Personalized 3D Printed Surgical Tool for Guiding the Chisel during Hump Reduction in Rhinoplasty.

The authors aimed to present an introduction of patient-specific model in rhinoplasty by introducing a 3D printed surgical guide designed and adapted in an individualized manner for guiding dorsal hump reduction. To introduce the tool, we have designed a six step workflow. First, we obtain a digital 3D model of patient anatomy using computed tomography (CT) images. Second, we conduct a surgical preoperative planning of the rhinoplasty on the mentioned model. Third step consists of designing the guide, while taking into account nasal anthropometries and resection objectives. Fourth step is printing the guide and sterilizing it. Fifth step is performing the surgery. The last step is analyzing the main outcomes of the surgery. Our surgical guide allowed us to perform only 1 step osteotomy instead of the usual multistep osteotomy and remove exactly the amount of dorsum that we decided to remove during the preoperative planning. The duration of intervention was considerably shorter than conventional osteotomy. Using the guide was technically easier than the conventional method and reduced the learning curve from years to minutes (once the guide is printed). Moreover, the patient understanding of the procedure was significantly better after showing the 3D model of the surgery. The surgical guide allows a surgeon to transfer with extreme simplicity the presurgical planning to the surgical field. We have to point out that the design of the study does not allow us to quantify predictability, so future studies are needed to demonstrate an accuracy benefit over the former techniques.

INTRODUCTION

Since the introduction of evidence-based medicine (EBM) in medical decision making,[1] surgeons have tried to standardize procedures, approach ways and techniques to conduct the so-called “best practice,” minimize variability from 1 subject to another and maximize predictability of the outcomes.[1] Standardization of surgery has led surgeons to discard or support surgery techniques based on statistical data, so traditionally the best approach to treat a patient has been the one proven better to the majority of them.[2]

However, beyond statistical data and research evidence, there are multiple variables that influence the result and condition the eligibility of a patient for one technique or another: tissue characteristics, comorbidity, patient’s expectations, or even the familiarity of the surgeon with the technique.[3] Indeed, well understood EBM reclaims the articulation of the best available evidence with clinical expertise and patient values.[2]

As an alternative to the standardization of surgery, surgeon’s mindset is shifting from “disease-centered medicine” to “patient-centered medicine.”[4,5] The “patient-centered” approach in surgery complements EBM with comprehensive patient-specific models (PSM) that manage inter individual variability.[6]

“Rhinoplasty is a plastic surgical operation on the nose, either reconstructive, restorative, or cosmetic.” While conducting it, the surgeon has to deal with the 3-dimensional anatomy of the patient[3]; this fact adds complexity to the intervention and makes its predictability difficult.[3,7,8]

The nasal dorsum is 1 of the most important components of the nose when we look at functional and aesthetic outcomes.[9,10] For that reason, it is not surprising that the reduction of convexity of the nasal profile (also known as dorsum hump) is the most common request of rhinoplasty patients as well as 1 of the most sophisticated, dangerous, and difficult to learn.[8]

To minimize the risk, the surgeon will perform various resections until arriving at the desired amount of dorsum.[8,10] Nonetheless, this approach does not provide quantifiable predictability or millimeter accuracy.[7,10]

The aim of this article was to show that PSM is a useful tool to introduce in rhinoplasty, not only to plan the surgery, measure individual differences, and calculate the amount of hump that we want to remove but also to build personalized intraoperative instruments that aid the surgeon to deal with patient variability, increasing security and predictability of the surgery, and reducing the risk of a technical mistake.

METHODS

The authors declare that all procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. Written informed consent was obtained from all individual participants included in the study.

Products and devices used in the study: (1) All participants have had a preoperative simple spiral/helical CT scan of the head; resolution of the studies: 512 × 512 × 194; voxel size: x: 3.4133 mm, y: 3.4133 mm, and z: 1.6 mm; (2) We have conducted a surgical preoperative planning of the rhinoplasty and bone segmentation using a radiological viewer, Alma 3D; (3) Using CAD software, Rhinoceros 5, we subtracted the patient volume from the attachment part of the guide using the Boolean difference function; (4) For building our prototype, we used a Fused Deposition Modelling (FDM) printer, Witbox 2; (5) The material that we have used to print is polylactide acid (PLA), a non-toxic and biodegradable plastic widely used as surgical absorbable sutures; (6) We used CURA free software to automatically design the impression scaffold; (7) We have used the surgical guide under direct vision of an endoscope, Storz Endoscopy System, to ensure proper colocation and good behaviour during use.

