Reconceptualizing Sacroiliac Joint Mechanics: From Independent Joints to a Unified Functional Unit

BACKGROUND: Pain localized to the area around the "Dimple of Venus” is a common clinical presentation in patients with low-back pain (LBP). This region represents the most peripheral dorsal portion of the sacroiliac joint (SIJ). CLINICAL QUESTION: Although the SIJ is recognized as a source of unilateral LBP, its deep anatomical location and complex morphology make diagnosis difficult. Consequently, current clinical SIJ tests often yield inconsistent results, leading to skepticism regarding the joint's clinical relevance. This doubt is largely rooted in a historically accepted biomechanical model of movement that assumes the left and right SIJs move independently. KEY RESULTS: We propose a paradigm shift in which both SIJs function as one bicondylar unit rather than two independent joints. CLINICAL APPLICATION: By recognizing reciprocal SIJ motion, our revised bicondylar model simplifies diagnosis into two distinct mechanical disorders, and could enhance the reliability, interpretation, and clinical utility of future SIJ evaluations.