  This article presents a systematic review of optical see-through head mounted
display (OST-HMD) usage in augmented reality (AR) surgery applications from
2013 to 2020. Articles were categorised by: OST-HMD device, surgical
speciality, surgical application context, visualisation content, experimental
design and evaluation, accuracy and human factors of human-computer
interaction. 91 articles fulfilled all inclusion criteria. Some clear trends
emerge. The Microsoft HoloLens increasingly dominates the field, with
orthopaedic surgery being the most popular application (28.6\%). By far the
most common surgical context is surgical guidance (n=58) and segmented
preoperative models dominate visualisation (n = 40). Experiments mainly involve
phantoms (n = 43) or system setup (n = 21), with patient case studies ranking
third (n = 19), reflecting the comparative infancy of the field. Experiments
cover issues from registration to perception with very different accuracy
results. Human factors emerge as significant to OST-HMD utility. Some factors
are addressed by the systems proposed, such as attention shift away from the
surgical site and mental mapping of 2D images to 3D patient anatomy. Other
persistent human factors remain or are caused by OST-HMD solutions, including
ease of use, comfort and spatial perception issues. The significant upward
trend in published articles is clear, but such devices are not yet established
in the operating room and clinical studies showing benefit are lacking. A
focused effort addressing technical registration and perceptual factors in the
lab coupled with design that incorporates human factors considerations to solve
clear clinical problems should ensure that the significant current research
efforts will succeed.
