SI Joint Testing

When a single clinician works longitudinally with the same patient, intra-rater reliability matters more than inter-rater reliability. SI joint motion palpation tests show intra-rater reliability ranging from 0.36 to 0.84, a spread so wide it is clinically unworkable. Ober's test with an inclinometer produces inter-rater reliability of 0.90–0.91, though this figure derives from a single study. The core liability of motion palpation tests is that clinicians tend to perceive what they expect to perceive, introducing systematic bias that degrades reliability in ways the clinician cannot detect. The substantial soft tissue between the skin surface and the SI joint raises a fundamental question about whether motion palpation meaningfully contacts the joint at all. Cadaveric evidence shows that Ober's test captures hip capsule and soft tissue mobility rather than SI joint function in isolation. A clinical test has value if it reliably tracks change and informs decisions toward the patient's goals, regardless of what structure it truly isolates.