EP1.64 Three-Zone Planning (3Z) for Spherical Periacetabular Osteotomy: A Structured Framework for Quantitative Acetabular Reorientation
Abstract
Abstract Background Spherical periacetabular osteotomy (SPO) preserves pelvic ring continuity while enabling three-dimensional acetabular reorientation in developmental dysplasia of the hip (DDH). However, the osteotomy trajectory and fragment motion have traditionally been defined qualitatively, limiting reproducibility and hindering wider adoption. We developed a three-zone planning (3Z) concept that partitions the spherical osteotomy into superior (SZ), joint (JZ), and inferior (IZ) zones, integrated with CT-based navigation, to provide a quantitative and reproducible framework for SPO. Methods Between July 2019 and December 2024, 17 patients (18 hips) with symptomatic acetabular dysplasia underwent SPO using 3Z at a single institution. Mean age was 37 years (range, 16–59); 16 hips were female. The osteotomy trajectory was divided into SZ, JZ, and IZ on patient-specific 3D CT models, with "crossroad" contact points defined in the SZ to simulate the planned rotational arc. CT-based navigation (Stryker OrthoMap 3D) reproduced the planned cuts intraoperatively, and the acetabular fragment was fixed with bioabsorbable screws. Standardized anteroposterior radiographs were obtained preoperatively, immediately postoperatively, and at 6–12 months. Radiographic parameters included LCEA, Sharp angle, ARO, and LLD. Results Radiographic correction was achieved in all 18 hips. LCEA improved from 10.1° ± 9.0° to 31.5° ± 5.9°. Sharp angle decreased from 48.8° ± 4.0° to 40.0° ± 3.5°, and ARO improved from 19.1° ± 9.3° to 0.0° ± 5.3°. Mean structural shortening was 3.54 ± 3.74 mm; no patient reported symptomatic LLD. No deep infection, nonunion, pelvic ring fracture, or major vascular injury occurred. Transient femoral nerve palsy occurred in 5 hips, all of which resolved spontaneously. Conclusions The 3Z concept combined with CT-based navigation provides a structured and reproducible framework for SPO, enabling consistent acetabular correction while maintaining pelvic ring stability. Beyond SPO, 3Z is potentially adaptable to RAO and PAO by redefining zone boundaries, offering a common geometric platform for hip preservation surgery.