BackgroundPreoperative planning and postoperative evaluation of component position in total hip arthroplasty (THA) utilize specialized software that must be able to provide measurements that are both accurate and precise. A new software program for use in THA has recently been developed. We sought to evaluate the accuracy of this new software in comparison with two current, widely used software programs. MethodologyPostoperative anteroposterior (AP) pelvic radiographs from 135 THA patients were retrospectively reviewed. Reference values for acetabular anteversion, inclination, and leg length were established using validated software programs (TraumaCad ® as the primary reference value [PRV] and OsiriX Lite TM as the secondary reference value [SRV]). Measurements from the new software program (Intellijoint VIEW TM ) were compared with reference values using Student's t-test and chi-square test. ResultsFor anteversion, mean values for the PRV (27.34° ± 7.27°) and the new software (27.29° ± 7.21°) were not significantly different (p = 0.49). The new software differed from the PRV by a mean of 0.05° ± 0.93°. Similar results were noted for inclination, where the new software differed from the PRV and SRV by -0.13° ± 0.65°a nd 0.25° ± 1.26°, respectively (mean values: PRV: 43.62° ± 6.02°; SRV: 43.99° ± 6.27°; new software: 43.74° ± 6.17°; p = 0.87), and for leg length, where the new software differed from the PRV and SRV by 0.05 mm ± 0.46 mm and 0.22 mm ± 0.52 mm, respectively (mean values: PRV: 10.61 mm ± 11.60 mm; SRV: 10.77 mm ± 11.70 mm; new software: 10.56 mm ± 11.61 mm; p = 0.98). Measurements were highly correlated across multiple reviewers (intraclass correlation coefficient ≥0.987). ConclusionsThe new software measurement tool is accurate and precise for assessing the acetabular component position and leg length measurements following THA in AP pelvic radiographs compared to currently used image measurement software.

Background: Anteroposterior (AP) pelvic radiographs are subject to errors that may cause measurement inaccuracy in total hip arthroplasty (THA). Such errors may be detected by measuring pre- to postoperative leg-length changes in the nonoperative leg, which experiences no physical changes during THA. Methods: From AP pelvic radiographs, we measured pre- to postoperative leg-length changes (LLC) in the nonoperative legs of 67 patients who underwent primary THA using the trans-ischial line method. Results: An LLC of 0 mm was observed in the nonoperative leg in only 14 cases (21%). A LLC ⩾ 2 mm was observed in 27% (18/67) of cases, including 13% (9/67) with LLC ⩾ 3 mm and 6% (4/67) with LLC ⩾ 4 mm. A post-hoc analysis used a validated method to measure change in pelvic tilt between pre- and postoperative images and found that changes in pelvic tilt ⩾ 4° in the anterior and posterior directions created apparent lengthening (2.0 ± 1.4 mm, p  < 0.001 vs. 0–3° of tilt) and shortening (−2.1 ± 1.6 mm, p  < 0.001 vs. 0–3° of tilt) of the nonoperative leg, respectively. Conclusions: The current study provides evidence of measurement errors in leg length using AP pelvic radiographs following THA. Changes in pelvic tilt may be in part responsible for these errors, with the direction of change in pelvic tilt influencing the apparent lengthening or shortening of the lower limb. Ultimately, these findings may influence the radiographic measurement and interpretation of leg-length changes following THA.