MODELING STUDY OF COMPENSATORY HEAD MOVEMENTS IN LAME HORSES

Objective-To study the role of head movements in lame horses. Sample P opulation-11 Dutch Warmblood horses. Procedure-A 2-segment 2-dimension al inverse dynamic model of trotting horses was developed: trunk and h ead/neck segment joined in a neck joint. Model input consisted of aver aged segmental inertial properties and averaged kinematic data, taken from 11 horses, trotting on a treadmill (3.5 m/s) in 3 conditions of i nduced lameness. sound, mildly lame, and moderately lame. Dynamic and static effects were analyzed. Results-Dynamic effects were found to be considerably larger than static effects. In the moderately lame condi tion, the maximal neck joint vertical force during the lame stance pha se had a 27% decrease, compared with the sound situation. Neck joint s agittal torque and maximal vertical force on the trunk decreased by 31 and 13%, respectively. Load distribution between forelimb and hind li mb indicated a relative load shift from the lame forelimb to the diago nal hind limb during the lame stance phase. The sound contralateral fo relimb carried a higher load while the ipsilateral hind limb was unloa ded. Conclusion-It could be concluded that asymmetric head movements h ave a major role in lameness compensation, which can be explained by i nertial interaction between trunk and head/neck segment. Static effect s, such as caudad shifting of the body center of mass, are of minor im portance. Clinical Relevance-This report clarifies the mechanism of la meness compensation and the method of lameness diagnosis.