Abstract
Objectives:
The use of three-dimensional monitors and digital microscopes for microsurgery is becoming prevalent and has great expectations of providing ergonomic advantages for surgeons. However, it remains unclear if this approach does provide ergonomic benefits, and whether transitional difficulties will be encountered when using it in place of a conventional optical microscope. Therefore, the purpose of this study was to clarify both the subjective and objective ergonomic advantages and the learning curve associated with the use of a digital microscope.
Methods:
Seventeen cases of head and neck reconstruction using a digital microscope were compared with those using a conventional optical microscope with respect to the time required for vascular anastomoses, microvascular complications, and ergonomics of the surgeon. The surgeons' learning curve was evaluated by comparing the time required for the transitions during the vascular anastomoses in each series. An objective ergonomics study was conducted by evaluating muscle fatigue using electromyography (EMG) during simulated vascular anastomosis.
Results:
The time required for vascular anastomosis transitions using a digital microscope gradually decreased in a linear fashion. In the objective study to check muscle fatigue by using EMG, a digital microscope was found to provide an ergonomic advantage for surgeons in the lower trapezius muscle part as compared to a conventional optical microscope.
Conclusions:
At present, a digital microscope provides modest ergonomic benefits to surgeons and requires a certain amount of time to learn.
Keywords: digital microscope, exoscope, 3D-monitor-assisted microsurgery, ergonomics, learning curve
Introduction
Since its development in the 1950s, surgical microscope has been imperative for microsurgery1). Despite mechanical improvements in optical microscope, surgeons have still been forced to view the operative field through binocular lenses with a stiff posture due to lack of consideration of human ergonomics2-4).
In recent years, digital microscopes projecting a high-definition image of the operative field onto a three-dimensional (3D) monitor have allowed surgeons to perform 3D-monitor-assisted microsurgery (3DMAM) with a “heads-up” style (Figure 1)5-8). These digital microscopes can generally be classified into three types: “Exoscope” type, which is derived from an endoscope, “Video camera” type, which eliminates the lens barrel, and “Hybrid” type, which has the functions of both optical and digital microscopes. Each of these provides different advantages: “Exoscope” offers a broad workspace over the operative field due to the small scope unit; “Video camera” provides high-definition images and high magnification through a video camera system with a high-performance image sensor; and “Hybrid” is advantageous for conservative microsurgeons who want to start 3DMAM with the backup of a familiar style. To date, six digital microscopes for 3DMAM are available in Japan: VITOM 3D (Karl Storz, Tuttlingen, Germany) and Visionsense (Medtronic, Minneapolis, MN, USA) as exoscope types, ORBEYE (Olympus, Tokyo, Japan) and Kestrel View II (Mitaka, Tokyo, Japan) as video camera types, and ARveo (Leica, Wetzlar, Germany) and KINEVO 900 (Carl Zeiss AG, Oberkochen, Germany) as hybrid types (Table 1). Previous studies have reported that digital microscopes have similar or superior usability compared to optical microscopes and offer optimal ergonomics for surgeons to prevent fatigue and damage to their necks9,10). However, few clinical studies have validated these findings in the field of reconstructive microsurgery, especially regarding surgeons' ergonomics.
Figure 1.
Representative intraoperative scenes of 3D-monitor-assisted microsurgery (3DMAM).
Above: 3DMAM using VITOM 3D classified as “Exoscope” type that does not interfere with the surgeon’s view toward the 3D monitor. Below left: 3DMAM using Kestrel View II classified as a “Video camera” type. Due to its large chassis and arm size compared to the exoscope, it is important to arrange the monitors so as to not disturb the views of both surgeons. Below right: 3DMAM using KINEVO 900 classified as a “Hybrid” type. The operator on the right side is watching the 3D monitor, and the assistant on the left side is viewing the operative field through an optical lens.
Table 1.
Classifications and Descriptions of the Digital Microscopes.
The aims of this study were to verify the usability of digital microscope in the field of reconstructive microsurgery compared to optical microscope and to evaluate the ergonomic advantages of 3DMAM both subjectively and objectively.
