The Combined Effect of Translational and Rotational Malreduction on Sacroiliac Joint Contact Surface Area

PURPOSE: Boney apposition of sacroiliac articular surfaces or anatomic reduction is of paramount importance to achieve long term stabilization through fusion of the sacroiliac joint. The amount of contact surface area in these fixated joints provides some insight into the potential fusion rates of a joint. There is a bulk of literature supporting an association between anatomic reduction and good long term outcomes, yet most of these studies define an acceptable reduction as having less than 1 cm of displacement which would be unacceptable in other areas of the skeletal system. METHODS: 14 sacroiliac joints specimens were dissected prior to scanning each face of the sacroiliac joint with a multi laser 3D scanner (NextEngine, Inc,). The 3D models were then imported into AutoCAD modeling software (Autodesk, Inc,) for manipulation. Prior to manipulation, the major and minor axes of the sacroiliac joint are defined and used as pathways for superior, posterosuperior, and posterior displacements of the sacrum on the ilium. In addition, a vertical axis as served as the center of internal and external rotation manipulations. Contact surface area for each specimen was then calculated while in the fully anatomically reduced state. This measurement was repeated as the sacrum was displaced in 2mm increments, up to maximum of 25mm, separately in all 3 translational directions. This method was repeated and contact surface area measurements recorded as the ilium was rotated internally and externally in 1 degree increments, up to maximum of 10 degrees, at each increment of translational displacement. RESULTS: Work in progress, however, all 14 specimens have been scanned with a 3D laser scanner and data collection is underway. DISCUSSION AND CONCLUSION: Current literature has only addressed planar translations of the ilia in relation to the sacrum. This is in stark contrast to the reality of typical sacroiliac disruptions which involve multiple translations in combination with internal/external rotation of the ilia. Therefore, the goal of this study was to evaluate the acceptable tolerances of malreduced sacroiliac joints through contact surface area changes in response to combined translations and rotations about the sacroiliac joint. By overcoming the limitations of prior 2 dimensional comparisons we provide a clearer picture of the necessity of anatomic reduction and the need for increased aggressiveness in the treatment of sacroiliac disruptions through our 3D study.