Evaluation of a three-dimensional kinematic model of the hindlimb in dogs
Torres, Bryan Thomas
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Clinical kinematic studies have been underutilized in veterinary medicine. Previous studies have focused on hindlimb joint motion with respect to ﬂexion and extension utilizing a linear-link model to deﬁne sagittal plane motion; however, joint movement is complex and incompletely represented in a two-dimensional (2-D) model. While 2-D models provide accurate and repeatable information about uniplanar motion they are limited in their ability to assess true three-dimensional (3-D) joint motion. The Joint Coordinate System (JCS) was developed to describe 3-D joint motion by 6 independent coordinates or 6 degrees of freedom. Additionally, it facilitates the description and understanding of joint motion between biomechanical and clinical ﬁelds. The beneﬁt of a segmental rigid-body model, such as the JCS, is that it provides an anatomically accurate and clinically relevant 3-D description of joint motion with six degrees of freedom. These studies were performed to provide the initial description of a 3-D segmental rigid-body model of the hindlimb of the dog based on the JCS. Additionally, to compare this new 3-D model to previous 2-D models, and describe the effect of known sources of kinematic variability on this model. The results of the first study established that the new 3-D model produces similar sagittal plane kinematics to previously established 2-D models; while providing additional information regarding the transverse and frontal planes of joint motion. The second study found that changes in marker placement alter kinematic data similarly for the 3-D and 2-D models. For both models, the greatest degree of change was found when placement errors occurred in the craniocaudal direction. The third study established that inter- and intra-examiner variability occurs with the 3-D model. Similar findings have been shown with 2D models. However, experience with the 3D model reduced overall variability and resulted in consistent and repeatable sagittal plane kinematic data collection. The final study evaluated the effect of different modes of ambulation (overground versus treadmill) on the 3-D kinematic model. We found that while both modes produce similar gait waveforms, only sagittal plane data was unaffected by mode of ambulation.