Holographic Augmented Reality for DIEP Flap Harvest

I read with great interest the article by Wesselius et al.1 on the possible application of augmented reality for deep inferior epigastric perforator (DIEP) flap harvest. Although this technology, without a doubt, has a bright future, it still has several limitations in the surgery that I feel were not mentioned by the authors. Therefore, based on my own experience with augmented reality in reconstructive surgery, I would like to draw readers’ attention to some essential matters. The authors’ method utilizes the same workflow as a typical intraoperative navigation system: image data acquisition, patient registration, and tracking.1 The only difference is the method of presenting data, in this case, via augmented reality display instead of a monitor screen. Although it seems spectacular, the real matter is how accurate and reliable it is in the clinical setting. Several studies tested the use of intraoperative navigation for the DIEP flap harvest.2–4 Yet, this support method was not incorporated into practice. In my opinion, the augmented reality guidance for DIEP shares the same drawbacks as its predecessor, which limits its clinical usefulness. First, displayed virtual anatomy, based on a computed tomography image captured in a specific moment, is static. It is not updated as tissue alteration occurs during the surgery. In other words, the virtual plan or anatomy is reliable up to the moment of the first incision. Then tissue shifts occur, and virtual data are outdated. As surgery continues, the anatomical data imposition becomes more misleading. Besides, one must also consider such disturbing factors as breathing and muscle relaxation during general anesthesia.2,3 Those also create constant soft tissue shifts that current intraoperative navigation cannot track. That is why this technology, regardless of the data display method, found real clinical application only in neurosurgery and maxillofacial and spinal surgery.3 Bones and enclosed brain tissue are less prone to movement; therefore, it is possible to retain navigation accuracy, even to the surgery’s very late steps. Second, the navigation accuracy depends on the registration process. Although the point-pair technique used in the study is considered the most accurate method of the virtual image imposition on the patient’s body, the authors did not present its accuracy (target registration error parameter). Registration is difficult to conduct on the abdomen.2–4 Landmarks on the skin are prone to movement due to breathing and muscle relaxation compared with their location on the computed tomography image. It is believed that landmarks on fixed skin, such as the scalp or limb regions, offer reliable registration. When one analyzes the abovementioned factors, the following question arises. If augmented reality technology cannot offer reliable and accurate navigation during the surgery, how is it better than perforator vessel marking using ultrasonography? The potential applications of augmented reality technology should be very carefully interpreted. In my opinion, at its current level of development, it offers support mainly in the craniomaxillofacial region. Other realistic applications include supporting the harvest of the fibula and iliac bone flaps.5 It also seems reasonable as an aid in elevating perforator flaps of the limbs in the regions with fixed skin and a thin subcutaneous tissue layer.