Advancements and applications of 3D printing in pediatric orthopedics: A comprehensive review

Abstract

Preoperative planning is crucial for successful surgical outcomes. 3D printing technology has revolutionized surgical planning by enabling the creation and manufacturing of patient-specific models and instruments. This review explores the applications of 3D printing in pediatric orthopedics, focusing on image acquisition, segmentation, 3D model creation, and printing techniques within specific applications, including pediatric limb deformities, pediatric orthopedic oncology, and pediatric spinal deformities. 3D printing simultaneously enhances surgical precision while reducing operative time, reduces complications, and improves patient outcomes in various pediatric orthopedic conditions. 3D printing is a transformative technology in pediatric orthopedics, offering significant advantages in preoperative planning, surgical execution, and postoperative care.

Background

Preoperative planning is paramount to achieving successful surgical outcomes and is supported by a wealth of clinical evidence. Traditionally, two-dimensional (2D) medical images are meticulously analyzed to understand the patient’s anatomical configuration and any underlying pathological conditions. This invaluable information empowers the surgeon to craft a precise surgical strategy, encompassing the choice of surgical procedure and the most effective surgical approach. The methodologies employed for preoperative planning have demonstrated advancements that have notably elevated the efficiency and precision of surgeons, as attested by notable reductions in operative duration, complications, and the length of postoperative hospital stays.^{1 –3} In the 1970s, the advent of computed tomography (CT) and magnetic resonance imaging (MRI) marked a significant milestone, swiftly establishing them as the benchmark methods for acquiring patient-specific anatomical information preceding surgical interventions. Subsequently, during the ensuing decade, the evolution of CT imaging facilitated the emergence of three-dimensional (3D) image reconstruction through volume rendering techniques. This advancement empowered surgeons with an enhanced capability to visualize and conceptualize the intricate anatomical structures of the patient.^4,5 A pivotal moment in the evolution of presurgical planning occurred in the mid-1990s with the introduction of additive manufacturing (AM) to the field of medicine. Stereolithography (SLA), the pioneering technology, marked its debut during this era. SLA utilizes 2D cross-sectional images obtained from various imaging modalities to meticulously transform them into highly precise and customized prototypes. This process culminates in the creation of a tangible 3D physical model that accurately replicates a specific anatomical structure. ⁶

Following the advent of SLA, a range of AM technologies emerged and found their way into the medical realm. Subsequently, these datasets were harnessed to construct virtual 3D models, giving birth to virtual surgical planning (VSP). This innovative tool revolutionized the exploration of surgical objectives and made its clinical debut in the early 2000s. VSP now plays a crucial role across diverse surgical disciplines, providing surgeons with invaluable insights into the intricate nuances of a patient’s anatomical configuration prior to surgical intervention.^{7 –9}

This review examines the advantageous aspects of 3D printing within the pediatric orthopedic surgical field. 3D printing has materialized as a technology with significant promise owing to its noninvasive, cost-efficiency, and user-friendly nature during surgical interventions. We also delve into the noteworthy accomplishments and potential of this technology, specifically its capacity to create tailored solutions for addressing pediatric limb deformities, in congenital scoliosis cases, and aiding in limb salvage procedures for pediatric patients with primary bone tumors. Our aim is to emphasize the transformative influence of 3D printing in pediatric orthopedics, ultimately enhancing surgical outcomes.

3D digital workflow and printing: A comprehensive review

Image acquisition and processing: CT versus MRI

Printing 3D models relies on high-quality source data from 2D imaging outputs. Commonly used 2D imaging techniques, such as CT and MRI, each provides complementary insights. CT scans are typically used to delineate osseous structures from detailed axial section images. These images are then processed using 3D software applications, resulting in highly precise models. However, this approach comes with the trade-offs of exposing the patient to ionizing radiation and reduced software performance due to large file sizes. Typically, to meet the surgeon’s requirements, slice thicknesses of approximately 1 mm are sufficient. In contrast, MRI scans typically use slice intervals that are around 4 mm. This difference arises from technical limitations that make it challenging to acquire MRI slices as thin as 1–2 mm. As MRI relies on excitation/relaxation of hydrogen molecules, extended scan times are often necessary. This can negatively affect image quality in a pediatric population because of unavoidable motion-related artifacts and disturbances. These limits may be overcome by the use of sedation, but then incur the risks thereof. While CT scans are faster and more readily available in hospitals,^10,11 MRI has a significant advantage in that it eliminates the need for patient exposure to ionizing radiation during imaging. Moreover, MRI is superior in assessing soft tissues and tumor boundaries. This is particularly evident in the case of the MRI T1 protocol, which can reveal vital details such as bone marrow condition in orthopedic bone sarcomas. In addition, this protocol can unveil insights into factors such as cartilage regularity and the extent of metastatic dissemination beyond osseous structures.^{10 –12} While CT obtains 3D volumetric imaging from which each typical plane (axial, sagittal, and coronal) can be reconstructed from a single scan, with MRI, the acquisition of the three orthogonal planes is undertaken individually. The distinct merits and drawbacks elucidated earlier establish the incapacity of either modality to function autonomously as a comprehensive imaging technique within the domain of orthopedic oncology. The 3D model is generated using CT images, augmented with soft tissue details derived from MRI scans.

