Three-dimensional navigation in maxillofacial surgery – the way to minimize surgical stress and improve accuracy in fibula free flap and Eagle’s syndrome surgical procedures

Introduction

Three-dimensional (3D) printing techniques, also known as additive manufacturing (AM), have been developing for the past three decades since 1986 [1]. However, the level of precision and accuracy required for clinical use was achieved only recently [2]. In combination with anatomically sensitive clinical imaging techniques such as MRI or CT scans, 3D printing technology in maxillofacial surgery offers important assistance in prosthetic rehabilitation, reconstruction and regeneration [3]. Low-cost 3D printing models have been used in medicine in many variations, including preoperative planning, surgical intraoperative guidance and advanced medical education [1,4]. These synthetic models improve our understanding of preoperative anatomy in individual cases, allow us to optimize our surgical approaches and introduce novel techniques tailored to a specific patent. This results in the reduction of operative time and surgical stress and minimization of perioperative errors [5,6]. In this clinical study, we present two reconstructive methods assisted by 3D printing. We were able to achieve patient-directed customized anatomical approach and identify major structural landmarks during preoperative planning. In addition, 3D printing technique enabled us to predict the stability and prepare shapes of the used alloplastic materials [3,6].

Material and methods

In this study, we used 3D printed models for navigation and planning during surgical procedures of styloid process and fibula free flap reconstruction. Printed models helped in exact location of the styloid process resection site without damaging the surrounding anatomical structures. Compared to traditional methods, in patients undergoing  mandibular resection due to malignancy, 3D models helped to identify the cutting edges and major landmarks used in mandibular reconstructive interventions.

A Form2 3D printer (Formlabs) was used to create all preoperative models. A PreForm software was used to design 3D models of temporal bone, mandible and other anatomical structures. Written informed consent was obtained from the patients undergoing surgical interventions after detailed explanation of the risks and benefits.

Results

Styloid process resection group

For the past 3 years, we identified and enrolled a total of 8 patients with 15 elongated styloid processes (Eagle’s syndrome) in this study. Seven of them underwent bilateral resection of an elongated styloid process and one patient underwent unilateral resection. Three patients had surgery without the preoperative model approach (group 1) and five patients underwent surgical procedure using the preoperative model of patient specific 3D printing of bony structures (group 2) (Fig. 1). The duration of surgery in minutes and the length of postoperative hospitalization in days were measured.

The model was examined to determine whether specific anatomical structures were located correctly and were of the appropriate shape. All 3D printed models were scanned by CT with the same parameters as those of the original temporal bone and mandible. The reproducibility of the structures such as the anatomical position, length and form of styloid process, location of the stylomastoid foramen, transversal process of the atlas and distance from the ascending ramus of the mandible were evaluated by comparing CT images of the 3D models to those of the originals. Subsequently, we used this exact 3D model preoperatively as a spatial navigation tool to perform exact resection of the styloid process.

The temporal bone and the mandible models were printed from the PLY file from biocompatible resin, in resolution of 50 microns, on a full-color FORM 2 3D printer (Formlabs Inc., Sommerville, Massachusetts, USA).

An independent t-test showed a significant difference in the operating time between group 1 (M = 148; SD = 0) and group 2 (M = 78; SD = 4.24) t (1) = 13.472; P = 0.047. There was no significant difference in the postoperative hospitalization duration (2 days), which was equal in all patient groups.

Fibula free flap reconstruction group

The 3D printed models of mandible and cutting guides for fibula resection were performed 2 weeks prior to the surgery (TruMatch, Materialise NV, Leuven, Belgium) (Fig. 2). We enrolled a total of 16 patients in this cohort. The locations of cutting lines, shape of the reconstruction, position of plate and screws was discussed in a real-time internet video conference between the manufacturer and the operating team. All patients underwent reconstruction of mandible after malignant tumor resection (1–3 segments). After dividing the patients to regular surgery (group 1–2 patients) and 3D printing assisted groups (group 2–4 patients), we assessed the same parameters as in the styloid process group – the length of surgical intervention in minutes and postoperative hospitalization duration in days. The created model was used as a guide to identify optimal cutting lines. An independent t-test revealed a significant difference in operating time in 3D printing guides group (M = 8 : 40 : 25; SD = 0 : 58 : 07) and without 3D printing guide (M = 10 : 43 : 15; SD = 3 : 04 : 32); t (14) = 2.133, P = 0.051. There was no significant difference between the groups (group 1: M = 15.5; SD = 0.71; group 2. M = 13; SD = 1.63) in the duration of postoperative hospitalization t (14) = 1.98; P = 0.119.

