Modeling study of compensatory head movements in lame horses.

Objective: To study the role of head movements in lame horses.

Methods: 11 Dutch Warmblood horses. Methods: 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.

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