Segmentation: The progression from 2D imaging to 3D virtual model

Medical images are acquired and stored in the widely adopted Digital Imaging and Communications in Medicine (DICOM) format. Boundaries of relevant tissue types are segmented on 2D slices from salient MRI or CT input and reconstructed to provide 3D information. Segmentation can be automated, semi-automated, or manual. ¹³ Segmentations obtained from the CT and MRI scans are juxtaposed and combined, a process known as fusion. Fusion entails the generation of a composite image that harmoniously integrates the insights derived from both imaging modalities allowing reconstruction of multiple tissue types. This fusion process relies on a thorough evaluation of images acquired from both imaging modalities across all three spatial dimensions (X, Y, Z). Accurate alignment of anatomical landmarks around the target bone structure is essential. Importantly, the workflow can be reversed, where image fusion precedes the segmentation of the resulting combined 2D image (Figure 1).

Figure 1.

The segmentation and registration process. (a) CT images uploaded to mimics; (b) extraction of bone tissue and separating femurs from pelvis; (c) segmentation results from MRI are in different coordinates. In yellow, bone reference of the ilium, tumor in pink, (d) parts from the MRI aligned with parts from CT.

CT, computed tomography; MRI, magnetic resonance imaging.

Transforming a 3D virtual model into a 3D printed model: The printing process

Additive engineering holds a distinct advantage over conventional subtractive manufacturing in forming objects characterized by intricate, freeform geometries. ¹⁴ Here we streamlined the procedure from patients’ medical imaging data to creating a tangible 3D model. The 2D segmentation geometries are combined into a 3D structure and exported as a Standard Tessellation Language (STL) file to computer-aided design (CAD) software. In CAD, the surgeon can then plan requisite cutting jigs or load-bearing area maps in implant cases. The virtual model is then exported as an STL file to a slicer software. Here, augmentative supports and scaffolds are appended as deemed necessary. The process culminates in the physical realization of the model through either AM method followed by post-processing. A variety of 3D medical printing technologies are employed, including VAT photopolymerization, fused deposition modeling (FDM), Powder Bed Fusion, Polyjet, and other modifications. Notably, contemporary medical 3D printing aligns with an AM framework, wherein thin cross-sectional layers of materials—comprising polymers, metals, or ceramics—are incrementally deposited and subsequently fused through light exposure, chemical reactions, or controlled temperature modulation.^15,16 Upon completion of this stage, the various layers are integrated to form a 3D model (Figure 2).

Figure 2.

Illustration of the fused deposition modeling printing process, displaying the layer-by-layer construction of a 3D model of a distal femur as simulated in GrabCAD print software by Stratasys (Eden Prairie,Minnesota.USA). In green, the model material; in orange, the support material.

The choice of 3D printing technology and materials primarily depends on the desired model characteristics, the availability of printers and materials, and practical considerations. For instance, a basic bone model can be fabricated using an FDM printer with a cost-effective polymer material. However, scenarios requiring the visualization of tumor growth within the bone necessitate the use of a Polyjet printer to create a transparent model. Furthermore, material properties must be carefully considered. Models intended for sterilization before surgical procedures may require materials that are heat-resistant or compatible with sterilization methods such as chlorhexidine treatment.

One notable advantage of AM is its heightened latitude in design complexity. This is evident in the capability to fabricate intricate geometries, wherein scaffolds or models can seamlessly integrate solid components with porous structures. This design flexibility offers pronounced versatility, especially when formulating customized implants tailored precisely to match the desired shape and location requirements. The freedom inherent in AM facilitates the realization of improved geometric adaptability, particularly in developing bespoke implants that seamlessly conform to specific anatomical contours.^17,18 Overall, AM presents a means to generate a tangible model that meticulously mirrors an individual patient’s distinct anatomical and pathological attributes. This encompasses precise alignment regarding weight, color, and even material consistency.^{19 –21}

Utilizations of 3D printing in the field of pediatric orthopedics

The 3D printing field is undergoing swift progression, encompassing diverse applications within the medical domain. These include preoperative planning, the manufacture of customized anatomical models portraying intricate pathologies such as limb deformity or tumors, the creation of sterilized patient-specific instruments (PSIs) for application during surgical procedures, and the production of implants customized to match individual patients. Of note, the realm of orthopedic surgery as a whole is at the vanguard of using 3D medical printing, commanding nearly half of all use. ²² Notably, pediatric orthopedics is at the forefront of this advancement, catalyzing innovative breakthroughs in the deployment of PSIs and personalized implants that hold the potential to enhance clinical outcomes significantly. Below, we discuss applications in printing models, PSIs, and the methodology for their use.

3D-printed anatomical models

3D modeling in pediatric orthopedics provides crucial insights into the setting of distorted anatomical features, as exemplified by tumors or bone deformities. 3D models enhance both the quality of preoperative plans developed by surgical trainees and their comprehension of the procedures. ²³ A study by Kurenov et al., focusing on implementing 3D printed models in surgical preplanning, unveiled notable benefits of reduced blood loss, decreased operative time, and shorter surgical incisions. ²⁴ Furthermore, the employment of physical 3D models empowers surgeons to anticipate the requisite instruments for executing the procedure, premised on the anatomical representation of the patient’s organ. These benefits likely result from empowering surgeons to predetermine parameters such as drill diameters and screw length, proactively shape plates as needed, plan optimal correction strategies, and emulate surgical maneuvers prior to making incisions. This capacity likely explains the reductions in operation duration, fewer complications, and enhancements in surgical outcomes that surpass the confines of a 2D model (Figure 3).