Methods
Between August 2018 and October 2020, five different digital microscopes evaluated that they had acceptable qualities for the microsurgery in the preoperative demonstrations used in 29 cases of free flap reconstruction by a single attending microsurgeon (YI). To standardize the conditions of the microsurgical procedures, this study included 17 cases of head and neck reconstruction in which arterial anastomosis was performed in an end-to-end fashion for the superior thyroid artery, the transverse cervical artery, or the lingual artery, and venous anastomosis in an end-to-side fashion for the internal or the external jugular vein. The consequent 17 cases used a digital microscope (3DMAM group), in which “Exoscope” (VITOM 3D, Visionsense) was used in seven cases, “Video camera” (Kestrel View II) in seven cases, and “Hybrid” (ARveo, KINEVO 900) in three cases. These were assessed with respect to the time required for vascular anastomoses, microvascular complications, and ergonomic advantage to the surgeon. Additionally, the data were compared with that of 17 cases of the same procedure administered under a conventional optical microscope (OME-8000; Carl Zeiss AG) during the same period (OM group). The ergonomics of each microscope was evaluated subjectively with a five-point scale (from 0, “none” to 4, “severe”) based on the existence of pain and/or stiffness in the head, neck, and back immediately after the completion of the microvascular anastomosis. The learning curve of 3DMAM was evaluated by measuring the transitions of the required time for vascular anastomoses in the 3DMAM group only. The results were analyzed by Fisher’s exact test for categorical data, independent two-sided t-test for continuous data, and Pearson’s product-moment correlation coefficient to examine the learning curves. The significance criterion was set at p < 0.05.
A prospective ergonomic study was also conducted. Five attending microsurgeons experienced at least over 30 cases of the microsurgery, wore wireless electromyography (EMG) sensors, and simulated vascular anastomosis with artificial vessels that had 1.0 cm diameters (Hagitec, Tokyo, Japan) for 15 min under a digital microscope (VITOM 3D) (3DMAM-sim group) or an optical microscope (OME-8000) (OM-sim group). Simulations using each microscope were conducted three times for each microsurgeon, and they were performed on different days to avoid bias for cumulative fatigue. A surface EMG system, TELEmyo DTS (NORAXON, Scottsdale, AZ, USA), was used to measure EMG, with a sampling frequency of 1500 Hz (Figure 2). The disposable electrodes of the silver and silver chloride type (Blue Sensor M; Ambu, Baltorpbakken, Denmark) were used. Frequency of bilateral sides of posterior cervical muscle fibers, upper trapezius muscle fibers, lower trapezius muscle fibers, and erector spinae muscle fibers was measured. The electrode attachment sites for each muscle were determined based on the recommendations of the SENIAM project (Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles) and were attached to the measured muscle after sufficient skin treatment. The distance between electrodes was set at 3.5 cm.
Figure 2.
The use of a TELEmyo DTS for objectively studying ergonomics.
Left: Small wireless EMG sensor and its multichannel receiver. Right: Eight EMG sensors attached to the surgeon’s neck and back.
MyoResearchXP (NORAXON) was used to analyze the surface electromyogram. The interval analysis consisted of 10 s of EMG signals immediately after the start of the procedure and at the 15-minute elapsed time point, excluding the large increase or decrease of amplitude in changing instruments and large motion. The median power frequency (MDPF) in each interval analysis was obtained by Fast Fourier Transform.
To compare the degree of fatigue before and after the procedure, the MDPF ratio was calculated by dividing the MDPF value at 15 min by the MDPF value at the beginning of the procedure in every muscle part. Non-parametric tests were performed on the MDPF ratios for each muscle part between the two groups of 3DMAM-sim group and OM-sim group. All statistical analyses were performed with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan).
