Cost-effective office 3D printing process in orthopaedics and its benefits: A case presentation and literature review

Abstract

Background and objectives

The advent of 3-Dimensional (3D) printing technology is one of the most revolutionising breakthroughs of the generation. Its benefits in surgical practice are undeniable, however a steep learning curve and concerns regarding costs may pose a barrier to large scale implementation.

Methods

We set up an in-house 3D printing facility in our institution and described our workflow. Using the described workflow, we 3D printed models which were used in the surgical management of three patients with differing conditions.

Results

We present three case examples to display the uses that 3D printing technology is able to provide in our experience, and show how 3D printing technology can be beneficial in the field of orthopaedic oncology and surgically complex cases. 3D printing has proven to be useful and improved quality of care in these case examples. The processes for each case were described individually. The benefits of our in-house 3D printing facility were discussed in detail.

Conclusion

An in-house office 3D printing facility is advantageous and cost-efficient. Its benefits can be maximised if implemented on a larger scale and has the potential to be standard of care in many institutions.

Introduction

3-Dimensional (3D) printing is one of the latest advancements in science and engineering and has gained much popularity over recent years, leading to its application in medical science. In recent years, it is gradually being integrated into routine practice in the realm of orthopaedic surgery. ¹ The incorporation of this technology into preoperative planning has shown promising improvements to surgical care of the orthopaedic patient. ² As institutions increasingly adopt 3D printing as standard of care, this paradigm shift in the preoperative planning process allows surgeons and clinicians to reap the benefits of this technology. ‘Office 3D printing’ or ‘in-house 3D printing’ refers to institutions adopting internal 3D printing programs and manufacturing 3D printed models within the institutions. The increased accessibility of 3D printing technology has made this more feasible and simple to implement. We aim to demonstrate how 3D printing technology augments preoperative planning in orthopaedic procedures in a cost-effective manner. In particular, we present case examples of the use of 3D printing for preoperative planning in orthopaedic oncology and a case of a periprosthetic fracture. We also describe our office 3D printing process workflow utilised in these cases to highlight how its cost efficiency.

Methods

A diagram summarising the 3D printing process is shown in Figure 1.

Figure 1.

Diagram summarising workflow of 3D-printing process.

Scans

In the three cases documented, Computed tomography (CT) scans of the specific area of deformity were obtained. The scans were then saved in the Digital Imaging and COMmunications (DICOM) format. The DICOM file is anonymised, so confidential patient data were not revealed.

Segmentation

The DICOM file was then converted into a 3D graphic file using a segmenting software. We used the segmenting software 3D Slicer (v4.10.2. https://www.slicer.org. Copyright 2019 Brigham and Women’s Hospital and 3D Slicer contributors). The 3D Slicer is available for download for free and we found it adequate in fulfilling and executing our 3D printing process. The segmentation process took an average of 60 minutes for each of the cases discussed in this paper.

Mesh-Mixing

We used Meshmixer (from Autodesk, California, United States) in our mesh-mixing process. Mesh-mixing involves edits made to the 3D file to customise the simulated model to the user’s preference. This includes:

- Removing unwanted segments (such as removing the portion of the scan of the fibula in cases where it does not contribute additive value to the desired final 3D model).

- Emphasising features in areas of interest in the scans to create a more detailed 3D printed model for visualisation.

- Correcting print areas that the surgeon deems are inaccurate recreations of the scan on the digital files. This can be done via the “Analysis” and then “Repair” tabs.

Slicing

The mesh-mixed 3D file requires a slicing application to convert the 3D file into a g-code, also known as STL file, which the 3D printer can print based on. We used the Cura program (Cura version 4.0, LPGLv3, Ultimaker. Website: https://ultimaker.com/software/ultimaker-cura). The Cura program also allows addition of a print support to the final model and adjustment of the orientation of the print model which maximises printing efficiency. We found the Cura program effective in our 3D printing process and also cost-saving as it is available for download for free.

Printing

The 3D printer will then print the final model based on the g-code. The equipment used in our 3D printing process include:

- 3D printer model: Creality CR-10 MAX DIY 3D Printer Kit

- Print material: Polylactic acid PLA filament

We found the equipment used in our 3D printing process to be effective in producing anatomically accurate models.

