Measurement of sacroiliac joint stiffness with Doppler imaging of vibrations – A reliability study

Abstract

Introduction: Sacroiliac joint (SIJ) motion dysfunction and its role in low back and pelvic pain remains an unresolved issue amongst the medical fraternity. Clinical objective SIJ motion and pain detection methods are both expensive and difficult to reproduce whilst most manual methods of SIJ motion assessment have been contentious with regard to their reliability. Doppler Imaging of Vibrations (DIV) has been advocated as one alternative adjunct method of evaluating SIJ dysfunction.

Purpose: The aim of this research was to test reliability of the DIV technique to assess SIJ stiffness within a normal population when using a custom built Vibration Generator (VG).

Methodology: Thirteen healthy participants with an age range of 23-50 years, 4 females (mean age 27 ± 5 years, height 167 ± 13cm, weight 65 ± 11 Kg) and 9 males (mean age 33 ± 9 years, height 176 ± 5cm, weight 76 ± 8 Kg) were assessed for SIJ stiffness using the DIV technique over two sessions. Participants were positioned in prone and vibration applied unilaterally to the anterior superior iliac spine. Vibrations were registered by a Colour Doppler Imaging (CDI) transducer over the ipsilateral SIJ. A Threshold Unit (TU) is the difference between ipsilateral sacral and ilial threshold level (TL) values and was accepted as the measured loss of vibrational power across the SIJ. A large difference between bilateral SIJ TU values in individuals is assumed to be indicative of SIJ stiffness asymmetry. Interclass correlation coefficients (ICC) with 95% confidence intervals (CI) were used to calculate intra and inter-session reliability. Standard error of the measurement (SEM) calculations were undertaken to assess difference between the actual measured score across trials and the smallest detectable difference (SDD) was calculated from the SEM to indicate the degree of change that would exceed the expected trial to trial variability.

Results: All intra-session ICC reliability scores for DIV testing of SIJ stiffness were ’excellent’ with ‘substantial’ to ‘almost perfect’ CIs. Inter-session ICC reliability scores for DIV testing of SIJ stiffness were ‘excellent’ with ‘moderate’ to ‘almost perfect agreement’ CIs for S1 means against only less than ‘acceptable’ to ‘acceptable’ ICC scores with ‘poor’ to ‘fair agreement’ CIs for S2 means. Only three participants were observed to have a consistent SIJ stiffness pattern over all intra-session measurements.

Conclusion: The DIV technique, when performed using a custom built VG to detect SIJ stiffness asymmetry in a normal population, showed a satisfactory level of intra-session reliability but a lower than satisfactory level of inter-session reliability. Further technical modifications are required to ensure the VG maintains robustness and signal consistency for future studies.