Results
There were no statistical differences in patient demographics, flaps used, or recipient vessels between the OM and 3DMAM groups (Table 2, 3). However, the average time required for arterial anastomosis in the OM group (18.1 ± 5.2 min) was significantly shorter than that in the 3DMAM group (24.9 ± 6.5 min; p = 0.002) (Figure 3), whereas no significant differences were found in the average time required for venous anastomosis between the groups (p = 0.086). Although five instances of arterial thrombosis occurred intraoperatively in the 3DMAM group, there was no statistical difference between the two groups with respect to either intraoperative or postoperative complications. In regard to the learning curve, the time required for anastomosis in the 3DMAM group gradually declined in a linear fashion, whereas the OM group remained largely unchanged (Figure 4).
Table 2.
Demographics of the 3DMAM Group.
| Case | Diagnosis | Age (years) | Sex | Type of 3DMAM | Flap type | Recipient artery | Recipient vein | Intraoperative thrombosis | Postoperative thrombosis | Anastomosis time in artery (min) | Anastomosis time in vein (min) | Ergonomics score (points) |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 1 | Nasopharyngeal cancer | 71 | M | VITOM 3D | ALT | STA | IJV | – | – | 22 | 38 | 2 |
| 2 | Esophageal cancer | 61 | F | VITOM 3D | FJ | TCA | IJV | Artery | – | 32 | 27 | 2 |
| 3 | Hypopharyngeal cancer | 79 | M | Visionsense | FJ | STA | IJV | Artery | – | 31 | 29 | 3 |
| 4 | Nasopharyngeal cancer | 62 | M | VITOM 3D | ALT | STA | IJV | – | – | 28 | 22 | 1 |
| 5 | Hypopharyngeal cancer | 67 | M | Kestrel View II | FJ | TCA | IJV | – | – | 35 | 20 | 2 |
| 6 | Hypopharyngeal cancer | 72 | F | Kestrel View II | FJ | TCA | IJV | Artery | – | 25 | 34 | 2 |
| 7 | Hypopharyngeal cancer | 60 | F | ARveo | FJ | STA | IJV | Artery | Artery | 18 | 24 | 2 |
| 8 | Nasopharyngeal cancer | 79 | F | Kestrel View II | ALT | STA | IJV | Artery | – | 29 | 19 | 2 |
| 9 | Nasopharyngeal cancer | 67 | M | KINEVO 900 | VRAM | STA | IJV | – | – | 29 | 25 | 3 |
| 10 | Esophageal cancer | 58 | F | VITOM 3D | FJ | TCA | IJV | – | – | 23 | 16 | 2 |
| 11 | Nasopharyngeal cancer | 50 | F | VITOM 3D | ALT | STA | IJV | – | – | 14 | 22 | 2 |
| 12 | Hypopharyngeal cancer | 67 | M | Kestrel View II | FJ | STA | IJV | – | – | 19 | 20 | 1 |
| 13 | Esophageal cancer | 60 | F | Kestrel View II | FJ | TCA | IJV | – | – | 25 | 32 | 2 |
| 14 | Nasopharyngeal cancer | 54 | M | Kestrel View II | ALT | STA | EJV | – | – | 26 | 24 | 3 |
| 15 | Tracheal cancer | 75 | F | Kestrel View II | GOP | TCA | IJV | – | – | 18 | 28 | 1 |
| 16 | Lingual cancer | 66 | M | KINEVO 900 | ALT | STA | IJV | – | – | 34 | 30 | 4 |
| 17 | Esophageal cancer | 74 | M | VITOM 3D | FJ | LA | IJV | – | – | 15 | 24 | 2 |
ALT, anterolateral thigh flap; VRAM, vertical rectus abdominis myocutaneous flap; FJ, free jejunal flap; GOP, genicular osseous-periosteal flap; TCA, transverse cervical artery; STA, superior thyroid artery; LA, lingual artery; IJV, internal jugular vein; EJV, external jugular vein
Table 3.