Results

We applied the 3D printing process described above on preoperative planning of several patients. We present three case examples, each with unique pathologies, whereby preoperative planning was done with the incorporation of 3D printing technology.

Cost

The cost of the 3D printing machine used was $1388 SGD. The cost of print material used was $20 SGD per kg. The cost of print material to produce each model used in the documented cases was $6 SGD (approximately 300g of print material per model).

Case 1: Excision, bone grafting and fixation of proximal tibial fibrous dysplasia

Patient is a 69-year-old male who had a benign fibrous dysplasia in his right proximal tibia. He underwent right tibia bone tumour curettage, bone grafting and internal fixation. Preoperatively, a 3D printed model was obtained. The surgeon created a cortical window on the model and performed curettage of the tumour, revealing the resultant defect to be filled. The post-curettage model was used to assess the size and dimensions of the resultant defect which guided selection of the type of bone graft for the procedure. In this case, a combination of structural bone graft (Strut graft) and cancellous bone chips were used to fill the defect. The bone defect on the model was used to prepare an appropriately-sized strut graft preoperatively. An implant plate was contoured and bent on the model. The pre-contoured plate was sent for sterilization and used in the actual surgery. A simulated fixation of the pre-contoured plate was performed on the model, during which, the position of the fibula on the 3D printed model was assessed for any potential obstruction to be anticipated. Intraoperatively, the simulated bone grafting process was replicated and performed by the surgeon in familiar anatomical territory using the bone grafts prepared preoperatively. The pre-contoured plate was accurately modelled to fit the patient’s tibia and achieved good fixation quality. Intraoperative contouring of the implant plate was not performed as a result. The procedure was carried out as planned and patient recovered well. Figure 2 shows images of the 3D-printed model used in various stages of preoperative planning of this case.

Figure 2.

Images of (a) 3D-printed anatomical model of proximal tibia with fibrous dysplasia lesion, (b) Curettage performed on lesion on model, (c) Fibular strut allograft sized and simulated on model, (d) Implant plate bent according to the contour of the model.

Case 2: Excision of osteochondroma with preoperative simulation

Patient is a 18-year-old male who presented with a swelling over his right popliteal fossa associated with discomfort when running. Plain radiographs showed a large irregular exophytic, sclerotic and dense lesion on his right posterior tibia. Magnetic resonance imaging (MRI) scans showed a pedunculated multilobulated osseous lesion with a “cauliflower appearance” which shows cortical and medullary continuity with the posterior tibia. The lesion also showed heterogenous contrast enhancement. A radiological diagnosis of a pedunculated osteochondroma arising from the proximal metaphyseal region of the tibia was made. On MRI scan, the osteochondroma was causing lateral displacement of the tibial nerve and the popliteal artery at the level of its branching. The distal popliteal artery was lying in a narrow space between the tumour and the fibular shaft, traversing extremely close to the lateral aspect of the lesion. A 1:1 scale model of the lesion and its surrounding anatomy was 3D printed. The anatomy of the lesion was visualised using the model. Due to its close proximity to the adjacent neurovascular structures, an osteotomy using a conventional medial approach was deemed risky and injury to critical structures could not be confidently prevented. An alternative approach was plotted to avoid the neurovascular structures. A trial approach and osteotomy of the lesion was performed on the 3D-printed model using computer navigation system Stryker Spinemap, simulating intraoperative conditions using the same equipment used during the procedure. Intraoperatively, the surgeon performed the excision of the posterior tibia osteochondroma replicating the same approach performed on the model, sparing the neurovascular structures traversing nearby. The bone defect was filled with HydroSet XT from Stryker. Postoperative radiographs showed complete excision of tumour and the patient recovered well. Figure 3 shows the 3D-printed model used in various stages of preoperative planning in this case.

Figure 3.

Images of (a) 3D-printed anatomical model of proximal tibia and fibula with osteochondroma lesion, (b) Stryker Spinemap navigation system used on model, (c) Intraoperative approach simulation using Stryker Spinemap navigation system, (d) Successful trial osteotomy.

