# Augmented Reality in Surgical Navigation: A Review of Evaluation and Validation Metrics
## 2 State of the Art AR Based Surgical Systems
### Orthopedic and Spine Surgery  
The increased interest in augmented reality in orthopedics and trauma is unsurprising considering that surgical techniques in orthopedics frequently involve visual data such as medical pictures gathered both pre- and intra-operatively. Additionally, mechanical stages such as osteectomies, screw or implant insertions, and the correction of deformities are routinely used during orthopedic surgery and can be witnessed in AR environments [50]. Spinal disorders such as degenerative ailments, deformities, trauma/spinal injuries, and spinal tumors are managed, assessed, and treated by the spine surgery. In the past ten years, minimally invasive spine surgery has made significant advancements and is now being utilized more frequently to address challenging situations [51].  
Pedicle screw implantation (a distinctly difficult procedure) in spine surgery can offer a firm fixation to the spine, preventing harm when the back extends, bends, or rotates excessively [52]. Usually, a screw that is incorrectly placed can cause neurologic and vascular problems; therefore, a navigation system is employed to assist with correct positioning [53]. During surgery, however, the surgical targets and surgical devices such as pedicle screws may be concealed in other tissues. To address these issues, research on a 3D integral videography (IV) AR system [15] for pedicle screw placement (with ultrasound-assisted registration) has been proposed [54]. Figure 5 shows a patient-specific, 3D spine model with a screw inserted at the entry point, a 2D axial image of the screw(s), and a 3D translucent image of the screw(s). To eliminate the effect of extracting anatomical markers on the surface and limit radiation exposure, ultrasound is employed to accomplish registration between the pre-operative medical imaging and the patient. Experiments show that the suggested system has adequate targeting accuracy, and that both the patient and the surgeon are exposed to less radiation.  
According to a 12-question survey conducted globally in [16], spine physicians recognise the usefulness of computer assisted surgery, but current technologies fall short of their expectations in terms of usability and integration into the surgical work flow. Speed, accuracy, and urgency are the key in spine or orthopedic treatments. For instance, the majority of orthopedic or spinal surgeries require anesthesia before the surgery because of the severity of pain and other procedural requirements. Thus, before the effect of anesthesia is over, the procedure has to be finished. The post Deep Venous Thrombosis (DVT) stage is so acute that the patient needs urgent attention. Thus, the computer assisted models should be affordable in terms of user friendliness, computationally inexpensive, and fast so that they can be used frequently. Even after reaching the state, where supercomputer is available (although not available abundantly), appropriate visualization still remains a problem, which the clinicians rank the most among others. Thus, in orthopedic and spine surgery, augmented reality has the potential and capability to save time, reduce radiation and risk, and improve precision.  
Figure 5: (a) Screw insertion on 3D, patient-specific spine model; (b) 2D axial image of placed pedical screws; and (c) 3D translucent image of implanted screws [52].