYNAMIC STABILITY OF NORMAL AND ARTHRITIC GREYHOUNDS

In this paper the dynamic stability of greyhound gait was analyzed wit hin the framework of nonlinear dynamics theory. A video based motion a nalysis system was utilized to obtain the kinematic data of the hindli mb joints of greyhounds at trot. Phase plane portraits and first retur n maps for the coxofemoral, femorotibial, and the tarsal joints were c alculated from averaged kinematic data for each dog. The analysis was based on the assumption that the steady state dog locomotion could be represented as a nonlinear periodic system. Using the Floquet theory, the dynamic stability of gait was quantified by computing the characte ristic multipliers from experimental data. A stability index based on multipliers was used for comparison between normal and arthritic dogs. Phase plane portraits and first return maps of the dogs with transien t synovitis were compared with the averaged portraits of the normal do gs. It was observed that the coxofemoral angle exhibited the maximum d ifference while the femorotibial and the tarsal joints showed little o r no difference from those of the normals. Comparison of the Floquet m ultipliers indicated that the dogs with synovitis had a less stable ga it than that of the normal dogs.