Figure 3.

Congenital scoliosis model: (a) Three hemi vertebras on T2, T6–T7 and L1–L2 without PSI; (b) same model with PSI.

PSI, patient-specific instruments.

The emergence of 3D technologies has initiated a transformative era characterized by heightened precision and tailor-made approaches to address pediatric limb deformity correction. These advancements offer a platform for intricate preoperative strategizing, encompassing facets such as gauging the extent of deformity, pinpointing optimal correction methodologies, emulating surgical maneuvers, and preemptively identifying potential obstacles—actions all orchestrated before embarking into the operating room.

3D-printed PSIs

PSIs are pivotal in pediatric surgery and progressively gaining prominence in clinical practice. They represent a prevalent class of constructs extensively utilized in surgical practice, ²⁴ assisting in both surgical preplanning and serving as intraoperative tools. PSIs empower surgeons to meticulously tailor surgical strategies, particularly in scenarios entailing intricate osteotomies linked to limb deformity corrections, interventions for congenital scoliosis, and resections involving bone tumors. While assessing entry points is commonly straightforward, evaluating the potential divergence of saws or drills within the bone proves more intricate. In this context, PSIs are indispensable tools that substantially mitigate such deviations. For instance, PSIs, such as navigational drill guides and precision cutting jigs substantially enhance the accuracy of osteotomies, particularly in complex scenarios involving multifaceted or sequential resections that demand precise cutting planes. ²⁵ Utilizing a PSI tailored to an individual’s unique bone anatomy has demonstrated improved accuracy and safety in these procedures.^{25 –27} These benefits prove particularly advantageous when PSIs are applied within intricate or delicate anatomical regions, as seen in the cases of complex limb deformities that involve the coronal, sagittal, and axial planes ²⁸ or in the pelvic region, which is characterized by complex geometries, confined operative space, and reduced intraoperative visibility, making the utilization of PSIs particularly beneficial (Figure 4).^{26,29 –32}

Figure 4.

Closing wedge osteotomy demonstrated with fused deposition modeling printed models. (a) Original femur with wedge to remove; (b) PSI fixed on the bone; (c) Femur after reduction; (d) X-ray 2 months post-surgery.

Further examples include intercalary long bone resections and distal femur resections situated near the knee joint. These scenarios involve slender margins for error in safeguarding the integrity of the knee joint following resection.^{33 –36} Another notable case involves the surgical excision of a hemivertebra in patients with congenital scoliosis. ³⁷ The same set of PSIs, produced as distinct entities, can also be applied for procuring cadaveric bone grafts after tumor resections. This standardized application of identical PSIs ensures the attainment of allografts that seamlessly match the dimensions and contour of the excised bone, a commitment to precision that remains constant throughout the process (Figure 5).

Figure 5.

PSI fixed on the bone. (a) For closing wedge osteotomy; (b) for geographic resection of tumor of distal femur.

PSI, patient-specific instruments.

Lower limb deformity corrections

Pediatric limb deformities include various conditions, spanning congenital, developmental, and acquired anomalies that disrupt the normative growth and alignment of skeletal structures during the child’s developmental stages. A wide spectrum of conditions, including leg length discrepancies, structural abnormalities, and angular or rotational deformities affecting the hips, knees, ankles, and feet, fall under the umbrella of lower limb deformities.^{38,39 –45}

Orthopedic surgeons face a substantial challenge when it comes to effectively addressing these deformities. Successful intervention requires precise planning, meticulous execution, and a thorough understanding of the intricate relationships among anatomical components. Previous reliance on conventional radiographic imaging, manual measurements, and 2D visualization was prone to error from distortion, incomplete representation of complex anatomical structures, and difficulties in sharing surgical plans between surgical team members. 3D planning mitigates several of these conventional pitfalls in limb deformity surgery. ²⁸ The integration of 3D technologies into pediatric limb deformity correction surgery has recently guided a transformative shift in treatment paradigms, leading to an era of unparalleled insights, heightened precision, and improved patient outcomes

This review outlines three primary approaches for planning and conducting limb deformity corrections based on 3D technologies.

Step 1: Preoperative planning

Mirroring method

Mirroring is a method that takes advantage of the inherent symmetry in normative anatomy and allows reconstruction via osteotomy and fixation of a deformed unilateral limb guided by a patient’s unaffected, healthy side. This approach is therefore common in trauma, infection, or bone lesions that are unilateral. It allows the surgeon to plan the necessary osteotomy and to achieve 3D deformity correction, guided by the anatomy of the unaffected and healthy contralateral bone of the same patient. In cases where the contralateral bone segment is also deformed or absent, a strategy involving a non-deformed 3D bone model from a digital repository is employed for deformity correction, a model of appropriate size is chosen and aligned with the deformed bone, serving as a reference for the mirroring technique.

