Deformation of the equine pelvis in response to in vitro 3D sacroiliac joint loading.
Authors: Haussler K K, McGilvray K C, Ayturk U M, Puttlitz C M, Hills A E, McIlwraith C W
Journal: Equine veterinary journal
Summary
# Editorial Summary Sacroiliac joint (SIJ) dysfunction is recognised as a significant cause of poor performance in horses, yet biomechanical understanding of how pelvic structures respond to SIJ loading has remained limited. Using stereophotogrammetric analysis of cadaveric sacropelvic specimens, Haussler and colleagues applied three-dimensional loading (nutation-counternutation, lateral bending, and axial rotation) to quantify precise patterns of bony pelvic displacement. The pelvis proved far from rigid: nutation-counternutation produced vertical movement of the ischial tuberosities and cranio-caudal displacement of the ilial wings, whilst lateral bending induced rotational displacement of all pelvic landmarks in the horizontal plane; axial sacral rotation caused elevation of the ipsilateral ilial wing with contralateral depression. Critically, asymmetric pelvic deformation occurred during most loading conditions, with significant left-right differences suggesting the pelvis responds dynamically rather than as a fixed unit. These findings reframe our understanding of normal SIJ mechanics and indicate that observed pelvic asymmetries in clinical practice may represent physiological adaptation rather than pathology—though they also highlight why asymmetrical loading (from lameness, training imbalance or poor saddle fit) could progressively stress these joints and warrant corrective intervention by the wider rehabilitation team.
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Practical Takeaways
- •Pelvic bony deformation is a normal physiological response to sacroiliac joint movement, not necessarily pathological—this should inform clinical assessment of horses with suspected SI joint problems
- •Asymmetric pelvic mechanics are expected during normal movement; look for dysfunction patterns rather than assuming symmetry is normal
- •Understanding that the pelvis deforms dynamically may help explain why some horses with SI joint issues show inconsistent performance or gait abnormalities
Key Findings
- •Nutation-counternutation of the sacroiliac joint causes vertical displacement of ischial tuberosities and cranial-caudal displacement of ilial wings
- •Lateral bending induces rotational displacement within the horizontal plane of all pelvic landmarks relative to the sacrum
- •Axial sacral rotation causes elevation of the ipsilateral ilial wing and depression of the contralateral wing
- •Significant asymmetric left-right pelvic deformation occurs during most sacroiliac joint loading conditions