Determination of the mechanical properties of the sacroiliac joint of a dog by imaging measurement methods and model update in a multi‐body model

Abstract The sacroiliac joint (SIJ) is the articulated connection between the sacrum and the ilium and is a tight, combined, and only slightly mobile joint. In many dogs, the joint becomes stiff with age. As a result, the animal experiences pain while moving. Too little information is known about the degree of stiffening and the physiological range of motion for therapy. Consequently, recording the range of motion of different individuals (healthy and diseased) is a step toward a better understanding of the SIJ syndrome. For the basic investigation of the mechanical properties of the SIJ, post‐mortem examinations are performed on different individuals. To determine the mobility of the joint, the sacrum is fixed and a movement is forced on the ilium using actuators and recording the required forces. In addition, the spatial movement of the ilium and sacrum is measured. The kinematic and dynamic variables can be used to determine the translational and rotational stiffness of the SIJ. As it is not possible to apply directed loads to the ilium, the measurement data is used to determine the elastic parameters of the joint ligaments using heuristic methods. The multi‐body model includes the ilium, the ligaments, and the actuators of the test rig with their spatial orientation.