Inter-tester reliability of non-invasive technique for measurement of innominate motion

Although the complex anatomical orientation and position of the sacroiliac joints (SIJ) has rendered their 3D kinematic evaluation difficult, recent techniques of palpation-digitization of pelvic landmarks using electromagnetic tracking device have been able to accurately and non-invasively quantify the subtle SIJ kinematics. While this technique demonstrates radiographic validity and high test-retest reliability, it is yet to be assessed with regards to inter-tester and trial-to-trial reliability. A single-group repeated measure design using 4 testers was conducted to evaluate the inter-tester and trial-to-trial reliability of palpation-digitization technique for innominate vector length measurements using the Polhemus electromagnetic tracking device. Fourteen young, healthy adults between the ages of 18-40 years participated in the study. The innominate vector length was calculated from 3D co-ordinates of palpated and digitized pelvic landmarks in two test positions of hip. A sensitivity analysis was conducted to determine how palpation-digitization errors for pelvic landmarks impacts on innominate angle calculation. Reliability indexes of Intraclass correlation coefficient (ICC) (≥0.97) and Standard error of measurement (SEM) (≤2.02 mm) demonstrated very high inter-tester and trial-to-trial reliability and accuracy of palpation-digitization technique for innominate vector length measurements, irrespective of the two test positions. A higher consistency of measurements was obtained within-testers as compared to between testers, and sensitivity analysis demonstrated a negligible influence of palpation-digitization errors on the innominate angle measurements. The results support clinical and research utility of this technique for non-invasive kinematic evaluation of SIJ motion for this population. Further research on the use of this palpation-digitization technique in symptomatic population is warranted.