Microsurgical anastomoses were performed at our clinic’s microsurgery laboratory. The Symani was utilized for robot-assisted microsurgical anastomoses. This system provides wristed microsurgical and supermicrosurgical instruments, with motion scaling from 7 to 20 ×, tremor filtration, and increased range of motion through additional distal motion axes. The surgeon sits in a highly ergonomic chair and operates the system using wired controllers that resemble forceps, which can be freely moved and rotated while in an ergonomic position. All movements are transmitted with high precision and in real time to two robotic slave arms. The operating unit can be covered with sterile drapes and positioned above the desired operating field with flexibility.

The robotic digital microscope RoboticScope is a high-definition camera system that is connected to an augmented reality headset. It projects a high-quality, stereotactic image in front of the surgeon’s eyes, creating a three-dimensional live image. The surgeon’s head movements are converted onto the system through motion tracking using a multi-axis robotic arm. The surgeon can navigate through an augmented menu that appears on top of the operating field image using head gestures. This allows for the adjustment of zoom and focus, changes in orbital view, navigation through the operating field, and image/video recording completely freehand, without interrupting the surgery. The RoboticScope is equipped with a high-resolution camera, which was used for all video and photo recordings.

Participants were seated away from the operation table to perform the anastomoses, thereby being able to maintain an optimal ergonomic position.

Six experienced microsurgeons from our institution with more than 5 years of experience in free flap reconstruction participated in this study. Participants previously underwent a comprehensive training on operating the robotic systems and performed multiple anastomoses with the investigated approach until reaching a steady state in the preclinical learning curve. Each study attendee completed six robot-assisted microvascular end-to-end anastomoses on 1.0-mm-diameter artificial silicone vessels (WetLab, Japan) with six stitches of 10-0 sutures (Ethilon, Ethicon, USA), three on the frontside and three on the backside after flipping the vessel. Three anastomoses were performed with each suturing technique, respectively (see below). Silicone vessels were stabilized using a microvascular approximator on a foam training platform.

The steady-thread suturing technique (steady technique) and the switch-thread suturing technique (switch technique) are illustrated in Fig. 1 and Supplementary Video 1 and 2 for better understanding. The robotic micro dilator is operated with the non-dominant hand (in this study always the left hand), while the robotic micro needle holder with inbuilt scissors close to the joint of the instrument is operated with the dominant hand (in this study always the right hand).

Suturing techniques. Illustration of the essential steps of a the steady-thread suturing technique and b the switch-thread suturing technique. A detailed description of both techniques can be found in “Materials and methods”. Moreover, the techniques are demonstrated in Supplementary video 1 and 2

The steady technique describes the suturing technique, which is mainly used for conventional microanastomoses at our institution, and was adapted to the robotic approach. The long end of the thread is held with the needle holder and double-looped around the dilator. Then, the short end of the thread is grasped with the dilator and pulled through the loop. The long end of the thread is kept with the needle holder for the second and third knot. It is now single-looped around the dilator and the short end is pulled through again. Finally, it is single looped around the dilator in the opposite direction, the short end is pulled through and the thread is cut with the inbuilt scissors (Fig. 1a, Sup. Vid. 1).

The switch technique describes the suturing technique, which was proposed by the manufacturer for achieving square knots through robot-assisted suturing. The first knot is performed in the same manner as with the steady technique. However, then the long end of the thread is passed from the needle holder to the dilator and single-looped around the needle holder, which pulls the short end of the thread through the loop in the opposite direction. For the third knot, the long end is passed to the needle holder again and single-looped around the dilator, which grasps and pulls the short end. Finally, the thread is cut with the inbuilt scissors (Fig. 1b, Sup. Vid. 2).

In short, the main difference between the two techniques is whether the thread is kept with the same instrument for each knot to save steps and time (steady technique), or if it is passed between the instruments after each knot to prevent crossing and collision of the robotic instruments (switch technique).

During each microvascular anastomosis, the time to complete the anastomosis was recorded. Using video recordings, the total time per anastomosis was divided into the major steps of each anastomosis, which were analyzed separately: needle positioning, piercing, passage through vessel wall, knot tying, cutting of suture and additional time.

After finishing each anastomosis, participants had to fill out a questionnaire evaluating their subjective satisfaction with the anastomosis and the knot technique, as well as their satisfaction with the Symani performance, RoboticScope performance, and combined performance of both systems on a numeric rating scale from 0 to 10 (0 = minimum, 10 = maximum).

To assess the quality of microvascular anastomoses, the Anastomosis Lapse Index (ALI) was applied. This involved cutting the anastomoses longitudinally and photographing the inside. Deidentified and blinded photographs were analyzed by a single reviewer to identify specific types of errors and the total number of errors, that were previously described by Ghanem et al. (anastomosis line disruption, backwall or sidewall catch, oblique stitch causing distortion, bite leading to tissue infoldment, partial thickness stitch, unequal distancing of sutures, visible tear in vessel wall, strangulation of tissue edges, thread in lumen, large edge overlap) [17].

Furthermore, microsurgical skills using the different suturing techniques were analyzed by videorecording the procedures and evaluating the deidentified and blinded videos. An experienced microsurgeon used a modified version of the Structured Assessment of Microsurgery Skills (SAMS) by van Mulken et al. [18] to assess all anastomoses. The modified SAMS evaluates dexterity (steadiness, instrument handling, tissue handling), visuo-spatial ability (suture placement, knot technique) and operative flow (steps, motion, speed), as well as the overall performance and indicative skill level on a numeric rating scale from 1 to 5 (5 representing excellent skills).

Lastly, technical error messages generated by the Symani during anastomoses interrupting the workflow were recorded and quantified. Possible error messages included: master moved too quickly, device exceeded motion range, joint of device at pivot stop, master outside console workspace and device at workspace boundary. In addition, the number of threads torn unintentionally with both suturing techniques was counted and the total number of threads used per anastomosis was documented (only if the thread was too short after rupture, a new thread was used).

Statistical analysis was performed using GraphPad Prism (GraphPad Software Inc., USA). In all plots and bar charts, dots represent individual values with arithmetic mean and standard deviation. Statistical significance was assessed for surgical time, questionnaire items, ALI scores, SAMS scores and thread count using a two-way ANOVA when comparing multiple groups (corrected for multiple comparisons with Tukey and Sidak test, 95% confidence interval) and Student’s t-test when comparing the means of two groups (unpaired, two-tailed, 95% confidence interval). P values < 0.05 were considered statistically significant.