The design we have chosen for this study is an experimental field trial, conducted in 2 patients (Table 1).

Table 1.

Admission Criteria

To obtain, use, and evaluate our personalized tool, we have designed a six step workflow. For guide designing, it is necessary to work on a digital patient model that gives us an accurate template of the patient anatomy; therefore, we have built our 3D digital patient model from preoperative computed tomography (CT) images. In second place, we conduct a surgical preoperative planning of the rhinoplasty using a radiological viewer (Fig. 1); this is a key step, because we have to incorporate in our design: patient desires, technical possibilities, surgeon experience, and the risk–benefit balance of being too aggressive or too conservative. Next step consists in designing the guide, taking into account structural strength, nasal anthropometric measures, and hump resection objectives; then, using computer-aided design (CAD) software, we adapt the guide attachment part to the nasal bone surface of our patient (Fig. 2). In fourth place, we print the guide using 3D rapid prototyping (see figure, Supplemental Digital Content 1, which displays a guide printed and sterilized before surgery, http://links.lww.com/PRSGO/A670). Then we perform the surgery, using the surgical guide under direct vision of an endoscope to ensure proper colocation and good behavior during use (Fig. 3; see figure, Supplemental Digital Content 2, which displays a chisel removing dorsum leaning on the guide, http://links.lww.com/PRSGO/A671). Finally, we analyze the results.

Fig. 1.

Presurgical planning.

Fig. 2.

Guide design.

Fig. 3.

Osteotomy result with guide attached.

RESULTS AND DISCUSSION

The surgical guide allows to transfer with extreme simplicity this planning to the surgical field, allowing us to remove the amount of dorsum that we decided to remove during the preoperative planning in a quick way and, more importantly, performing only 1 step osteotomy instead of the usual multistep osteotomy, leading to a safer and considerably shorter surgery (Figs. 3, 4). Also, it is remarkable that the lateral sides of the guide provide the exact point of the initial incision; therefore, it is possible to cut the cartilaginous dorsum before performing the bone fracture (see figure, Supplemental Digital Content 3, which displays a cartilaginous septum cutting (oblique view), http://links.lww.com/PRSGO/A672; see figure, Supplemental Digital Content 4, which displays a cartilaginous septum cutting (caudal view), http://links.lww.com/PRSGO/A673); those side bars, likewise, prevent the chisel from deviating and offer it an exact exit. It should be added that the placement of the guide did not require a greater detachment of the cutaneous tissue than the usual one.

Fig. 4.

Guide with dorsum fragment extracted.

This method has shown to be predictable and potentially very precise, although future studies are needed to quantify that predictability.

We have to point out that the use of the guide was technically easier, from the surgeon’s subjective valuation, than the conventional method and reduces the learning curve from years to minutes (once the guide is printed, because exhaustive formation is still needed to plan the surgery; Table 2; see figure, Supplemental Digital Content 5, which displays osteotomy using the guide under the chisel, http://links.lww.com/PRSGO/A674).

Table 2.

Surgeons Survey

Moreover, the patient understanding of the procedure was significantly better after showing the 3D model of the surgery (Table 3; see figure, Supplemental Digital Content 6, which displays a guide test using a printed model of patient nose, http://links.lww.com/PRSGO/A675).

Table 3.

Patients Survey: Patient 1 (*) // Patient 2 (^)

We used this procedure in only the first step of a very complex procedure, such as rhinoplasty, to show that this method is transferable to the operating room. But we have to point out that the aim of this study was not to quantify security, predictability, or even precision of this new technique, because we cannot compare its benefits over former ones, but we want to indicate that, as PSM is a validated approximation to inter individual differences,[3,5,6] introducing this personalized approach using our workflow in plastic surgery allows the surgeon to measure aspects that were not measurable before [like predictability or accuracy (Table 4)] and, as a result, to generate a new model based medical evidence.[6]

Table 4.

Nasal Examination: Patient 1 (Age 27) // Patient 2 (Age 61)

In the future, a greater number of patients will be necessary to consolidate our method and demonstrate its benefits over the classical technique.

ACKNOWLEDGMENTS

The authors acknowledge the moral support and advice of Dr. Felipe Macias Acuña from International University of Catalonia and the inestimable help received from Tobias Planas and Elisenda Olucha from Herrero Jover Médicos.