Digital three-dimensional planning combined with 3D-printed patient-specific guide-assisted step-cut osteotomy for correction of old cubitus varus deformity: a case report.

Cubitus varus is the most common long-term complication following supracondylar humeral fractures. Although traditional step-cut osteotomy yields reliable clinical outcomes, the intraoperative osteotomy direction and angle remain largely dependent on the surgeon's experience, resulting in suboptimal precision. Although digital three-dimensional (3D) planning and 3D-printed patient-specific guides have been shown to improve osteotomy accuracy, their application in adolescent patients with long-standing cubitus varus deformity has rarely been reported. We report an 18-year-old male patient who developed progressive cubitus varus deformity 13 years after conservative treatment of a right supracondylar humeral fracture. Preoperatively, the carrying angle was -19°, with mildly restricted elbow motion and no ulnar nerve symptoms. Using mirror-image-based 3D digital planning, we designed and 3D-printed a patient-specific step-cut osteotomy guide and performed corrective osteotomy with lateral locking plate fixation. Intraoperatively, the guide was stably apposed to the bone surface, enabling precise execution of the osteotomy without displacement or interference. At 12-month follow-up, both the carrying angle and humeral-elbow-wrist angle had improved from -19° to 6.5°, elbow flexion-extension range improved from 5°-120° to 0°-135°, and the Mayo Elbow Performance Score was 95. No complications such as nonunion or nerve injury occurred, and the patient was satisfied with the surgical outcome. The combination of digital 3D planning and 3D-printed guide-assisted step-cut osteotomy may significantly enhance osteotomy accuracy and surgical safety, offering an effective approach for treating long-standing cubitus varus in adolescents. Nevertheless, given that this is a single-case report, broader studies are warranted to confirm its advantages.