Discussion

Eagle’s or stylohyoid syndrome is a generally unknown and rarely identified anatomical and clinical condition. It involves the elongation of the styloid process (> 4 cm) or calcification of the stylohyoid ligament [7,8]. It is characterized by symptoms of recurrent or permanent throat and neck pain, pharyngeal foreign body sensation, dysphagia and bilateral otalgia [9,10]. The symptoms of Eagle’s syndrome are nonspecific and may mimic tumors, infection, or neuralgia what makes it quite difficult to establish the correct diagnosis based solely on clinical manifestation [11]. Eagle’s syndrome has been described as a pain syndrome associated with an elongated styloid. The congenital variant, often described as stylohyoid syndrome, has been described as a syndrome with pain and symptoms of carotid compression (syncope, presyncope, and even transient ischemic attacks) caused by an ossified stylohyoid ligament [9,12]. The incidence of abnormal stylohyoid length ranges from 4% to 28% [13,14]. The incidence is higher if calcification of the stylohyoid complex is included in 22–84% [15,16]. These symptoms can be associated with the compression of the anatomic structures that are closely related to the styloid process and the stylohyoid ligament such as facial, accessory, hypoglossal, vagal, and glossopharyngeal nerves, the internal jugular vein, and the internal carotid artery [17].

A free flap reconstruction has been a useful technique in various instances regarding maxillofacial surgery. A fibula free flap has been known to be a well-established surgical correction option in cases of mandibular reconstruction for the past 30 years [18]. This technique provides low donor-side morbidity, adequate portion of osseous graft, and a satisfactory  postoperative function leading to overall improvement of the quality of life. Virtual surgical planning (VSP) allows to perform precise osteotomies on the affected site and fit the segments of fibula in the individual prefabricated plates [19,20]. Although free flap reconstruction with fibular flap is technically feasible, yet it is still undeniably time and manpower consuming. Moreover, the postoperative period confers a risk of flap failure with added potential of a donor-side morbidity [21]. Various approaches such as 3D printing technologies are aimed at decreasing the impact of time-consuming surgical procedures on tissues and organs [6,19,22]. These techniques can be easily incorporated into specialty training curricula due to their relatively shallow learning curve. In addition, they allow for precise, anatomically correct bony reconstruction and ultimately decrease the overall surgical time [23].

Effects of surgery on tissues

Direct effects of surgery in the head and neck region are primarily related to cellular injury. In maxillofacial surgery, both direct and indirect surgical injury are present. Direct surgical injury occurs through surgical access, organ mobilization, excision, and dissection. Greater degrees of tissue injury lead to higher levels of inflammatory mediator and cytokine release, which drive immunologic, metabolic, and hormonal processes in the body known as the surgical stress response [24].

Although the development of minimally invasive surgery, robotic techniques and endoscopic interventions have greatly decreased direct tissue injury at the time, open approaches are still necessary to achieve the desired treatment goals and outcomes. Much of the direct tissue injury is caused by cervical/facial trauma or extensive scars, which may be reduced through changing incision orientation or minimizing the size of the incision [25].

Indirect injury occurs through several methods including alterations in tissue perfusion, microvascular changes associated with blood loss, and from using different anesthetic techniques. Since tissue oxygen delivery is determined by hemoglobin concentration, cardiac output, and oxygen saturation, a decrease in hemoglobin levels will directly impact the metabolic function on a cellular level. In addition, decreased oxygen delivery can lead to tissue and organ dysfunction by means of tissue hypoxemia and hypoperfusion causing the development of systemic inflammatory response syndrome and sepsis [26].

Direct surgical manipulation in the head and neck region such as retraction, ligation of vessels, removal of tissues, nerves or organ components can also negatively affect tissue perfusion. Direct injury by mechanical means causes induction of various inflammatory cascades leading to significant cellular dysfunction.

During surgical interventions, patient positioning can also pose a potential threat to the tissue microvascular environment. Prolonged unphysiological positioning, whether head up or down or various tilted positions, causes intravascular fluid shifts having deleterious effects on tissue perfusion.