Case 3: Fixation of periprosthetic tibial fracture with pre-contoured implant

Patient is a 81-year-old female who suffered a right proximal tibia periprosthetic fracture following a fall. She subsequently underwent open reduction and internal fixation using Synthes distal tibia plate and screws. Preoperatively, a 3D printed model was used to display the position of the knee replacement prosthesis in relation to the fracture site in a three-dimensional view. The extent of deformity on the model was assessed and an implant of appropriate length was selected. A simulated surgical approach was planned and performed on the model, including: planning the site of surgical incision and dissection, direction of screw placement, pre-contouring and bending of implant, and assessment of suitability of selected implant. The pre-contoured implant was subsequently sterilised and used during the actual surgery. Intraoperatively, the simulated surgical approach was replicated and performed by the surgeon using the pre-contoured implant prepared preoperatively. The pre-contoured plate was accurately modelled to fit the patient’s tibia and achieved good fracture reduction quality. Intraoperative contouring of the implant was not performed as a result. Postoperative radiographs showed the previous knee replacement prosthesis still in situ with the periprosthetic fracture fixated with the tibial plates and screws and the patient recovered well postoperatively. Function score component under the Knee Society Score ³ (KSS) was 20 at pre-procedure, 10 at 6 months post-procedure, and 60 at 2 years post-procedure. Knee score under the KSS was 41 at pre-procedure, 89 at 6 months post-procedure and 89 at 2 years post-procedure. Component scores under the Rand 36-item Health Survey ⁴ are as follows: physical function score 5 at pre-procedure, 15 at 6 months post-procedure and 30 at 2 years post-procedure; social function score 13 at pre-procedure, 25 at 6 months post-procedure and 100 at 2 years post-procedure; mental health score 24 at pre-procedure, 56 at 6 months post-procedure and 92 at 2 years post-procedure. Figure 4 shows images of the 3D-printed model used in various stages of preoperative planning in this case.

Figure 4.

Images of (a) 3D-printed anatomical model of proximal tibia depicting periprosthetic fracture, (b) Preoperative bending of implant plate against the contours of the model, (c) Intraoperative radiographs of position of implant plate.

Discussion

The integration of 3D printing technology into surgical care is increasing in popularity. A systematic review by Tack et al. ⁵ outline the advantages of this technology but also had reservations regarding its cost-effectiveness. This concern was also shared by Martelli et al. ⁶ stating that ‘The additional cost and the time needed to produce devices by current 3D technology still limit its widespread use in hospitals’. Through the documented cases above, we intend to showcase the versatility of this technology in its application in unique pathologies and how its use may be replicated in other orthopaedic conditions. Additionally, we describe our cost-effective office 3D printing process to demonstrate how this technology need not require immense costs and time. Of note, we highlight the benefits of 3D printing in the preoperative phase of orthopaedic oncology and a case of periprosthetic fracture, and how it may address current limitations in preoperative surgical planning. A review of the existing literature on 3D-printing in orthopaedic tumors and periprosthetic fractures yielded some case series and case reports. Ritacco et al., ⁷ Punyaratabandhu et al. ⁸ and Schulze et al. ⁹ documented the use of 3D printed models in the preoperative planning of orthopaedic oncological procedures. Dong et al. ¹⁰ documented outcomes of patients who underwent orthopaedic oncological procedures in a retrospective review. Han et al. ¹¹ and Marongiu et al. ¹² both documented the use of 3D printing in periprosthetic fractures. To our knowledge, there has not been a documented use of 3D-printing in the preoperative planning for a periprosthetic tibial fracture or a documented use of 3D printed model for preoperative preparation of bone grafts and the incorporation of 3D printed models in computer simulation of an orthopaedic oncological surgery.

The benefits of an office 3D printing facility in the hospital includes:

Surgeon-led printing

In our office 3D printing program, the surgeon dictates the extent and quality of printing during the mesh-mixing process. The surgeon can select portions of the scan that are required for preoperative assessment and exclude unnecessary portions (e.g., excluding the fibula in the printed model to focus on the tibia). The surgeon can also decide on the ideal orientation of the printed model to aid in preoperative assessment and maximising printing efficiency. As a result, the 3D-printing process is greatly flexible and customisable if done by the surgeon directly.

