Vibration Energy Color Doppler Imaging (VECDI) in Evaluating the Effect of Screw Fixation on Sacroiliac Joint Stiffness: A Prospective Pilot Study

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BACKGROUND: The sacroiliac joints (SIJ) are specialized articulations in the pelvis that allow load transfer between the upper and lower body. Traumatic pelvic disruption often requires surgical fixation of at least one of these joints. Subsequent SIJ pain is associated with asymmetries in joint laxity or stiffness. This pilot study examines SIJ stiffness in patients with intact sacroiliac screw fixation after posterior pelvic ring injuries. This information will prove valuable to informing surgeons about technique efficacy in SIJ injury stabilization. QUESTIONS/PURPOSES: This pilot study examined SIJ stiffness in patients with intact sacroiliac screw fixation to: (1) establish vibration energy color Doppler imaging (VECDI) SIJ intra-rater reliability; (2) measure SIJ stiffness in subjects following surgical fixation using VECDI; (3) compare stiffness data between post-surgical and healthy control subjects; (4) evaluate the relationship between stiffness data and pain and disability scores. METHODS: 13 reliability and 19 experimental subjects were tested using VECDI. Subjects were placed into a side-lying position on top of a shaker apparatus that transmitted vibration energy to the pelvic ring while color Doppler images were taken from the bilateral posterior SIJ. One investigator performed SIJ measurements on healthy subjects to establish reliability and then evaluated post SIJ fixation stiffness in experimental subjects at four-weeks (T1) and eight-weeks (T2). Visual analog scales were used to collect subjective pain scores at each time point. RESULTS: Healthy subject VECDI values suggested good intra-rater reliability (ICC = 0.819; CI 95% = 0.405-0.945). No significant differences in SIJ stiffness (ΔTU) were observed between healthy and experimental subjects at both time points (p > .05). Pearson correlation coefficients highlighted relationships between current pain at T1 and T2 (p = .004, r = .879), and Oswestry Disability Index (ODI) values at T1 and T2 (p = .003, r = .890). CONCLUSIONS: Asymmetric laxity through the SIJ can be associated with pain resulting from either trauma or inherent physiologic variations. Prior to this study, the mainstay of evaluation was subjective indexes, such as the ODI. Here we propose VECDI as a potentially objective tool in SIJ assessment. Following surgical fixation necessitated by trauma, fixation using SI screws demonstrated similar stiffness values through the SIJ at four- and eight-weeks post-operatively when compared to healthy controls. Direct inferences regarding VECDI's exact sensitivity to SIJ dysfunction cannot be concluded from our investigation due to small sample sizes. Future investigations should include a larger sample size to enhance our understanding of stiffness measurements obtained using VECDI, validate the technique, and determine the time-course of healing from SIJ surgical stabilization.

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