Surgical stress response

Direct or indirect injuries lead to cytokine and inflammatory mediator release. In response to cellular injury, neutrophils and macrophages produce proinflammatory cytokines including tumor necrosis factor alpha (TNF-α), and several interleukins (IL-1, IL-6, IL-8) [27]. These cytokines induce the liver to increase synthesis of acute phase proteins such as C-reactive protein (CRP), albumin, ferritin, transferrin, and fibrinogen. The levels of these acute phase reactants, particularly IL-6 and CRP, correlate with the magnitude of the stress response and the development of the systemic inflammatory response [28]. Several studies have demonstrated that endoscopic and robotic surgeries are associated with lower levels of IL-6 and CRP production when compared with traditional open procedures. Patients with higher   levels of proinflammatory markers are more likely to develop postoperative complications [29]. Along with the upregulation of proinflammatory cytokines and acute phase proteins in response to surgical stress, there is also activation of the hypothalamic-pituitary-adrenal axis that leads to an elevation in counter-regulatory stress hormones including cortisol, growth hormone, glucagon, and catecholamines. One of the main surgical concerns regarding the hormonal stress response is the development of insulin resistance through the combination of catecholamine release and impaired function of the immune system [30].

Catabolic hormones and inflammatory mediators also lead to salt and water retention in response to a surgical injury. As reported in prior publications, mitochondrial activity is suppressed with an overall reduction of ATP levels. Increased inflammatory response following surgery leads to elevated production of reactive oxygen species (ROS). ROS are able to damage lipids, proteins, and even DNA, which leads to impaired vascular permeability [31]. Cell disruption from direct surgical manipulation releases several intracellular mediators including potassium, bradykinin, heat shock proteins, various cytokines/ chemokines and nerve growth factors. These have been reported to cause peripheral sensitization of nociceptors. In addition to these proinflammatory mediators, calcitonin gene-related peptide and substance P also sensitize nociceptors in adjacent tissues that were not directly injured by surgical trauma. Ultimately, this leads to central sensitization through NMDA receptors in the dorsal horn of the spinal cord and can lead to the development of hyperalgesia, allodynia, and possible chronic postsurgical orofacial pain [25].

Conclusion

Reducing operating time, decreasing the impact of surgical stress and minimizing the length of hospital stay should be the aim of every surgery. Manipulation of tissues in the head and neck region is much dependent on being familiar with the major anatomical landmarks. In case of styloid process surgery, it is crucial to avoid additional damage of the surrounding tissues (facial, accessory, hypoglossal, vagal, the internal jugular vein, and the internal carotid artery). Detailed preoperative planning by recognizing and labeling the major bone structures has shown to significantly improve the accuracy of the surgical intervention.

Our statistical analysis reveals a significant difference in measured parameters within both procedures, fibula free flap reconstructive surgery group and in the Eagle’s syndrome group, every operation with 3D navigation had a shorter absolute duration of surgery than the traditional procedure without 3D navigation model. This difference was also noted in a subset of patients who underwent reconstruction of at least three or more fibular segments in the fibula free flap group. High proficiency in identifying the individual anatomy helps to avoid errors during surgery, reduces the operative time burden and specifies the best location for safe resection of the tumor. Overall reduction of surgical time is potentially beneficial in mitigating the impact of surgical stress and leads to improved tissue healing with quicker recovery.

Roles of authors: An investigator of this study was responsible for enrolling patients in the study, following the protocol and postoperative assessment. All authors have been actively involved in the planning, preparation, analysis and interpretation of the findings, enactment and processing of the article with the same contribution

Conflict of interest: This study did not receive a specific grant from any funding agencies in the public, commercial, or not-for-profit sectors. The authors have declared no conflict of interest.

Disclosure: All procedures performed in this study involving human participants were in accordance with ethical standards of the institutional and/or national research committee and with the Helsinki declaration and its later amendments or comparable ethical standards.

Assoc. Prof. Ladislav Czakó., MD. Phd., MPH.

Department of of Oral and Maxillofacial Surgery of Medical Faculty of Comenius University  and University Hospital Bratislava

Ružinovská 6

826 06 Bratislava, Slovakia

e-mail: czako@ionline.sk

Submitted: 30.5.2021

Accepted: 23.8.2021