Characterizing Healthy Sacroiliac Joint Kinematics During Gait Using Biplane Radiography.

Despite highly constrained motion, the sacroiliac joint (SIJ) is implicated in 15-30% of clinical low back pain syndromes. SIJ motion has been estimated in vivo by comparing two or more noncontiguous static positions. However, no literature exists to characterize dynamic in vivo SIJ kinematics during physiologic activity. This study aimed to quantify dynamic multiplanar SIJ motion in healthy individuals during gait using dynamic biplane radiography. Young, healthy participants performed treadmill walking while synchronized biplane radiographs were collected at 50 images/sec for three 1 second trials per side. CT scans of the pelvis and sacrum were used to create 3D bone models via segmentation. Digitally reconstructed radiographs were created from the 3D bone models and matched to the biplane radiographs using a volumetric tracking technique to determine six degree-of-freedom kinematics for the SIJ through the stance phase of gait. Twenty-three left- and nineteen right-sided trials in ten individuals were analyzed. The average SIJ range of motion was 2.0mm, 2.6mm, and 1.3mm in anterior-posterior, superior-inferior, and medial-lateral translation, respectively, and 2.0°, 2.0°, and 1.5° in flexion/extension, internal/external, and ab/adduction rotation, respectively. Kinematics were highly repeatable within an SIJ; the within-subject inter-trial variability was on average less than 1.3mm in translation and 0.7° in rotation. These healthy dynamic SIJ kinematics can be compared to pathologic SIJ kinematics in future studies to identify abnormalities and guide treatment strategies.