Bone graft planning

Existing literature on the use of 3D printing technology in orthopaedic oncology shows promise. A retrospective study by Park et al. ¹³ concluded that 3D printed resection guides are easy to use in orthopaedic tumor surgery. In our experience, the surgeon was able to simulate curettage of the tumour preoperatively to reveal an anatomically accurate resultant defect which was used to guide choice of type of bone graft to be used in the actual bone grafting process. This is particularly advantageous in sizable tumours causing a larger resultant defect post-curettage. The ability to pre-emptively select and prepare appropriately-sized bone grafts of suitable type improves intraoperative efficiency. Furthermore, a study by Angelini et al. ¹⁴ on the use of 3D printed prostheses for reconstruction of bone defects in bone tumours reported acceptable short term complication rates. Although not performed in our case examples, we believe that prostheses produced from 3D printing can provide alternatives and improvements the orthopaedic equipment manufacturing industry. More detailed studies with long-term outcome data are warranted to study the viability of 3D printed prostheses as alternatives to conventional bone grafts. We could be in the midst of revolutionising the production of bone grafts and prostheses.

Accurate implant placement

In deformities and altered anatomy caused by bone tumours, conventional implants might not achieve favorable outcomes. Patient-specific instrumentation (PSI) is thus imperative, especially where anatomy is unusual, as clinical outcomes are inadvertently correlated with accuracy of deformity correction.^1,15 The 3D printed models provide an anatomically accurate template on which implants can be contoured. The ability to customise mass-produced plates and implants to account for variable anatomy of deformities in different patients can allow surgeons to address the limitations of conventionally produced implants. This was observed in our experience with favourable correction outcomes achieved using the pre-contoured implants prepared preoperatively.

Compatibility and combination with other technology

The 3D printed models have various uses. Computer navigation tools such as the Stryker Spinemap is compatible with and can be used to perform image-guided navigation on the model. As the printed model is a 1:1 scale accurate representation of the patient’s anatomy, an image-guided navigation performed on the model is largely similar to navigating and exploring the real defect intraoperatively. Patients may present with challenging lesions to tackle due to proximity to surrounding structures, or anatomical aberrancy. Such cases may require personalised approaches as conventional methods may pose a higher risk of complications. In one of the cases presented, the patient had an osteochondroma that was situated in the popliteal fossa, with important neurovascular structures traversing just adjacent to it. A surgical approach to avoid critical structures was planned and performed on the model under the guidance of the same computer navigation system used intraoperatively. The accuracy of the model’s anatomy provided a near replication of the patient’s actual anatomy and its compatibility with the computer navigation system proved advantageous in familiarising the surgeon with the planned surgical approach and anatomy. Foreseeable challenges intraoperatively was anticipated and precautions could be made. A safe simulation of the procedure also allowed for adjustments for errors, thus confirming the feasibility of the planned approach. Any errors made on the 3D model can be reviewed to improve pre-operative planning, without causing potential harm to the actual patient.

Easy access

With an office 3D printing program, surgeons with the skills to utilise this technology will be able to apply it to his or her practice with great convenience. The internalization of the 3D printed model manufacturing process into the hospital infrastructure brings benefits to surgical care of patients including reduced operation duration and accurate implant placement. With easy access to this technology, office 3D printing can be adopted as standard of care and be incorporated in routine application for preoperative planning procedures.

Improved cost efficiency

The benefits of 3D printing in the preoperative planning phase has been discussed extensively in recent years with the advent of this technology.^1,16,17 A major obstacle deterring its widespread implementation is the presumed cost it incurs. A study by Ravi et al. ¹⁸ on the cost incurred in the first year of large scale implementation of 3D printing technology in an institution estimated the cost to produce an anatomical model to be greater than $2000 USD. However, a large portion of this cost was attributed to outsourcing cost. Our office 3D printing process eliminates outsourcing costs and significantly reduces production lag time. Surgeon-led printing enables a more precise mesh-mixing process in localising particular anatomy of interest. Hence, the efficiency of the print process can be maximised. With increasing accessibility of this technology and its declining costs, implementation is no longer limited to selective cases and has the potential to be standard of care. ¹⁹ As described above, the cost of print material required to print each model used in each of the cases was estimated to be around $6 SGD, which shows a vast reduction in cost compared to reported costs of outsourced 3D printing.

