Modeling study of compensatory head movements in lame horses.

OBJECTIVE

To study the role of head movements in lame horses.

SAMPLE POPULATION

11 Dutch Warmblood horses.

PROCEDURE

A 2-segment 2-dimensional inverse dynamic model of trotting horses was developed: trunk and head/neck segment joined in a neck joint. Model input consisted of averaged segmental inertial properties and averaged kinematic data, taken from 11 horses, trotting on a treadmill (3.5 m/s) in 3 conditions of induced 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 condition, the maximal neck joint vertical force during the lame stance phase had a 27% decrease, compared with the sound situation. Neck joint sagittal torque and maximal vertical force on the trunk decreased by 31 and 13%, respectively. Load distribution between forelimb and hind limb indicated a relative load shift from the lame forelimb to the diagonal hind limb during the lame stance phase. The sound contralateral forelimb carried a higher load while the ipsilateral hind limb was unloaded.

CONCLUSION

It could be concluded that asymmetric head movements have a major role in lameness compensation, which can be explained by inertial interaction between trunk and head/neck segment. Static effects, such as caudad shifting of the body center of mass, are of minor importance.

CLINICAL RELEVANCE

This report clarifies the mechanism of lameness compensation and the method of lameness diagnosis.