Supracondylar humerus fractures are very common in children, while cubitus varus deformity may occur if these patients are not treated well (1, 2). It is considered that cubitus varus deformity belongs to a three-dimensional (3D) deformity, which includes varus deformity in the coronal plane, an overextension deformity in the sagittal plane, and an internal rotation deformity in the horizontal plane (3, 4). Lateral closing-wedge osteotomy is always performed by most orthopedic surgeons for treatment of cubitus varus deformity, which demonstrates more effective than dome osteotomy or varus osteotomy (5, 6). However, accurate performance and positioning of lateral closing-wedge osteotomy during surgery are crucial to ensure ideal correction effects.

Currently, patient specific guides for navigation, osteotomies, screw/wire positioning have been used for decades. Over the last decade, 3D printing has provided an alternative manufacturing method. Based on 3D printing technology, individualized navigation templates can completely match the solid skeleton. To make the corrective surgery more accurate in children, we need navigation templates because they have individual differences. Recently, Zhang et al. designed a computer-aided design osteotomy template for treatment of cubitus varus deformity in teenagers, which was easy to use and generated highly accurate osteotomy (7). However, the navigational template was hard to be attached to the distal humerus firmly. To solve this problem, we designed a novel 3D printing digital navigation template for treatment of cubitus varus deformity and the template was fixed hard in the bone surface. This study was aimed to evaluate whether digital navigation template was simple and precise, and could achieve accurate osteotomy degree.

For the 17 children with cubitus varus deformity in the 3D navigation template group, all templates matched well with the anatomical markers of the lateral humerus (by both intra-operative visual and post-operative imaging). Compared with the conventional group, there was statistical significance in radiation exposure (p < 0.0001) and operation time (p < 0.0001) in the 3D navigation template group (Table 2). Regarding the correcting degrees of carrying angle, there was statistical significance between the conventional group (25.1 ± 7.2°) and navigation template group (21.1 ± 5.3°, p = 0.0161).

No complications, such as incision infection, nonunion, or loss of reduction, occurred in two groups. Two cases of the prominence of the lateral condyle were found in conventional group. Radiographs showed no varus, extension, or flexion deformity at the final follow-up. In the navigation template group, 15 patients obtained excellent correction and 2 patients obtained good prognosis, while in the conventional group, 7 cases were excellent, 5 cases were good, and 3 as poor. According to the Bellemore criteria, the elbow joint function between the two groups showed no significant difference (p = 0.0288).

There are some limitations in our study. First, the number of cases was small. Second, the position of the template may be affected so we must fix the template tightly. Third, the correction of rotation should be evaluated in further studies.

Until now, closing wedge osteotomy, dome osteotomy, medial opening wedge osteotomy, step-cut osteotomy, and reverse V osteotomy have been reported (10–12). Accurately controlling the correction angle in each dimension during the lateral closing wedge osteotomy is difficult (13). 3D printing individualized navigation templates are widely used in orthopedics (14–17). Based on these technologies, 3D printing navigation templates can match the solid skeleton well (Intra-operative visual and post-operative imaging), which is safe and effective for accurate control of the angle of the osteotomy (18). Recently, different 3D printing navigation templates have been designed for cubitus varus deformity and achieved wonderful clinical outcomes (7, 19, 20). The present study applied a novel 3D printing navigation template and validated the efficacy and safety. Meanwhile, we achieved more accurate osteotomy degrees, less radiation exposure, and shorter operation time (p < 0.05). Besides, the healing time and post-operative infection were also reduced. According to the Bellemore criteria, there was significant difference between the two groups (p = 0.0288).

In the present study, the navigation template had the advantages of speed, convenience, and accuracy. It was so small that it did not expand the surgical incision, which was also simple in design and convenient during surgery. Moreover, damage of the surrounding tissues and epiphyseal cartilage were hard to be found. Third, applying the navigation template can be used to develop a preoperative plan before surgery and assist surgical navigation for accurate osteotomy. A fitting surface and upper osteotomy plane were included in the 3D printing navigation template and a Kirschner wire guide pipe was attached to the fitting surface to fix the 3D printing navigation template and avoid intraoperative slippage. After removing the template, we performed the lower osteotomy and the angle between the upper and lower osteotomy surfaces was equal to the correction of the deformity angle. Lastly, the upper and lower osteotomy surfaces were completely fitted after the osteotomy, which avoided the steps on the upper and lower osteotomy surfaces. The accuracy of the 3D printed template was checked with the aid of 3D printing model before surgery, thereby eliminating the need for repeated manipulates and shortening the surgical time. Besides, fewer radiographs are needed and continual fluoroscopic monitoring can be avoided intraoperatively.

In summary, the application of a novel 3D printing navigation template for children with cubitus varus deformity can reduce the operating time, achieve less radiation exposure and improve the surgical accuracy. Therefore, this method is effective and reliable.