Femoral malunion with associated sagittal and coronal deformity poses significant challenges in achieving anatomical realignment and functional restoration. This case report describes a novel surgical technique utilizing patient-specific 3D planning and a custom-designed, 3D-printed curved cutting jig to perform a dome osteotomy for deformity correction in a 69-year-old male with a history of childhood femoral fracture and recent atypical femoral fracture associated with bisphosphonate use. Preoperative CT-based 3D modeling allowed accurate assessment of the deformity and precise planning of the osteotomy. A customized jig was engineered with a hemispherical slot to guide a smooth curved osteotomy, enabling biplanar correction while preserving limb length and optimizing bony contact for healing. Intraoperative execution was streamlined by jig-guided drilling and osteotomy, followed by intramedullary nail fixation. Postoperative recovery was uneventful, with early mobilization and successful alignment and union confirmed radiographically. This approach demonstrated the value of advanced 3D technologies in enhancing surgical precision, reducing operative time and radiation exposure, and improving clinical outcomes. It represents a promising option for complex femoral deformity correction when institutional resources permit.