Abstract
Aims
The aim of the study was to apply 3D measurements for fracture displacement in minimally to moderately displaced acetabular fractures treated nonoperatively, and to evaluate whether this measurement can be used to estimate the likelihood of conversion to total hip arthroplasty (THA) at follow-up.
Methods
A multicentre, cross-sectional study was performed on 144 patients who were treated nonoperatively for an acetabular fracture in four level 1 trauma centres between January 2000 and December 2020. For each patient, fracture displacement was measured on CT-based 3D models. The 3D gap area represents fracture displacement (mm2) between all fracture fragments. A receiver operating characteristic curve was generated to determine a 3D gap area threshold representing the optimal sensitivity and specificity to predict conversion to THA. Native hip survival was reported using Kaplan-Meier curves. Predictors of conversion to THA were determined using Cox regression analysis.
Results
Of 144 patients, 18 (12%) received a THA. The median 3D gap area of the complete study cohort was 692 mm2 (IQR 216 to 1,400). Native hip survival in patients with a gap area threshold ≤ 1,171 or > 1,171 mm2 differed at one-year (98% vs 85%), two-year (96% vs 77%), and five-year follow-up (92% vs 73%). 3D gap area > 1,171 mm2 (hazard ratio (HR) 4.3; 95% CI 1.7 to 11.0) and the presence of osteoarthritis grade 2 or higher (HR 3.1; 95% CI 1.2 to 7.8) independently predicted the likelihood of conversion to THA during follow-up.
Conclusion
For nonoperatively treated acetabular fractures, introducing 3D gap area assessment to measure fracture displacement offers a promising approach for assessing the risk of conversion to THA. With the introduction of (semi-)automatic segmentation and measurement techniques, or their implementation into commercially available software, this 3D gap area measurement can serve as an addition to the Letournel classification and an alternative to traditional 2D gap and step-off measurements, improving accuracy, reproducibility, and applicability in clinical decision-making.
Cite this article: Bone Joint J 2025;107-B(2):204–212.