Comparison and Statistical Results of Demographics, Time Required for Anastomosis, and Complications between the Two Groups.
| 3DMAM group (N = 17) | OM group (N = 17) | p-Value | |
|---|---|---|---|
| Male/female | 9/8 | 13/4 | 0.282 |
| Mean age | 66.0 ± 8.4 | 63.5 ± 12.2 | 0.496 |
| Flap types | |||
| FJ | 9 | 13 | 0.082 |
| ALT | 6 | 1 | |
| RAM | 1 | 3 | |
| GOP | 1 | 0 | |
| Recipient vessels | |||
| Artery | |||
| TCA/STA/LA | 7/9/1 | 5/10/2 | 0.781 |
| Vein | |||
| IJV/EJV | 16/1 | 17/0 | 1 |
| Average required time for anastomosis | |||
| Artery (end-to-end fashion) | 24.9 ± 6.5 | 18.1 ± 5.2 | 0.0023* |
| Vein (end-to-side fashion) | 25.5 ± 5.7 | 21.8. ± 6.4 | 0.0858 |
| Intraoperative thrombosis | |||
| Artery | 5 | 1 | 0.175 |
| Vein | 0 | 0 | 0 |
| Postoperative complications | |||
| Artery | 1 | 0 | 1 |
| Vein | 0 | 1 | 1 |
| Ergonomics score (from 0 “none” to 4 “severe”) | 2.17 ± 0.8 | 2.53 ± 0.8 | 0.231 |
*p < 0.05 was considered a significant difference.
Figure 3.
Comparison of the time required for anastomosis in the two groups.
A significant difference was seen in the artery part: OM group (18.1 ± 5.2 min) vs. 3DMAM group (24.9 ± 6.5 min) (p = 0.002).
Figure 4.
Transition time required for anastomosis in each group.
The required time for anastomoses in both arteries and veins gradually decreased in a linear trend in the 3DMAM group. The time in each case plateaued in the OM group.
There were no significant differences between the two groups of 3DMAM-sim group and OM-sim group in the subjective evaluation of ergonomics (2.17 ± 0.8 pts in the 3DMAM group vs. 2.53 ± 0.8 pts in the OM group; p = 0.231) (Figure 5). In objective research comparing MDPF ratio between the two groups using EMG, statistically significant differences were observed in the left lower trapezius muscle fibers (p = 0.029), but not in other areas (Figure 6).
Figure 5.
Subjective evaluation of ergonomics based on postoperative existence of pain and/or stiffness in the head, neck, and back.
Ergonomics scored on a five-point scale: 0 = none, 1 = light, 2 = moderate, 3 = heavy, 4 = severe.
Figure 6.
Objective analysis of ergonomics with EMG.
The value of MPDF ratio that consisted of 15 trials was compared between the 3DMAM-sim group and the OM-sim group. Only the lower trapezius muscle had significant difference (p < 0.05).
Discussion
Recently, digital microscopes consisting of a 3D digital video camera and a 3D monitor have been applied to the field of microsurgery7-9). Enabling microsurgical procedures with heads-up style, this visualization technology liberates surgeons from a cramped posture during microsurgery under an OM. Several subjective reports from the field of neurosurgery have reported ergonomic advantages for surgeons without conspicuous difficulty in microsurgical procedures compared to conventional techniques using OMs11,12). In this study, the usability of digital microscope compared to that of OM was verified in the field of reconstructive microsurgery.
Although previous studies have implied that the transition from optical microscope to digital microscope was not an issue for surgeons9,12), the average time required for arterial anastomosis in the 3DMAM group (24.9 ± 6.5 min) was longer than that in the OM group (18.1 ± 5.2 min). As all diameter of vessels for the anastomosis were over 2 mm, all types of digital microscopes used in this research had enough quality for the microsurgical procedures and did not affect the results depending on the types. The extra time required in the 3DMAM group indicates that surgeons need time to adjust to the slight but consequential mismatch of the perceived distance between the virtual images on the 3D monitor and the real subjects. The average time required for arterial anastomosis in the later nine cases (22.5 ± 6.6 min) was shorter than that of the initial eight cases (27.5 ± 5.3 min) in the 3DMAM group, but still longer than that in the OM group. The prolonged learning curve of the 3DMAM group may have been influenced by the variety of digital scopes used in this study. Indeed, a previous study found a 51% reduction in the required time for the arterial anastomosis after nine consecutive repetitions using a digital microscope in vivo13). Although model-specific features among optical products are negligible, there are considerable differences between digital microscopes with respect to operability, visibility, and resolution. These differences become more pronounced under the extra-higher magnification required for anastomosis of very small caliper (<1 mm diameter) vessels often encountered in reconstructive microsurgery.
