Observer Performance Studies

Ultrasound Evaluation of Sacroiliac Motion 
in Normal Volunteers

The goal of this study [6] was to demonstrate quantitatively, using ultrasound imaging, the passive range of motion of the normal sacroiliac (SI) joint.  Generally the SI is thought of as a joint with very little if any motion capability.  Manual medicine practitioners, however, contend that there is substantial SI motion.  This study tried to demonstrate and record SI motion.


Imaging Procedure

  • 22 volunteers without SI joint problems served as volunteers
  • Each subject had an initial rating of SI motion made using a manual medicine spring testing technique; 1 = mild mobilty; 2 = moderate mobility; 3 = sustantial mobility; 4 = very mobile
  • Manual medicine spring testing of each SI joint was performed while simultaneous ultrasound recordings were made
  • Recordings were made at the PSIS & approximately 2 cm caudal to the PSIS (inferior) levels for right & left SI joints

Image interpretation

  • The ultrasound video recordings were shown to 6 radiologists
  • On the left side of the screen was a static view of the SI level at rest
  • On the right were the real time recordings of the SI during spring testing
  • Readers were asked to judge maximum displacement (mm) of the SI during spring testing using the scale provided on the monitor
  • Readers were also asked to rate overall movement as : 0 = no motion; 1 = mild motion; 2 = moderate motion; 3 = marked motion


Percentage of cases judged to move 2 mm or more on spring testing

Joint % of Cases
PSIS AP 70.45
PSIS ML 59.85
INF AP 47.73
INF ML 51.52
PSIS AP 68.18
PSIS ML 49.24
INF AP 35.61
INF AAP 36.36

Overall Movement

  • Overall 82% of the subjects were judged to to have > 2 mm of SI movement in at least 1 joint
  • There was more movement at the AP projection than the ML projection
  • There were no male-female differences in SI movement


  • The range of passive SI joint motion is more than 2 mm and may be up to 10 mm in some subjects
  • Ultrasound is a valid technique for evaluating passive SI joint movement
  • Radiologists had little trouble identifying the relevant anatomic features necessary to make the movement judgments
  • All 6 radiologists were well correlated with each other in the judgments of motion

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