Following the segmentation phase, the non-affected bone is mirrored and superimposed onto the impacted bone through CAD software. (Figure 1(a)) Using CAD software, the mirrored bone is aligned with either the proximal or distal extremity of the affected bone. The initial incision, ideally positioned at the metaphyseal region perpendicular to the bone axis and near the Center of Rotation of Angles (CORA) of the principal deformity plane, establishes the first cutting plane. Subsequent manipulation of the deformed segment, while the mirrored bone remains fixed, achieves alignment and defines the second cutting plane. These two planes collectively delineate the bone segment to be excised for a closing wedge osteotomy. This wedge encompasses the corrections required for the coronal, sagittal, and axial components of the bone deformity (Figures 6–8).

Figure 6.

The mirroring process. (a) original anatomy; (b) mirroring left femur across mid-plane; (c) wedge to remove; (d) result and mirror reference; (e) result.

Figure 7.

The resulting wedge during surgery.

Figure 8.

Preoperative AP and lateral views and 2 years post-surgery.

3D mechanical axis correction method

When normative anatomy is not present, due to bilateral deformity in the setting of congenital or metabolic pathologies, the mechanical axis method can be a helpful way of planning deformity correction. This methodology involves generating a 3D mechanical axis and utilizing the Paley method ⁴⁶ for limb deformity correction analysis. The primary objective is to precisely locate the deformed bone segment and determine the necessary correction. The anticipated postoperative mechanical axis is defined by connecting the 3D-represented center of the femoral head to the center of the tibial plateau, passing through the center of the ankle. ⁴⁷ The hinge point of the deformity is identified, and the corrective closing wedge is constructed by aligning the distorted mechanical axis (in both the coronal and sagittal planes) with the desired normal mechanical axis (Figures 9 and 10).

Figure 9.

The 3D mechanical axis process.

Figure 10.

Preoperative anteroposterior and lateral views, and 2-year postoperative follow-up.

Correction over an intramedullary nail: The virtual “Shish-Kebab” method

The adoption of intramedullary nails (IMN) for correcting deformities and achieving limb lengthening has emerged as a viable alternative to conventional methods involving external fixators and plating. IMN permit early weight-bearing and are load sharing, making them biologically favorable for bone formation. Using the “Shish-Kebab” method, we create a virtual nail (Figure 11) that precisely matches the dimensions of the medullary canal and inserts it following the standard procedure used in trauma surgery. This involves introducing the virtual nail through the greater trochanter for the proximal femur, through the center of the condyles for the distal femur, and through the proximal tibia for the tibial region. The virtual nail is then advanced in both the coronal and lateral planes. When encountering a deformity, we perform a virtual cut and correction to address the issue. The nail is then advanced further until it reaches the end of the bone or another deformity that requires correction in the coronal and lateral plane. If there is any rotational discrepancy, we can adjust it based on the patient’s physical examination or align it according to the degree of rotation in the virtual model (Figure 12).

Figure 11.

“Shish-Kebab” method. (a) original anatomy; (b) IM nail reference; (c) wedges plan; (d) first step of reduction; (e) second step of reduction; (f) final result.

Figure 12.

Preoperative AP and lateral view and 2 years post-surgery.

Step 2: Customized cutting jig design and personalized fixation devices

Following the virtual planning, post-correction bone printed model (femur or tibia) is printed and the selected virtual fixation plate is then placed in the intended location. The final model with the fixation device is scanned and segmented via CT. Then, reverse engineering is employed to execute the virtual osteotomy, restoring the bone to its initial orientation along with the screws post-corrective planning a. After validating the correction plan through conventional means, a PSI is designed. This instrument guides both osteotomy and drill hole placement based on the two cutting planes and the restored screw positions. The PSI features four integral components: Slots for accommodating the appropriate thickness saw blades, Kirschner wire (KW) sleeves to secure the tool to the bone, KW sleeves for predrilling screw holes (according to the direction of the screws), and footprint mirroring the bone’s morphology to ensure precise placement. The plate is used not only as a fixation device but also as a reduction device (Figure 13).

Figure 13.

(a) Patient’s femur at presentation; (b) the PSI; (c) PSI placed on the femur; (d) Off-the-shelf plate positioned on the femur after correction; (e) PSI during surgery; (f) Resulting osteotomies; (g) Intra-op X-ray; (h) Virtual model of a femur fixed with a bent plate; (i) CT of printed model. Where you can see spars infill of the model; (j) Segmentation of the bent plate over the printed model; (k) Screws trajectories derived from final model; (l) Screws trajectories moved back to original position.

PSI, patient-specific instruments.

Application in pediatric orthopedic oncology

Primary bone sarcomas, malignant tumors arising from bone and connective tissue, represent a significant health concern in the pediatric and adolescent population. Their global incidence is estimated to range from 10 to 26 cases per million individuals annually. ⁴⁸ Osteosarcoma, Ewing sarcoma, and Chondrosarcoma are the most prevalent types of bone sarcomas.^49,50 Osteosarcoma and Ewing sarcoma primarily affect individuals aged 5–25 years, collectively accounting for approximately 15% of all malignancies within this age group. ⁵¹ Osteosarcoma commonly originates around the knee joint, particularly in the distal femur and proximal tibia. In contrast, Ewing sarcoma typically arises within the diaphysis of long bones, with the femur, tibia, and pelvis being the most frequent sites. ⁵² These aggressive malignancies can spread through local extension, skip lesions, or hematogenous dissemination, with the lungs being the primary site of metastasis.

