SURGICAL-PROCEDURE SIMULATION VIA 3-DIMENSIONAL COMPUTER-AIDED RECONSTRUCTION OF DYSPLASTIC CANINE HIPS

The purpose of this study was to evaluate the use of three dimensional imaging techniques in veterinary orthopaedic surgery to measure hip c ongruity and predict changes in congruity resulting from triple pelvic osteotomies of canine hips. Preoperative, postoperative, and post-sim ulation measurements of congruity were obtained from eight canine hips by determination of Norberg angles from ventrodorsal pelvic radiograp hs (1), and lateral centre-edge (CE) angles from three dimensional (3 D) reconstructions of computed tomography (CT) scan data (2). Half of the hips were treated with a triple pelvic osteotomy with 30 degrees o f axial rotation, and the other half served as approached but unoperat ed controls. Each measurement was performed three times by a single ev aluator blinded to the identity of each hip. Lateral centre-edge angle measurements were more precise than Norberg angle measurements as det ermined by the calculated measurement of reliability (R=0.78 and 0.68 respectively). Triple pelvic osteotomy resulted in an increase in cong ruity (as measured by lateral CE angles) of 52.2 +/- 4.6 degrees compa red to -3.0 +/- 6.3 degrees in the control hips. The medical imaging p rogramme used to perform the 3D reconstructions from CT scan data also allowed manipulation of the resulting preoperative 3D images to simul ate on the computer screen the triple pelvic osteotomies performed on the gross specimens. Surgical procedure simulation predicted the chang e in congruity (as measured by lateral CE angles) of operated hips to be 43.5 +/- 8.8 degrees. The images obtained by 3D reconstruction were very sensitive indicators of gross hip morphology. Visualization of s tructures, superimposed or surrounded by bone, was easily performed on the computer by interactive manipulation of the three dimensional CT scan reconstructions. Ln addition to its unique imaging capabilities, this technique appears to be a useful method for non-invasive measurem ent and prediction of the effects of triple pelvic osteotomy on hip co ngruity in dogs.