Comparison of three-versus two-dimensional pre-operative planning for total hip arthroplasty.

Background: A successful clinical outcome for total hip arthroplasty (THA) depends on accurate sizing and positioning of the implants. Using three-dimensional (3-D) pre-operative planning with a computerized tomography (CT) scan has many potential advantages over conventional 2-D planning using radiographs, including potentially more accurate assessments of the size and anteversion of the acetabulum, as well as lateral femoral offset. The purpose of this study was to compare the accuracy of 3-D to 2-D templating with respect to acetabular and femoral size, as well as lateral femoral offset. Methods: Pre-operative templating data was collected prospectively from a consecutive series of 290 primary THAs (acetabulum on all, femoral component on 255 of the cases using one specific stem). All cases were initially templated on a digital imaging picture archiving and communication (PACS) system with calibrated images to estimate the acetabular size, femoral size, and lateral femoral offset. The 3-D templating was then performed with software based on a CT scan, and the results were compared to what was surgically implanted. Results: The 3-D templating for the acetabulum was accurate 99.7% of the time based on the final implanted component. The 2-D templating for the acetabulum was accurate 39% of the time, with 46% of cases templating smaller and 15% templating larger. The 3-D templating of the femoral component was accurate 63% of the time, and within one size of final implant in 96% of cases. The 2-D templating of the femoral component was accurate 53% of the time and within one size of final implant in 94% of cases. The 2-D templated femoral offset was accurate 87% of the time and was changed in 13% of cases after 3-D templating. Conclusion: The CT-based 3-D preoperative planning was superior to 2-D planning for THA with respect to acetabular size, femoral size, and lateral femoral offset. Precise acetabular component sizing conserves bone and allows for a more predictable press fit, while facilitating efficient inventory management. Lateral femoral offset is often difficult to measure on 2-D images, and 3-D templating consistently allows for accurate offset restoration, which is important for normal hip function and stability.