Primary bone sarcoma resections

Historically, amputations were the predominant approach for treating invasive bone tumors, often necessitating the removal of an extensive amount of healthy tissue to ensure complete tumor removal. ⁴⁹ Introduction of systemic chemotherapy improved oncological outcomes in these patients and together with improved implant designs enabled the surgeons to start performing limb-sparing surgery in the 1970s. This approach significantly enhanced the patient’s quality of life and mobility. ⁵⁰ However, advancements in imaging technologies have revolutionized surgical planning, ushering in an era where the utilization of custom 3D-printed implants empowers surgeons to perform highly functional limb-sparing surgeries. These procedures involve removing the tumor and affected bone while preserving as much of the surrounding limb as possible, striking a better balance between cancer eradication and maintaining functional integrity.

Despite these advancements, the diverse ways in which primary and metastatic bone tumors manifest in patients pose challenges for surgeons. The integration of 3D physical models has proven invaluable in addressing this issue. These models enhance the precision of tumor resection by providing a clearer understanding of tumor boundaries, especially in complex anatomical locations. They assist surgeons in identifying nearby structures, such as blood vessels, and nerves. By utilizing these models, surgeons gain a deeper understanding of anatomical variations and complexities, ultimately strengthening their ability to plan and execute surgical procedures with greater accuracy and effectiveness.^23,34 These advantages are particularly evident in the pelvis and knee joint.

Pelvic sarcoma resections often involve intricate 3D anatomy and proximity to critical structures (Figure 14). ⁵¹ Similarly, the distal femur and proximal tibia present unique challenges, with achieving negative margins near the knee joint often requiring knee-sacrificing surgery with an endoprosthesis. ⁵² Addressing these challenges requires innovative approaches, and the integration of 3D technology has emerged as a game-changer solution (Figure 15). Presurgical planning, combined with PSIs, enhances the precision of tumor resection by providing a comprehensive understanding of tumor boundaries and adjacent structures.^31,53 Surgical resections necessitate a meticulous approach, striving for the attainment of definite oncological boundaries. This involves the complete removal of the tumor while diligently avoiding iatrogenic injury to vital structures, which could adversely affect subsequent functional outcomes. The cornerstone of primary bone sarcoma resections hinges upon achieving negative surgical margins—excising the entirety of the neoplastic mass alongside a margin of adjacent healthy tissue. This critical aspect is paramount in preventing local recurrence and ensuring the delivery of comprehensive therapeutic intervention.

Figure 14.

An 11-year-old boy was diagnosed with Ewing’s sarcoma of the Ischium and inferior ramus pubis. The use of a PSI based on the patient’s imaging studies enabled us to perform a modified pelvic type III resection with clear margins that spared the patient’s hip joint and enabled him to return to a full and active life without a physical disability. Prior to the introduction of PSIs, we would have opted for a type II–III pelvic resection to obtain clear resection margins, which would necessitate reconstruction of the hip joint with an endoprosthesis which would result in loss of function. The X-ray shown was obtained 2 years post-surgery, the patient has no physical disability.

PSI, patient-specific instruments.

Figure 15.

Customized implant for proximal femur reconstruction; (a) X-ray at presentation of the involved leg; (b) Virtual planning of the implant; (c) The final printed implant; (d) Post-surgical X-ray of the patient’s hip joint. A 7-year-old girl presented with unresectable Osteosarcoma of the femur, with skip lesions into the femoral neck. Imaging studies showed that we could perform a soft tissue envelope sparing hip- disarticulation. Based on her pre-op CT we designed a proximal femoral implant with holes for soft tissue attachments. The final implant allowed us to leave the patient with a high-above-knee amputation. Eighteen months post-surgery she ambulates with a regular above knee prosthesis, without the help of crutches.

CT, computed tomography.

The evolution of limb-sparing surgery highlights the importance of preserving functional integrity. Techniques such as 3D technology enhance precision and facilitate joint preservation surgery, leading to better functional outcomes for patients. ⁵⁴

Lattice implants for load-bearing bone reconstruction surgery

Surgical precision in osteotomy procedures has significantly advanced with the integration of adjuvant therapies and targeted preoperative simulations, enabling precise resection margins and minimizing disease recurrence. However, limb-preserving surgeries frequently encounter the challenge of significant segmental bone loss, creating “critical-sized bone defects.” The primary objective in addressing these defects is to achieve optimal reconstruction of long bones, restoring function and minimizing the need for future surgeries (Figure 16).

Figure 16.

Customized implant for femur intercalary resection and reconstruction with post-op X-ray. A 12-year-old girl, Ewing’s sarcoma of the Femur’ underwent an intercalary resection and reconstruction with a custom-made cage and intramedullary nail. Two years post-surgery she ambulates freely and participates in sports.

