A Novel Method for Correcting Pelvic Tilt on Anteroposterior Pelvic Radiographs.

Background Anteroposterior (AP) pelvic radiographs remain the standard for pre- and postoperative imaging during total hip arthroplasty (THA), despite the known limitation of plain films, including the inability to adequately account for distortion caused by variations in pelvic orientation such as pelvic tilt. The purpose of this study was to develop a reliable method for correcting pelvic tilt on AP pelvic radiographs in patients undergoing THA. Methods CT scans from 20 patients/cadaver specimens (10 male, 10 female) were used to create 3D renderings, from which synthetic radiographs of each pelvis were generated. For each pelvis, 13 synthetic radiographs were generated, showing the pelvis at between -30° and 30° of pelvic tilt, in 5° increments. On each image, eight unique parameters/distances were measured to determine the most appropriate parameters for the calculation of pelvic tilt. The most reliable and accurate of these parameters was determined via regression analysis and used to create gender-specific nomograms from which pelvic tilt measurements could be calculated. The accuracy and reliability of the nomograms and correction method were subsequently validated using both synthetic radiographs (n=50) and stereoradiographic images (n=58). Results Of the eight parameters measured, the vertical distance between the superior margin of the pubic symphysis and the transischial line (PSTI) was determined to be the most reliable (r=-0.96, ICC=0.94). Using that parameter and applying the associated nomograms to 50 synthetic radiographs of random pelvic tilt, the mean difference between the actual pelvic tilt and that calculated using the correction method was 0.1°±5.1° (p=0.98, r=0.96). In 58 stereoradiographic images, the mean difference between actual and measured pelvic tilt was -0.2°±6.4° (p=0.74, r=0.77). The pooled results indicate no significant difference between actual (2.2°±13.9°) and measured pelvic tilt (2.1°±14.3°, p=0.93, r=0.91). No significant differences were noted based on gender. Conclusions Our method of correcting for pelvic tilt using the vertical distance from the pubic symphysis to the transischial line provides a reliable method for correcting for pelvic tilt on AP pelvic radiographs.

Imageless Navigation Improves Intraoperative Monitoring of Leg Length Changes during Total Hip Arthroplasty for Legg-Calve-Perthes Disease: Two Case Reports.

Legg-Calve-Perthes disease is a rare condition characterized by avascular necrosis and malformation of the femoral head. For many patients, total hip arthroplasty (THA) is the only viable treatment option; however, there are challenges associated with THA in this population, primarily the equalization of leg lengths. Here, we present two cases of Legg-Calve-Perthes disease treated via total hip arthroplasty with the assistance of an imageless, computer-assisted navigation device. In each case, the device provided intraoperative data on leg length in real time, allowing for improved accuracy of component placement. Postoperative leg lengths were confirmed to be equalized in each case using radiographs. These cases are, to our knowledge, the first such cases using imageless navigation during THA and demonstrate the benefits of such assistive technologies in challenging cases such as Legg-Calve-Perthes disease.