Ergon-trial: ergonomic evaluation of single-port accessversus three-port access video-assisted thoracic surgery

Luca Bertolaccini • Andrea Viti • Alberto Terzi

Received: 12 July 2014 / Accepted: 2 December 2014

� Springer Science+Business Media New York 2014

Abstract

Background Single-port access video-assisted thoracic

surgery (VATS), a technique progressively developed from

the standard three-port approach in minimally invasive

surgery, offers ergonomic advantages but also new chal-

lenges for the surgeon. We compared the ergonomics of

three-port versus single-port VATS.

Methods Posture analysis of surgeons was evaluated dur-

ing 100 consecutive VATS wedge resections (50 triportal vs.

50 uniportal). Technically demanding procedures (major

lung resection) were excluded. Operating table height,

monitor height, distance and inclination were adjusted

according to operator preference. Body posture was assessed

by measuring head–trunk axial rotation and head flexion.

Perceived physical strain was self-evaluated on the Borg

Category Ratio (CR-10) scale. Mental workload was asses-

sed with the National Aeronautics Space Administration–

Task Load indeX (NASA–TLX), a multidimensional tool

that rates workloads on six scales (mental, physical and

temporal demand; effort; performance; frustration).

Results All procedures were completed without compli-

cations. Head–trunk axial rotation was significantly reduced

and neck flexion significantly improved in uniportal VATS.

Viewing direction significantly declined (p = 0.01), body

posture as measured on the Borg CR–10 scale was perceived

as more stressful and the NASA–TLX score for overall

workload was higher (p = 0.04) during triportal VATS. The

NASA–TLX score for frustration was higher with uniportal

VATS (p = 0.02), but the score for physical demand was

higher in triportal VATS (p = 0.006).

Conclusions The surgeon can maintain a more neutral

body posture during uniportal VATS by standing straight

and facing the monitor with only minimal neck extension/

rotation; however, frustration is greater than with triportal

VATS.

Keywords Ergonomics � Physical workload � Mental

workload � Video-assisted thoracic surgery

With advances in instruments, techniques and imaging,

video-assisted thoracic surgery (VATS) has become the

surgical approach of choice for a still growing number of

procedures and plays a relevant part in minimally invasive

thoracic surgery. There are several advantages for patients

in undergoing VATS, including less postoperative pain,

shorter hospital stay and quicker return to normal everyday

activity [1]. Single-port access VATS, a technique pro-

gressively developed from the standard three-port

approach, was initially described only for minor thoracic

procedures [2] and then later applied in various other

procedures including lobectomies [3]. VATS not only

offers numerous benefits over conventional open surgery

but also poses ergonomic challenges for surgeons [4]. The

importance of ergonomics in VATS has been generally

recognized and previous studies have shown that ergo-

nomics and environmental factors can influence surgical

performance in laparoscopy; for instance, correct ergo-

nomic posture can reduce operating time [5]. Nevertheless,

as VATS gains wider acceptance, ways to improve the

ergonomics of the procedure will need to be found. To our

L. Bertolaccini (&) � A. Terzi

Thoracic Surgery Unit, Sacro Cuore Research Hospital, Via Don

Angelo Sempreboni 5, 37024 Negrar, Verona, Italy

e-mail: luca.bertolaccini@gmail.com

A. Viti

Thoracic Surgery Unit, S. Croce e Carle Hospital, Cuneo, Italy

123

Surg Endosc

DOI 10.1007/s00464-014-4024-6

and Other Interventional Techniques

knowledge, few studies have addressed ergonomic con-

cerns in VATS [4, 6, 7].

The aim of the Ergon-Trial was to compare the ergo-

nomics of VATS wedge resection with the standard trip-

ortal and the uniportal access techniques performed by

surgeons in a clinical setting. The two workloads com-

monly measured to assess the ergonomics associated with a

specific surgical task are the physical and the cognitive.

The physical workload measures the amount of physical

demand on the body, while the mental workload assesses

the amount of mental effort required to complete a surgical

procedure. The overall workload level is derived from

analysis of the physical and cognitive workloads.

Methods

Three right-handed surgeons skilled in VATS approaches

participated in the study. None reported physical com-

plaints such as carpal tunnel syndrome or serious neck or

back problems. Ergonomic analysis of the operating sur-

geon during 100 consecutive VATS wedge resections (50

triportal vs. 50 uniportal VATS) was performed. The

operating surgeon selected the surgical approach based on

the individual patient’s characteristics. Surgery for massive

pleural adhesions and technically demanding procedures,

such as major VATS lung resections, was excluded from

the analysis. Each surgeon carried out at least 15 proce-

dures with each approach, assisted by the same experienced

assistants. The instruments were identical for each type of

procedure. The operating table height and tilt and the

monitor height were adjusted for each surgeon. Based on

previous experience, the monitor was ideally placed in

front of the surgeon to permit a moderate downward

viewing angle of about 10�–30� without axial trunk rota-

tion [8]. For the scrub nurse, the monitor was ideally placed

just below eye level to allow a downward viewing direction

of 0� to about 15�. Upward viewing angles, which may

cause harmful neck extension, were avoided. For all par-

ticipants, minimal neck torsion was aspired. An axial

rotation less than *15� was considered ergonomically

acceptable. During all interventions, the patient was posi-

tioned in lateral decubitus contralateral to the lesion, with

the hip tilted backward approximately 5� and the shoulders

backward approximately 10�; both arms were placed for-

ward 90�, and the upside arm was bent at the elbow at 90�on the table for better lateral stability.

