The effect of a non-specific gluteal contraction on transient stiffness of the sacroiliac joint as measured by Doppler Imaging of Vibrations

Abstract

The complex anatomy and kinematics of the sacroiliac joint (SIJ) has lead to much debate amongst researchers and clinicians, creating a tension between best evidence and clinical practice. A criterion standard quantifying SIJ motion does not yet exist. Doppler imaging of vibration (DIV) is one proposed method of objectively determining SIJ ‘stiffness.’ The DIV technique has shown validity and intra-session reliability, whereas inter-session reliability has thus far been observed as poor due to substandard equipment and biological variability.

Despite these limitations, research utilising the DIV technique has continued. Following the design and manufacture of a suitable vibration generator (VG), this study investigated the intra-session reliability of the new VG including control for participant generated downward pressure on the VG, and to investigate the effect of a force closure movement on SIJ stiffness as measured by DIV. Thirteen healthy participants between the ages of 19-57 years were studied. Intra-session reliability was “very high” (ICC[3,3] = 0.79; 95%CI = 0.59 to 0.90) and the standard error of measurement was calculated as 0.62 TU (95%CI = 0.50 to 0.86). A paired samples t-test showed the non-specific force closure movement had a small, nonsignificant effect on SIJ stiffness as measured by DIV (mean increase = 2.08TU; 95%CI = -1.18 to 5.34TU; P=0.20).

Participant generated downward force on the VG was observed to be constant throughout each session. Without a change in downward force, the changes in transient SIJ stiffness can more confidently be assumed to come from the force closure movement if we accept the current limitations of the DIV technique and small sample size. DIV requires further investigation into its construct validity before the results of any study employing the DIV technique are applied to any form of clinical practice.