Advances in Pediatric Orthopedic Surgery: 3D Calcium-Density Models for Humerus Deformity

Introduction

Fractures of the proximal humerus account for less than 5% of pediatric fractures [1]. Humerus varus is a rare condition, typically associated with neonatal fractures, occurring in children under 5 years of age. It is characterized by limb shortening and restricted shoulder motion. In advanced cases where resection of the physeal bar is not feasible, an elective valgus osteotomy is required. Correcting a malunited proximal humerus in pediatric patients through osteotomy presents a significant surgical challenge [2–4].

Proximal humerus varus is characterized by a reduction in the neck-shaft angle of the humerus, typically defined radiographically as an angle less than 140°, along with elevation of the greater tuberosity above the superior margin of the humeral neck and a decreased distance between the humeral head’s articular surface and the lateral cortex. First described by Kohler in 1935 [5], these features can be observed on anteroposterior X-rays and are commonly associated with functional limitations in shoulder motion, particularly flexion and abduction. These mechanical restrictions are often the result of subacromial impingement caused by abnormal positioning of the greater tuberosity [6]. In acquired cases, a physeal notch may also be seen medially, corresponding to localized growth arrest. Over time, this altered biomechanics can contribute to shoulder girdle weakness and compensatory overuse of the contralateral limb.

Several methods for performing valgus osteotomy have been described in the literature, including immobilization with plaster, cerclage fixation, Kirschner wires, and even rigid preformed plates [7,8]. Although 3D printing has been increasingly used for preoperative planning and surgical simulation, to the best of our knowledge, no reports have described its use for planning valgus osteotomies using models with calcium-density materials that replicate bone characteristics.

Advancements in computed tomography (CT) imaging and 3D reconstruction have enhanced the planning of upper-limb deformity corrections [9–14], leading to development of osteotomy guides for malunions of the proximal humerus [13,14]. More recently, digital printing techniques have been integrated into 3D models for planning various orthopedic corrections [15,16].

The aim of this report is to demonstrate that the planning and surgical correction of a severe proximal humerus deformity in a pediatric patient, using 3D-printed calcium-density models, was successful. This case highlights the use of advanced 3D imaging and printing technology for preoperative planning in complex orthopedic deformities. The use of 3D models facilitated accurate identification of the deformity and an optimal surgical approach, allowing precise planning of the osteotomy, correction angles, and fixation. This approach ultimately led to a successful surgical outcome, with restored mobility, pain-free function, and no complications.

Case Report

3D PLANNING:

Two key steps were undertaken before finalizing the 3D model: extraction of DICOM images and STL file generation, followed by image processing and printing. DICOM images were extracted and visualized using Horos^® open-source software. Segmentation was adjusted using Mimics^® (Materialise), and the extracted STL files were cleaned using Autodesk Meshmixer^®. The model was printed with a Lewike XL^® printer using Smartfill E.P.^® filament (Smartmaterials), composed of 70% polylactic acid and 30% calcium carbonate. This filament provides a surface finish similar to limestone and is a ceramic finish filament.

The humerus osteotomy was simulated on the 3D model using a Kirschner needle, which was passed through the most deformed region of the physeal bar and the external pivot corresponding to the center of rotation of angulation (CORA). This location was identified as the optimal site for performing the corrective osteotomy, a critical consideration in our surgical planning (Figure 5).

After simulating the osteotomy, the necessary wedge size for bone support was calculated after the model was corrected to align with the contralateral humerus. The model’s valgus and rotational deformities were adjusted, along with retroversion correction. The calculated wedge size was 15 mm (Figure 6). Temporary fixation with Kirschner wires was performed to stabilize the wedge, followed by plate fixation using the selected PediLoc® locking plate. Radioscopic imaging was used to verify screw length and positioning, facilitated by the model’s bone-like density.

SURGICAL TECHNIQUE:

The surgical intervention was performed once adequate surgical planning had been completed. A right deltopectoral approach was utilized with the patient in the supine position. During the procedure, a 3D model – previously sterilized via a 55-minute low-temperature hydrogen peroxide gas plasma process – was employed. The corrective osteotomy was carried out using the same approach previously planned on the 3D model and was executed through valgization and derotation. A 15-mm medial wedge, identical to the one in the model and harvested from the left iliac crest, was used. The osteotomy was then stabilized with 2 Kirschner wires, and deformity correction was verified using fluoroscopy. The procedure was completed by securing a PediLoc® plate (Figure 7) at the same height as indicated in the sterilized 3D-printed model prepared on the surgical table.

The size of the screws used for fixing the plate had been previously measured on the 3D model. Finally, an intra-surgical antero-posterior and lateral radioscopy was performed (Figure 8). The surgical time totaled 2 hours.