Traditional approaches, such as biological bone grafts (allografts, often combined with vascularized fibular autografts), promote bone regeneration through osteoinduction, osteoconduction, and osteogenesis. However, these methods are associated with a high incidence of complications, including fractures, nonunions, delayed unions, and infections. Conversely, while conventional off-the-shelf metallic implants offer satisfactory short-term functional outcomes, they suffer from significant long-term failure rates, particularly in younger patients, due to stress shielding.

AM technology offers a promising solution, enabling the fabrication of complex, patient-specific metallic implants. These customized implants, often crafted from titanium-based alloys such as Ti-6Al-4V (Ti64) due to their favorable biomechanical properties, enhance osseointegration and minimize stress shielding effects. ⁵⁵

AM-Ti64 implants are designed to precisely fit the individual’s unique bone defect post-tumor resection, restoring function and minimizing complications. The lattice structure of the implant, reinforced with orthopedic instruments, promotes bone ingrowth and creates a transitional zone that reduces the risk of fractures at the implant-bone interface. The rapid advancement of AM technology presents a compelling alternative to traditional bone grafting approaches for weight-bearing applications in bone reconstruction (Figure 17).

Figure 17.

From top-left to right: segmentation > osteotomies > PSI > Cutout > implant > jig for guiding stem’s screws. Recurrent chondroblastoma of the Lateral Femoral Condyle (LFC) in a 13-year-old boy with severe arthritic changes after cryosurgery. A unicondylar implant was designed and implanted. The X-ray is 18 months post-surgery, the patient ambulates un-assisted without pain.

PSI, patient-specific instruments.

Application in pediatric spinal deformity

Pediatric spinal surgeons treat pathologies spanning from the occiput to the sacrum in a variety of hosts. Typical anatomy can be markedly distorted by syndromes and skeletal dysplasias,^{56 –58} congenital anomalies, or maybe markedly remodeled by Wolff’s law in advanced deformity. A thorough understanding of the deformity as well as the safe corridors avoiding neurovascular injury during screw instrumentation is therefore paramount to good planning.

Recent advances in medical imaging, especially 3D modeling and patient-specific instrumentation, have revolutionized the approach to treating complex pediatric spinal pathology. These technologies offer a safe surgical technique for young patients and enhance the understanding of both the deformity and safe corridors for instrumentation.

Use in congenital scoliosis

3D modeling significantly enhances preoperative planning for surgeries addressing congenital scoliosis. The initial step involves software segmentation of the patient’s spine CT to delineate bone from soft tissue and trace the bony anatomy. As described in the manufacturing section above, a virtual model is created to plan the surgical resection and safe corridors for screw instrumentation which can then be printed for intraoperative use (Figure 18(g) and (h)). In hemivertebra resection, the ability to visualize complex anatomy in three dimensions provides surgeons with a comprehensive understanding of the malformed vertebra and its impact on spinal curvature. The team can also design a mobile resected segment which will demonstrate the extent of the correction and the shape of the vertebral column after the correction. This aids in precise resection planning, minimizing the risk of neurologic damage to the spinal cord and nerve roots, and allowing for maximal correction of the deformity.

Figure 18.

(a) Pre-op posteroanterior view demonstrating 40° left lumbar curve with congenital right-sided L2/3 facet fusion. (b) Preoperative lateral demonstrating focal kyphosis at L2–3. (c) First erect postero-anterior view demonstrating persistent 25° left lumbar curvature and (d) first postoperative erect lateral view demonstrating correction of the focal kyphosis. The patient was subsequently managed in a nighttime bending brace (e) and (f) to modulate remaining growth and guide the spine straighter with limited fusion to L2/3. (g) Demonstrates 3D modeling for planning the correction of (h) the congenital L2/3 posterior right-sided facet fusion.

CT, computed tomography.

Likewise, 3D planning can be used in planning for interbody instrumentation for short fusion procedures, where preserving motion segments is crucial. In the provided example (Figure 18(a)–(d)) a growing 13-year-old boy had a congenital L2/3 fusion that was driving a lumbar congenital scoliosis curvature. 3D planning was used to understand the exact location of the congenital bar, plan its resection, and plan for an anterior interbody wedge to correct scoliosis without any additional loss of motion by re-arthrodesing the same levels in a more optimal position. A postoperative brace was then used to guide the growth of the remaining spinal segments to an optimal coronal and sagittal position.

There are several pediatric pathologies that can be associated with occipitocervical instability, including various skeletal dysplasias and trisomy 21.^57,59,60 Extreme care must be taken during these cases to understand the course of the vertebral artery anatomy for both exposure and instrumentation as the anatomy can be both small and anomalous relative to typical^57,60,61 leading to a notable complication rate during screw placement for both the occipital plate ⁵⁹ and tulip head screws. 3D planning has therefore been described to help plan for complex, small anatomy in these patients.^62,63 In the below example, a 10-year-old girl with trisomy 21 presented with worsening gait instability and had an imaging workup concerning atlantoaxial instability (Figure 19). She was indicated for decompression of the posterior ring of C1 and occiput to C2 fusion. 3D planning was used to determine the maximum safe lateral extent of dissection before encountering the vertebral artery at C1 and to plan the screw tracts for C2 fixation. Note that a 3.0 mm pedicle screw was planned for the left side without issue, but was felt to be difficult on the right. This therefore allowed for the planning of a bail-out option of an intralaminar screw. Because both screws could be planned with a very accurate start point and a sterilized intraoperative model, safe pedicle screws at C2 were placed bilaterally.

