# Computer-Aided Surgical Simulation for Correcting Complex Limb Deformities in Children
## 3 Results  
Five patients were included in the study. The patients' characteristics are described in Table 1. All procedures were successfully planned using our CASS method. The 3D printed models were successfully used during surgery, helping the surgeon to identify the correct landmarks for the osteotomy, accurately modeling and positioning hardware and bone graft when required, and, in general, giving great confidence to the surgeon during the operation. All the operations were performed by two senior surgeons, with 12 years (GT) and 25 years (GLDG) of experience in paediatric orthopaedic surgery, respectively. No complications related to the use of 3D printed models within the surgical field were reported during the operation. postoperatively, cast immobilization was maintained for 4-8 weeks in all patients but one (case 2, see complete description in Table 1), and then active rehabilitation was recommended. The surgical outcome was assessed on postoperative plain radiographs and it was considered satisfactory if the final correction, as it appeared on the postoperative plain radiographs, matched the planned correction using CASS. The surgery was precisely reproduced according to CASS and the deformities were successfully corrected in all cases but one (case 2). At the latest follow-up, three patients (case 1,3,5) achieved excellent clinical and functional results, although no postoperative outcome scores were used due to the heterogeneity of the case series. One patient (case 2) affected by focal fibrocartilaginous dysplasia [15] of the forearm, a rare deformity presenting with bowing and shortening of the forearm, loss of monosupination due to fibrocartilagineous radio-ulnar bridge, dislocation of the radial head, and negative ulnar variance, was planned for corrective surgery by CASS. The surgery, consisting of a corrective closing wedge  
Figure 3: Video animation of the second case study: (**a**) initial configuration; (**b**) removal of the bone wedge; (**c**) rotation and insertion of the bone wedge; (**d,e**) axial rotation; (**f**) final result. osteotomy of the radius, radio-ulnar bridge excision, bifocal osteotomy of the ulna, and distraction lengthening of the ulna, was performed according to CASS. However, the excised radial wedge was intentionally undersized during the operation to avoid excessive shortening of the forearm and aesthetical issues. Progressive ulnar lengthening (45 mm in 105 days) and early rehabilitation, consisting of passive and active motion of the upper limb, was started two days after surgery. Nonetheless, the insufficient shortening of the radius prevented the lever effect of the distal ulna on the corpus, and consequently, the progressive indirect relocation of the radial head. This induced an incomplete correction of the deformity, with residual negative radio-ulnar variance and persistent dislocation of the radial head. Moreover, the patient developed heterotopic bone formation along the interosseous membrane, requiring further excision. One patient (case 4) affected by genu varum in Blount disease, reported an initial excellent correction by bifocal osteotomy and bone grafting. Nonetheless, a partial relapse of the deformity was observed at the follow-up visits, therefore, a temporary hemipophysiodes of the tibia was planned during the latest visit. Two illustrative cases are reported in Figures 4-7 (case 1) and Figures 8-11 (case 3). Figure 4: A nine-year-old girl with a missed Monteggia lesion. (**a**) Antero-posterior and lateral X-ray; (**b**) CT scan with 3D reconstruction: the affected elbow showed the typical dislocation of the radial head associated with bowing of the ulna. A cap calcification is visible over the radial head. Figure 5: Simulation process: (**a**) the reconstructed 3D model is prepared for simulation through the definition of geometrical references; (**b**) the cutting plane DTM1 meets the axis A_1 defining the rotation point PNT1.