# Evaluation of HMDs by QFD for Augmented Reality Applications in the Maxillofacial Surgery Domain
## 2 Materials and Methods
### Desk Research on Maxillofacial Practices
#### 2.1.3. Maxillofacial Trauma Surgery  
Maxillofacial injuries are a frequent cause of emergency department visits. Traumas may present skin lacerations, burns, obstruction to the nasal cavity or sinuses, damage to the orbits, fracture to the jawbone, and missing or broken teeth. Maxillofacial trauma may also involve serious or life-threatening symptoms, such as brain injury, airway obstruction, excessive bleeding, or shock. The location of injuries may be described by the ratio 6:2:1 between mandibular, zygomatic and maxillary area [25]. The aetiology of the traumas is usually comprised between accidents (e.g., traffic, work, etc.), falls, sport activity or violence, where the ranks may vary accordingly to the considered world area. There is a rising number of maxillofacial traumas due to the rising popularity of stand-up electric scooters. Studies from Korea [26] and the US [27] highlighted how, in case of e-scooter accidents, the patients present a myriad of craniofacial trauma, ranging from abrasions, lacerations, and concussions to intracranial haemorrhage and Le Fort II and III fractures.  
In maxillofacial trauma, the patient's condition can deteriorate quickly [28], or the patient may present extended heavy injuries with tissue loss (a condition that requires a reconstruction made with bone graft). Excluding the worst cases, the most common facial traumas can be solved by reducing the fracture, placing the jaws into post-operative maxill-mandibular fixation, if necessary, and fixing the bones with a titanium mesh [29]. Many studies dedicated to maxillofacial trauma treatment show how different situations may be solved by counterintuitive solutions: it has been discovered how high-velocity maxillofacial injuries delayed treatment contributes to a critical revascularization period, resulting in improved healing and decreased post-operative morbidity and complications [30]; surgical intervention for facial trauma in elderly patients is less frequently indicated because of physiologic and psychologic changes brought on by the ageing process [31].  
Orbital injuries are common in maxillofacial traumas and a common cause of blindness. Imaging is imperative for diagnosing orbital fractures, as clinical examination can-not thoroughly assess their presence or severity [32]. The patient's CT scan images are used to extract the 3D model of the skull; then, virtual preoperatively planning is performed by a team of engineers and physicians. Once the natural head position has been defined, the normal contralateral orbit is mirrored onto the fractured orbit to define the reposition of the fractured bones and the placement of the fixing plates. The planning is then transferred to the surgical navigation system which guides the surgeon in real time through each surgical step. The surgical navigation system has two critical defects: (1) the surgeon must shift attention from the operating site to the navigation system monitor to consult the planning. The surgeon, while keeping in mind the planning information, must mentally overlap it onto the real patient while operating. This is a demanding level of concentration to maintain throughout the surgical procedure; (2) the surgical pointer, essential for the surgical navigation system position tracking, shares the access of the surgical instruments and, for this reason, the surgeon must remove it to operate. This touch-and-remove practice introduces deviations between the planning and the surgery.  
The surgeon's work could be improved and simplified using a system that shows the planning directly on the patient's face.