Figure 19.

(a) Lateral projection with colored representation from CT-angiogram of the vertebral arteries, internal jugular vein, and carotid arteries. (b) Posterior projection in the same patient with trisomy 21 and small anatomy. (c) Postoperative and preoperative lateral imaging showing the cervical spine instability and achieved screw trajectories. Patient-specific planning of screw trajectories for a left pedicle (d, f) and right pedicle (d, e) screw. Note the narrower corridor for the pedicle screw on the right side which allowed for planning for an intraoperative bail-out intralaminar C2 screw. This model was sterilized and brought to the Operating Room (OR).

CT, computed tomography.

Much has been written about the use of 3D modeling in complex spinal deformity. Karlin et al. reported on a case-controlled series of children with myelomeningocele and complex spinal deformity. Use of sterilizable 3D modeling improved operative efficiency as assessed by blood loss, fluoroscopy time, and extent of deformity correction despite the 3D modeling cohort having more complex deformity. ⁶⁴

Discussion

This review aims to establish a foundational framework for exploring the cutting-edge applications of 3D technologies in pivotal areas of pediatric orthopedic surgery, including limb deformity correction, primary bone sarcomas, and pediatric spinal deformity. By meticulously analyzing clinical data, technological advancements, and patient-reported outcomes, we seek to gain a comprehensive understanding of the potential benefits, challenges, and future directions within this burgeoning field. The integration of 3D technologies is poised to revolutionize pediatric orthopedic care, paving the way for personalized, precise, and patient-centered interventions.

The integration of 3D technologies, such as digital visualization and AM, offers innovative solutions to address several critical challenges in surgery. These include the imperative for accurate and realistic visualization, the need to standardize patient-specific surgical approaches, and the crucial requirement to enhance surgeon proficiency in a risk-free environment. Anatomical models generated through these technologies provide a profound level of visualization, offering surgeons an intuitive and comprehensive understanding of the surgical landscape. This facilitates the navigation of complex anatomical variations, empowering surgeons to adapt their approach to each unique patient. Furthermore, these models can be utilized for simulated surgical training, fostering surgeon proficiency in a safe and controlled environment, which is particularly valuable for team-based training exercises.

The emergence of PSIs is transforming the landscape of personalized surgical procedures. PSIs ensure precise anatomical alignment, enhance surgical accuracy and safety, and unlock the potential for novel patient-specific interventions. VSP, particularly when experienced through immersive technologies such as head-mounted displays, offers a distinct advantage in the preoperative phase, providing an authentic and immersive visualization experience.

The literature highlights a spectrum of complications following limb salvage surgeries, including infection, prosthesis fracture, dislocation, aseptic loosening, peripheral fractures, and neurovascular injury, with delayed bone union also presenting a significant concern.^65,66 These complications frequently culminate in surgical failure, with periprosthetic infection and aseptic loosening representing the most prevalent causes of prosthetic failure and subsequent revisions. ⁶⁷ Comparative analyses of 3D-assisted approaches versus traditional “free-hand” techniques have consistently demonstrated a significant reduction in resection lengths, complications, and postoperative morbidity.^{68 –72} Moreover, the utilization of intraoperative PSIs offers distinct advantages in determining the optimal surgical approach. In cases of long bone resections, where tumors exhibit irregular shapes and invade the surrounding bone, traditional free-hand techniques often necessitate intercalary resections, mandating a 360° cortical removal. In contrast, PSIs enable geographic resections, preserving bone continuity. This not only enhances functional and surgical outcomes but also simplifies the reconstruction process by eliminating the need to bridge separate bone segments, instead focusing on replacing the missing bone segment. Furthermore, when tumors are located in proximity to the knee or hip joints, PSIs facilitate joint-sparing surgeries, offering significant functional advantages over joint-sacrificing procedures.^{26,33 –35,68,73 –76}

To date, limb salvage surgery is the gold standard treatment for tumors surrounding the knee joint. The knee joint is usually sacrificed to maintain a safe negative margin, and a metallic modular endoprosthesis is used for joint arthroplasty and reconstruction. While this method has improved clinical outcomes compared to amputation surgery, it still has relatively high complication rates, often leading to mechanical and aseptic loosening.^{77 –79} In cases where knee joint sparing is considered, the mere few mm between the joint surface and the distal margin of the tumor creates significant challenges for surgeons when operating free hand. Although advances in imaging modalities such as MRI allow the surgeon to distinguish the exact extent of bone involvement in preoperative planning, applying this knowledge practically in the operating theater is still difficult. However, creating a 3D digital model in addition to intraoperative PSIs for accurate osteotomies can compensate for the geometric challenges of joint-sparing surgery.

Pelvic tumors often necessitate internal hemipelvectomy, a complex procedure fraught with challenges in resection and reconstruction. 3D technology significantly impacts surgical outcomes, enhancing functionality by minimizing the need for extensive reconstruction and improving the fit of allografts when reconstruction is unavoidable. Notably, 3D-planned margins afford surgeons greater flexibility in achieving free supra-acetabular margins. This transformative approach enables the conversion of previously more extensive resections (e.g., Type I–II, often requiring endoprosthetic reconstruction) into less invasive Type I resections, frequently obviating the need for any reconstruction.