OUTCOME AND FOLLOW-UP:

The patient was maintained in a shoulder immobilizer for 10 days. An X-ray obtained afterward demonstrated a correction to a cervico-diaphyseal angle of 68°, with a postoperative angulation of 140° (Figure 9). Osteotomy consolidation was achieved 5 weeks after surgery without any complications. A significant improvement in shoulder mobility was observed, with abduction increasing from 60° to nearly 180° (Figure 10). The patient is currently pain-free and performing daily activities without any limitations.

Discussion

To the best of our knowledge, correction by osteotomy with plate fixation in skeletally immature patients was first described in 2013. Tallón-López et al reported a similar case [17] in which a proximal valgus osteotomy was performed, followed by fixation using a pre-contoured lateral malleolar plate, as pediatric-specific implants for this purpose were not available.

The use of 3D printing can be considered an additional step in the surgical protocol, offering several significant advantages. One key benefit is that 3D models provide a visual and tactile representation of underlying injuries, thereby enhancing the understanding of complex fractures or deformities. This facilitates more comprehensive preoperative planning and allows for a less invasive surgical approach. Additionally, these models enable the pre-contouring of plates to be used during surgery, ensuring their optimal fit and positioning on the bone. Another notable advantage is that surgeons can operate more efficiently and confidently, as the improved preparation reduces the need for intraoperative measurements. As a result, surgical time, blood loss, and reliance on intraoperative fluoroscopy are minimized [2–4]. Moreover, shorter surgical durations lead to reduced anesthesia time, thereby increasing patient safety. Finally, 3D models allow for clearer and more precise communication with patients regarding their condition and the planned procedure [9,13,14]. The use of this technology has contributed to advancements in the treatment of complex pathologies – for example, pelvic and acetabular fractures [18–20], as well as malignant pelvic tumors, as reported by Wang et al [21].

Recent studies showed that both surgical and radioscopy time were reduced when surgeons used 3D models. They also concluded that these models could be useful in training for surgical procedures [22]. It is sometimes very difficult to reconstruct the anatomy of the proximal humerus with X-ray and CT reconstructions of the pathological humerus. In such cases it was found useful to use the contralateral humerus for 3D reconstructions. In 2016, Vlachopoulos et al proposed the development of a computer algorithm for 3D assessment of humeral anatomy and investigating the bilateral differences of important geometric parameters in 140 patients [23].

Polylactic acid (PLA) and acrylonitrile butadiene styrene (ABS) are the most commonly used materials for printing these 3D models. Recent publications have assessed which material offers the best results. Yang et al [9] demonstrated that PLA is relatively safe, environmentally friendly, and odorless during the printing process. Unlike ABS, its main degradation product – lactic acid – is non-toxic. They also reported that PLA was associated with fewer printing failures and required shorter preparation times. Moreover, PLA offers a significant additional advantage – it can be sterilized and used intraoperatively.

In our case, we used a 3D-printed model made from Smartfill E.P., a material composed of 70% PLA and 30% calcium carbonate (CaCO3). The combination of these components in the radiopaque Smartfill E.P. filament enabled us to obtain X-ray images of the preoperatively modified printed model. This is one of its main differences compared to materials previously reported in the literature.

Bioceramics, a class of biocompatible ceramic materials, can be bioinert, bioactive, or bioresorbable and can exhibit intrinsic antibacterial properties that inhibit bacterial adhesion [24–27]. In orthopedics, biomedical engineering and 3D printing (3DP) are extensively used for patient-specific applications, including surgical models, cutting guides, and implants, thereby enhancing diagnostic accuracy, preoperative planning, and intraoperative utility while strengthening patient–provider relationships. Additionally, 3DP contributes to medical education by enabling hands-on learning about rare pathologies and facilitating understanding of complex anatomical structures without necessitating extensive radiology expertise [28–31]. Among 3DP techniques, fused filament fabrication (FFF) utilizes temperature-controlled extrusion of polymers to fabricate 3D objects, supporting multi-material printing and achieving precision through the control of critical parameters such as material viscosity, printing temperature, and polymer cooling dynamics.

The main limitation of these models, when applied to the treatment of humeral varus in children, is the lack of published cases that allow for comparison of outcomes. Additionally, a training period is required, along with time for model preparation and associated economic costs. On the other hand, we believe that in our case, the use of this radiopaque material offers significant advantages, assisting surgeons during the procedure by reducing intraoperative bleeding, fluoroscopy usage, and overall surgical time.

Conclusions

This case illustrates the successful application of 3D printing using a novel calcium carbonate-enhanced PLA material for planning and execution of proximal humerus varus correction in a pediatric patient. The 3D model facilitated improved anatomical visualization, allowed for precise pre-contouring of fixation plates, and enhanced intraoperative efficiency by reducing surgical time, bleeding, and fluoroscopy exposure. The radiopaque property of the material offered distinct advantages for radiographic assessment during both the planning phase and the surgical procedure. Although further studies are necessary to support broader clinical validation, this approach underscores the potential of 3D printing to enhance outcomes and safety in complex pediatric orthopedic surgeries.