Improved short-term intraoperative outcomes

Reduced intraoperative duration, blood loss and use of intraoperative fluoroscopy have been observed in procedures performed which incorporated 3D printing technology in the preoperative phase in several randomised trials. A randomised prospective case-control study by Huang et al. ²⁰ comparing short term outcomes between patients undergoing surgical fixation of acetabular fractures with 3D printing technology used in preoperative planning versus conventional preoperative planning methods reported significantly shorter operation and instrumentation duration, significantly reduced blood loss and blood transfusion, and significantly reduced need for intraoperative fluoroscopy in the 3D printing group. Similar observations were reported in other randomised studies by Kong et al. ²¹ and Chen et al. ²² on distal radius fractures. Huang et al. ²⁰ also reported significantly better post-operative hip joint function (based on Harris Hip Score ²³ ) in the 3D printing group. With more extensive preoperative preparation, intraoperative duration and morbidity can be reduced. Pre-contoured plates eliminate the need for intraoperative contouring of plates and a more conducive contouring process preoperatively can produce anatomically accurate implants to achieve good fracture reduction quality. ²⁰ Simulation of surgical approaches with visualisation of relevant surrounding anatomy (such as position of existing prosthetics) also familiarises the surgeon with the procedure and allows anticipation of foreseeable challenges intraoperatively.

Protection of patient confidentiality

The DICOM files obtained from conversion of the CT scans are anonymised. Sensitive patient data are concealed, reducing risk of confidential information leak. With the whole production process internalized, it negates the need for external vendors/companies processing confidential information and averts risk of information and data leak. Ensuring safe management of patient information within the healthcare institution without the need for outsourcing production of similar models enhances protection of patient confidentiality.

Educational role

The utility of 3D printing extends far beyond the field of surgical planning and has established its role in medical education. ²⁴ Development of surgical technique and skills was previously limited to intraoperative learning and cadaveric courses. 3D printed models provide a relatively safe and cost-effective alternative. A cervical laminectomy simulation course using 3D printed models reported by Weiss et al. ²⁵ yielded promising results in discerning between proficient and novice participants. Our 3D printed models were also used in surgical training for orthopaedic trainees. The models provide three-dimensional visualisation of the anatomy and disease processes with multiple vantage points as compared to two-dimensional scans. Therefore, the application of 3D printing in orthopaedics is not limited to clinical practice but its benefits extends across other aspects of medicine, including education.

However, there are some features of 3D-printing technology that limits its application in certain clinical scenarios:

Additional preoperative preparation required

At the current stage, this technology is limited by its printing time. The printing duration to produce a model adequate for preoperative planning is significant and might not be feasible in cases requiring emergency surgery such as trauma cases where patients may deteriorate rapidly and surgeons do not have the luxury of time for a more sophisticated preoperative planning process.

Paucity of long-term data reported

Although application of 3D printing technology has been documented since the early 2000s, there is paucity of long-term outcome data on its implementation in several subspecialties in orthopaedics.^26,27 A relevant example would be the long-term feasibility of 3D printed prostheses. Current studies in the literature report on outcomes following a relatively short follow-up period. A study by Valente et al. ²⁸ on functional recovery in patients with custom-made 3D-printed anatomical pelvic prostheses following bone tumor excision had a mean follow-up duration of 32 months, while another study by Angelini et al. ¹⁴ on the use of 3D printed prostheses in reconstructive surgery for bone defects after tumor excision had a mean follow-up period of 20 months. The biocompatibility of these prostheses have not been adequately studied and reported. Further studies with long-term follow-up on the outcomes of orthopaedic procedures augmented by 3D printing technology are warranted to validate its efficacy and utility in orthopaedic surgery.

Conclusion

The emergence of 3D printing technology has been one of the greatest advancements in technology. Its versatile nature inspires its application in many fields, especially orthopaedic surgery. Its utility and improvements in perioperative surgical care have been extensively reported in existing literature. With the development of the technology and its increasing accessibility, its application and role in orthopaedics is evergrowing. This article serves to affirm its role in preoperative care through detailed description of cases where 3D printing technology was incorporated in, as well as outline our cost-effective office 3D printing process for reference. We have barely scratched the surface of harnessing the true potential of 3D printing technology and we are witnessing the dawn of a new technological advancement in this space.