title: Deformation of the equine pelvis in response to in vitro 3D sacroiliac joint loading.
abstract: BACKGROUND
  Sacroiliac joint injuries can cause poor performance; however, the interaction between pelvic mechanics and the sacroiliac joint is poorly understood.
  
  
  OBJECTIVE
  To measure pelvic displacement during 3D sacroiliac joint loading.
  
  
  METHODS
  Nine reflective triads were attached rigidly to bony prominences in sacropelvic specimens harvested from 14 horses for stereophotogrammetric analysis of triad displacements and joint kinematics. The sacrum was coupled to a load cell and mounted vertically within a material testing system (MTS). A pneumatic actuator was used to apply 90 Nm moments to the ischial arch to simulate nutation-counternutation and left and right lateral bending of the sacroiliac joints. Axial rotation of the sacrum was induced by torsion of the upper MTS fixture. Vectors of marker displacement within orthogonal planes of motion were measured during loading of the sacropelvic specimens. Comparisons in the magnitude and direction of triad displacements were made between paired left-right markers and paired loading conditions.
  
  
  RESULTS
  Nutation-counternutation of the sacroiliac joint caused vertical displacement of the ischial tuberosities and cranial-caudal displacement of the wings of the ilium. Lateral bending induced rotational displacement within the horizontal plane of all pelvic landmarks, relative to the sacrum. Axial rotation of the sacrum caused elevation of the wing of the ilium ipsilateral to the direction of sacral rotation and depression of the contralateral ilial wing. Significant paired left-right differences occurred during most sacroiliac joint loading conditions. Comparable magnitudes of pelvic displacement were measured during nutation-counternutation, left and right lateral bending, and left and right axial rotation.
  
  
  CONCLUSIONS
  The equine pelvis is not a rigid structure and asymmetric pelvic deformation occurs during most sacroiliac joint movements.
  
  
  CONCLUSIONS
  Bony pelvic deformation should be considered a normal response to any sacroiliac joint movement.
authors.affiliation: Gail Holmes Equine Orthopaedic Research Center, Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA.
authors.forename: K K
authors.initials: KK
authors.lastname: Haussler
authors.forename: K C
authors.initials: KC
authors.lastname: McGilvray
authors.forename: U M
authors.initials: UM
authors.lastname: Ayturk
authors.forename: C M
authors.initials: CM
authors.lastname: Puttlitz
authors.forename: A E
authors.initials: AE
authors.lastname: Hills
authors.forename: C W
authors.initials: CW
authors.lastname: McIlwraith
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D006736:Horses / Q000033:anatomy & histology / Q000502:physiology*; D010388:Pelvis / Q000033:anatomy & histology / Q000502:physiology*