Similar to the previous reports9,14,15), our subjective study showed improved ergonomics in the 3DMAM group, although this did not reach statistical significance. As MPDF has been suggested to be the most suitable parameters to measure EMG’s shift toward lower frequencies16), the MPDF ratio was adopted to the objective of the study in this research. There were also few significant differences in the objective analysis of ergonomics; however, the left trapezius muscle had significant differences (p = 0.029), and the right upper trapezius had certain trends of less fatigue in the 3DMAM-sim group. With respect to the surgeon’s posture during the microsurgery, the neck is not bent as much in OM as it is in 3DMAM because the binocular lens of OM is positioned almost horizontally with the surgeon's actual eye height and the stress for the lumbar area’s muscles to support the body when sitting on a chair was the same level in both 3DMAM and OM. These points are considered to lead to the result with no significant difference in the cervical and the erector spinae muscle’s regions. As for the upper and lower trapezius muscle’s regions, in OM, the surgeon’s head cannot be moved from the binocular lens, and the posture is not flexible due to the lens, whereas in 3DMAM, the position of the head and the shoulder can be freely adjusted to the favorable one for surgeons. Therefore, the trapezius muscles had certain trends of less fatigue in the 3DMAM-sim group and especially the lower left one had the statistical significance with respect to the MPDF ratio. The reason why there was no statistical significance in other muscle parts might be attributed to the number of participants, the reduced pressure on the subjects in a dry laboratory situation compared to a real operating room, the use of a footswitch placed on the right-side step in only the OM-sim group, and an inadequate amount of time (15 min) set for the anastomosis simulations. The duration for each simulation should have been longer to reproduce the clinical situations with reference to the average times required for anastomosis in the OM and 3DMAM groups.
The use of EMG to objectively study ergonomics provides a preliminary analysis of the potential benefits of a digital microscope. Further analysis of this new technology in a clinical setting will help to determine its true potential in the field of microsurgery.
Conclusion
Although the usability and reliability of digital microscopes could be improved for their use in reconstructive microsurgery, it appears that the rapid progress in technology will make the replacement of conventional optical microscopes inevitable, thereby aiding to alleviate the ergonomics concerns that have existed for over 70 years in microsurgery.
Author Contributions: Yuichi Ichikawa: Principal microsurgeon in the clinical study, planning the study methods, analyses of results, a subject of the ergonomics study.
Miho Tobita: Surgical assistance, a subject of the ergonomics study.
Rina Takahashi: Assistant of the ergonomics study.
Tomoyuki Ito: Surgical assistance, a subject of the ergonomics study.
Daiki Senda: Surgical assistance, digital microscope setup.
Rica Tanaka: Advisor of the manuscript.
Hiroshi Mizuno: A subject of the ergonomics study, revision and editing of the manuscript.
Kazufumi Sano: A subject of the ergonomics study, analyses of results, revision and editing of the manuscript, final approval of the article, and overall responsibility.
Conflicts of Interest: There are no conflicts of interest.
Statement of Approval from the Institutional Review Board: The retrospective study of microvascular anastomosis using a conventional optical microscope and a digital microscope was approved by the Institutional Review Board of Juntendo University Hospital on July 31, 2020 (Approval No. 20-101). The ergonomics study was approved by the Institutional Review Board of Juntendo University Hospital on June 6, 2020 (Approval No. 2020085).
Consent to Participate: The participants provided their written informed consent to participate in this study.
Acknowledgments
We would like to thank Masahiro Iijima, an electromyogram engineer, Youske Akiyama, an occupational therapist at Dokkyo Medical University Saitama Medical Center, Shuko Nojiri, a statistical advisor at Clinical Research and Trial Center in Juntendo University, and Toshiyuki Fujiwara, a professor in the Department of Rehabilitation Medicine, Juntendo University Graduate School of Medicine, for their assistance in the objective study of ergonomics.
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