Preoperative planning with 3D models for limb deformity correction enables precise multiplanar deformity correction at the apex. This facilitates a comprehensive understanding of the deformity in all three planes, including rotational malalignment. In a novel approach, not previously described in the literature, ²⁸ we printed a post-correction model. This served as a surgical template, allowing us to pre-bend the plate and simulate the planned correction. Subsequently, the model was re-scanned with the bent plate and screws in place, providing a precise surgical guide. This technique not only enhanced precision but also significantly reduced operative time. Moreover, preoperative planning on a life-size model facilitated the selection of the most suitable plate from available inventory and allowed for necessary modifications to its shape and size.

The utilization of patient-specific plates and nails in the future holds the potential to further minimize operative time and reduce the risk of complications. Our experience with this 3D multiplanar modeling approach corroborates the findings of Hu et al. ⁸⁰ regarding the significant advantages of this technique.

Limitations

While this review highlights the promising potential of 3D printing within pediatric orthopedics, it is crucial to acknowledge the inherent limitations of this emerging technology. A primary concern is the significant financial investment required for its implementation. 3D image acquisition often necessitates the utilization of multiple imaging modalities (e.g., CT and MRI), which can be costly and may not be readily available at all medical centers. Moreover, the acquisition and maintenance of specialized 3D printing equipment represents a substantial financial burden. Furthermore, the successful integration of 3D technologies necessitates the coordinated efforts of a multidisciplinary team, including medical engineers, designers, surgeons, and other healthcare professionals. A thorough cost-benefit analysis is imperative, carefully weighing these financial considerations against the potential advantages of 3D technologies, such as reduced operative time, complications, and postoperative hospitalization. While numerous studies have demonstrated improved clinical and oncological outcomes, translating these benefits into quantifiable cost-effectiveness remains an ongoing challenge. However, we anticipate that the reduction in surgical complications, comorbidities, and length of hospital stay will ultimately result in significant cost savings. Several innovative strategies are being explored to enhance the cost-effectiveness and accessibility of 3D printing technologies. These include the establishment of Point-of-Care 3D printing centers, the utilization of low-cost 3D printers, the adoption of open-source software, and the exploration of reusable materials. Concurrently, the development of robust regulatory frameworks and quality assurance guidelines is essential to ensure the safety and efficacy of 3D-printed medical devices.

Despite these current limitations, we firmly believe that the field of medical 3D printing possesses the inherent potential to overcome these challenges and ultimately establish itself as the gold standard of care within pediatric orthopedics.

Future perspective

Over the past two decades, we have witnessed remarkable advancements driven by technological innovation. 3D-printed anatomical models, intraoperative PSIs, 3D-based navigation systems, and, more recently, augmented reality (AR) technologies have all significantly improved surgical accuracy and minimized resection margins in tumor management. Fundamentally, these diverse technologies share a common origin: The transformation of basic 2D imaging data into robust 3D digital models for meticulous preoperative planning. However, their subsequent applications diverge significantly.

While 3D printing and traditional navigation systems are poised to reach a plateau in terms of innovation within the next 5–10 years, we anticipate a surge in the clinical adoption of AR technologies. This is driven by the rapid advancements in consumer AR applications and the nascent stage of its clinical implementation. In this paradigm, the 3D digital model, meticulously constructed from preoperative imaging data, transcends the physical realm. Instead of being materialized into physical objects like anatomical models or PSIs, the virtual model, complete with the integrated surgical plan, is seamlessly overlaid onto the patient in real time. This dynamic visualization guides the surgeon through the osteotomy trajectory, revolutionizing the complexity of surgical execution.

The successful translation of this vision hinges upon the development of robust and accurate intraoperative registration and navigation algorithms. By bridging this critical gap, AR technologies have the potential to redefine the landscape of pediatric orthopedic surgery, ushering in an era of unprecedented precision and personalized care.

Conclusion

A prevailing paradigm in contemporary medicine emphasizes the critical role of personalized treatment approaches. Within the realm of pediatric orthopedic surgery, 3D printing technologies have emerged as transformative tools, particularly in addressing the unique challenges posed by complex limb deformities, tumor resections, and spine deformities. The intricate and often unpredictable nature of these conditions renders traditional 2D imaging inadequate for achieving optimal surgical outcomes. 3D preoperative planning and reconstruction offer a paradigm shift, empowering surgeons to not only meticulously plan the optimal correction or resection strategy but also execute it with unparalleled precision. While these 3D-driven advancements are increasingly integrated into clinical practice, further research and refinement are necessary to establish standardized workflows for their widespread adoption in pediatric orthopedics.

The utilization of 3D-printed customized implants is a relatively recent innovation. Large-scale clinical studies are still required to define best practices and establish standardized protocols that consistently optimize patient functional outcomes and oncological outcomes. Nevertheless, a growing body of evidence strongly supports the transformative potential of these technologies to revolutionize the field of pediatric orthopedic surgery.