P134 - Weight Bearing 3D Models of the Lower Limbs
- K. Verdonschot (Utrecht, NL)
- K. Verdonschot (Utrecht, NL)
- H. Nguyen (Utrecht, NL)
- A. Zeydi (Utrecht, NL)
- R. Custers (Utrecht, NL)
- N. Van Egmond (Leusden, NL)
- H. Weinans (Utrecht, NL)
- V. Arbabi (Utrecht, NL)
Abstract
Purpose
The gold standard for preoperative osteotomy planning of the lower limbs requires weight-bearing whole leg radiographs (WLR). However, sagittal and transversal deformities can be overlooked on these 2D images. Additional 3D CT scans can provide this information but lack the weight-bearing aspect. The combination of 3D information with weight-bearing is especially useful in the care of patients presenting knee osteoarthritis with deformities in multiple planes. The aim of this research is to investigate the possibility of creating a weight-bearing 3D model of the lower limbs from a CT scan and a single WLR of the patient (Figure 1).
Methods and Materials
Software was developed for manually aligning 3D models onto a single anteroposterior weight-bearing WLR. This study included 30 patients with available CT scans. Digitally reconstructed (whole leg) radiographs (DRR) and anatomical 3D models were computed from these CT scans. Three raters performed manual registrations of the anatomical 3D models onto the DRRs using the software. The registered 3D models were compared to the 3D models in their original state. Errors were expressed in absolute distances and errors measured in the lower limb geometry: frontal hip knee angle (HKA), sagittal HKA, joint line convergence angle (JLCA), and tibio-femoral rotation.
Results
Mean registration error was highest in the sagittal plane (6.10mm SD ± 4.47mm) compared to the anteroposterior plane (0.89mm SD ± 0.39mm). The angular error was highest for the sagittal HKA and tibio-femoral rotation, respectively 1.63° SD ± 1.28° and 1.69° SD ± 1.33°, and lowest for frontal HKA and the joint line conversion angle, respectively 0.60° SD ± 0.60° and 0.54° SD ± 0.64° (Figure 2).
Conclusion
Manual registration of 3D models onto 2D DRRs provide accurate results in the antero-posterior plane, but results are less accurate in the sagittal plane. This resulted in reliable 3D weight-bearing lower limb models in the frontal plane.