Robot‐assisted scaffold implantation and two‐stage flap raising of the greater omentum for reconstruction of the facial skeleton: Description of a novel technique

Bone regeneration in the greater omentum is a promising strategy in facial skeleton reconstruction. This feasibility‐study aims to perform robot‐assisted scaffold implantation and second‐stage flap raising.


| INTRODUCTION
The standard of care in facial skeleton reconstruction after ablative oncological treatment or jaw bone osteonecrosis secondary to radiation, antiresorptive medication or severe infection is the use of autologous microvascular bone grafts from the fibula, scapula or iliac crest. 1 Autogenous bone harvesting is associated with a risk of donor site morbidity like instability and deformity, muscle weakness and functional limitations. 2 Moreover, as the facial skeleton presents a complex three-dimensional anatomy, the shape and extend of bone grafts are insufficient in many cases. 3 In recent decades, many approaches to bone cultivation and ectopic endocultivation of bone flaps have been developed as an alternative approach -also to reduce the morbidity of existing therapies. [4][5][6] The reconstruction by endocultivation using 3dimensional (3D)-printed scaffolds in the greater omentum is a very promising approach in defect-specific bone tissue regeneration. 7 This approach is based on tissue engineering strategies aiming Hendrik Naujokat and Johannes Spille contributed equally to this work.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. patient-specific bone reconstruction. 8 In this context, it has not been conclusively clarified in which surgical concept the scaffolds should be implanted into the situs as well as second step flap-harvesting.
The greater omentum is a highly vascularised tissue which enables excellent regenerative potential. It has already been established as a free graft for covering large and complicated soft tissue defects in head and neck surgery. 9 Furthermore, the omentum is rich in growth factors and progenitor cells, which enables sufficient proliferation and differentiation reactions whereby scaffolds could be suitable for autologous recellularization and implant in reconstructive surgery. 10 Harvesting the omentum is not associated with any functional deficit; however, open surgery as well as extensive laparotomy results in postoperative morbidity. Robot-assisted surgery is a modern minimally invasive surgical procedure that allows reduction of morbidity through the minimally invasive approach with at the same time excellent optical representation of the surgical field with high-resolution 3D view. 11 The aim of this study was to evaluate if robot-assisted surgery provides an advantage in the surgical management of scaffolds implantation into the greater omentum and second-step flap raising in facial skeleton reconstruction in regenerative medicine compared to open surgery.

| Study design
The study protocol was approved by the Ministry of Energiewende,

| Robot-assisted surgery
In this study a da Vinci Xi® surgical system in the Kurt-Semm-centre for laparoscopic and robot-assisted surgery at the university hospi-

| Open surgery
In conventional surgery the minipigs were placed in supine position and the greater omentum was accessed via a medial laparotomy at the upper abdomen with a safety distance of at least 2 cm to the xyphoid. The procedures for scaffold implantation (mobilising the omentum, placing the scaffolds, fixating the scaffolds) as well as harvesting the free flap were performed analogue to the protocol described above ( Figure 5).

| Statistical analysis
Statistical analyses were performed using SPSS (IBM®, Ehningen, Germany). Normally distributed and non-normally distributed F I G U R E 1 Score sheet to determine the animal objective recovery after the first operation NAUJOKAT ET AL.

| Surgery time and cutting length
The incision-suture-times of the single procedures are presented in

| Objective recovery time
The evaluation was performed with the developed score sheet for

| Flap raising
The surgical access for second stage flap raising was performed via the same access that the first stage. Exploration of the abdominal cavity did not reveal any adhesions, inflammatory change or organ lesion after scaffold-implantation. In all cases the scaffolds were

| DISCUSSION
Minimally invasive surgery has widely demonstrated its benefits in terms of shortened recovery and morbidity regarding abdominal operations. Initial disadvantages as limited manoeuvrability, the presence of rigid instruments and a restricted field of view have been overcome. 12 The da Vinci system was originally used in  abdominal and urological surgery and allows a 3D magnified vision through a binocular stereoscopic endoscope, higher degree of freedom of the instruments and movability of the robot arms in various angles even within confined spaces. 13 Therefore, application of robot-assisted surgery has been extended to various surgical disciplines and indications. 14 To the best of our knowledge, this study is the world-first report on scaffold implantation into the greater omentum for bone tissue engineering and flap raising using robot-assisted surgery. The duration for open surgery was nearly constant while in robot-assisted surgery the duration decreases with increasing number of procedures our study it was obvious that the duration of the whole surgical procedure using the da Vinci system was similar to that of conventional surgery after the learning curve. Moreover, it is described that robotic surgery can have a shorter learning curve than laparoscopy. 18 This enables many surgeons to perform laparoscopic approaches to complex procedures, if they would otherwise prefer open surgery and to ensure all patients the best operative treatment. 19 In some cases, surgical complications are detected only postoperatively, which increases the mortality and the risk for surgical malpractice. 20 In this study, no organ injuries, adhesions, or other surgical complications were detected while second-stage procedure for both surgical modalities. Nevertheless, advantages of the robotassisted surgery as tremor reduction, image magnification, and a stable camera platform lead to less tissue trauma and lower intra-  reconstruction of the facial skeleton. In the first human cases our group has implanted a titanium mesh filled with hydroxyapatite blocks loaded with bone marrow aspirate and bone morphogenetic protein-2, bone formation has been monitored by SPECT-CT and transplantation to the mandible was performed 3 month later. In this open procedure the upper laparotomy enabled good surgical access to the omentum without impairing adjacent organs, but the patient suffered from some morbidity at the first postsurgical days. 27 In these cases, the length of the laparotomy was more than 20 cm. The average length in this animal study was 11.6 cm. Robot-assisted surgery allow minimally invasive access and aesthetic favourable outcomes by small incisions and hiding scars in skin-wrinkles or in the navel. On the other hand, minimally invasive approaches limit the size of the scaffolds possible to implant and to harvest. In our study the scaffolds had a cylindric shape that passed through the 15 mm trocar.
Flap harvesting was not possible through the trocar, but through the same incision which had to be dilated only with minimal extend. To engineer a bone flap of a clinically relevant dimension, for example, for a mandibular segmental defect of 7 cm length with a more complex 3D shape, some scaffold-modifications would be needed to allow robot-assisted surgery: With the extent mentioned before, it would be desirable to disassemble the entire construct into several segments so that the corresponding scaffolds are implanted one after the other in a certain sort-order through minimally invasive trocars. 28 In the second-step the flap would be prepared as one peace (multiple scaffolds connected by vascularised omentum) and harvested through a small access like a string of beads (e.g. using an endocatch bag) and the entire construct would first be assembled extraabdominal. This multi-segment approach for bigger bone flaps for reconstruction of the facial skeleton is no longer a problem with today's CAD/CAM technologies. This animal study is a promising proof of concept that robot-assisted implantation (of more than one scaffold) is a helpful addition to current practice of bone regeneration in the greater omentum due to its minimally invasive approach.

| CONCLUSION
Despite its limitations, the current study showed that implantation of scaffolds into the greater omentum and second-step flap raising using da Vinci Xi system could be a feasible option. Bone tissue regeneration could benefit of robot-assisted surgery regarding surgical outcome, aesthetics, faster mobilisation, shorter hospital stays as well as reducing morbidity. However, further studies are needed to solve the challenge of engineered bone flaps of greater dimensions and the minimally invasive accesses.