Depending on which surgical technique is performed,

two quite similar positions of the surgeon can be distin-

guished: in three-port access VATS (Fig. 1A), the surgeon

stands in front of the patient at the level of the chest, the

camera assistant stands on the same side and the scrub

nurse stands in front of the patient at the level of the

patient’s leg. Two monitors are located at the level of the

patient’s head, one in the surgeon’s line of vision and the

other in the line of vision of the scrub nurse. The trocars are

placed apart from the endoscope on both sides of the chest.

To handle the instruments, the surgeon must rotate his

upper body and lean over the patient. In the uniportal

VATS set up (Fig. 1B), the surgeon and the assistant must

be positioned in front of the patient in order to have the

same thoracoscopic vision throughout the procedure and

allow for more coordinated movements. The scrub nurse

stands on the opposite side. The incision, about 4–5 cm

long, is placed preferably in the fifth intercostal space in

the anterior position just inferior to the breast and pecto-

ralis major muscle [3].

Body posture was assessed with a video analysis system

consisting of a digital camera positioned above the surgeon

for observing the axial rotation of the head as compared

with the trunk and of the head flexion in the sagittal plane.

Measurements on the images were digitally performed with

a line angle measuring tool in Adobe Photoshop CC for

Linux (Adobe Systems Incorporated, San Jose, CA, USA).

The workloads were evaluated by subjective and

objective measures, in which the surgeon’s physical and

mental exertion during the procedures was self-assessed

during and after the operation and recorded. The eye height

and the viewing distance (eye-to-monitor) and the monitor

height in relation to the floor were measured to calculate

the viewing direction (Fig. 2) according to the ergonomic

equation [9]:

viewing direction = sineye height � screen height

viewing distance

� �:

The viewing direction is an ergonomic evaluation of the

combined effort of neck flexion/extension and the angle of

gaze performed by the extra ocular musculature [10]. For

the measurements in the sagittal plane, we used the ana-

tomic ear–eye line, running through the tragus of the ear

and the canthus of the eye. In the neutral position of the

head and neck, the ear–eye line has an inclined angle of

*15� to the horizontal [11]. When the head is in *10�flexion, the anatomic ear–eye line is *5� above the hori-

zontal [11].

Physical discomfort perceived during surgery was

measured by means of the Borg Category Ratio (CR-10)

scale, a widely accepted tool for evaluating physical

workload [12]. The general perception of physical exertion

comes from the integration of different symptoms arising

from active muscles, joints, possible pain, and dizziness.

The Borg CR-10 scale is a category scale with ratio

properties consisting of numbers related to verbal expres-

sions, which allows rate comparison between intensities as

well as the determination of intensity levels. The scale is

relatively simple to use; it is based on the surgeon’s

Surg Endosc

123

subjective estimation of physical strain experienced during

tasks (score from 1 to 10, where 1 indicates no strain and

10 indicates extremely uncomfortable and painful strain).

Seven areas of the surgeon’s body were evaluated: legs,

back, neck, right and left shoulder, and right and left

forearm. Perceived strain was scored every 10 min during

each operation to record changes over time.

On completing the operation, the surgeon evaluated the

cognitive workload according to the National Aeronautics

Space Administration–Task Load Index (NASA–TLX), a

widely recognized tool for self-reporting workload per-

ception [13]. The cognitive workload is a hypothetical

construct that represents the cost incurred by a human

operator to achieve a particular level of performance.

Because the definition of cognitive workload is human

centred rather than task centred, the cognitive workload is

defined uniquely by the demands of an objective task: as

such, it reflects multiple attributes that may have different

relevance for different individuals. The NASA–TLX rating

scale is a multidimensional assessment tool that allows

participants to rate their cognitive workloads on six scales

(Table 1): mental demand, physical demand, temporal

demand, effort, performance and frustration during task

execution [14, 15].

Statistical analysis

A power analysis was performed to calculate the sample

size for unpaired analysis; a sample size of at least 63

procedures was needed, with a type 1 error rate set at 0.05

and power at 0.80. Continuous variables are presented as

mean ± standard deviation. The two operational setups

were compared using Student’s t test or Wilcoxon’s two-

sample test (discrete or continuous data) and Pearson’s v2

test or Fisher’s exact test when appropriate (dichotomous

or categorical data).

The NASA-TLX consists of two parts: ratings and

weights.1 Ratings for each of the six subscales are obtained

from the subjects following the completion of a task. A

numerical rating ranging from 0 to 100 (from least to most

taxing) is assigned to each scale. Weights are determined

by the subjects’ choices of the subscale most relevant to

Fig. 1 Operative setup in the

Video-Assisted Thoracic

Surgery (VATS) suite.

A Operative setup in the

triportal VATS technique.

B Operative setup in the

uniportal VATS approach. AC

anaesthesia console, TC

thoracoscopic console, FS flat

screen, S surgeon, AS assisting

surgeon, SN scrub nurse, IT

instrument table

Fig. 2 Parameters measured to calculate the ergonomic equation of

viewing direction (an ergonomic evaluation of the combined effort of

neck flexion/extension and angle of gaze performed by the extraoc-

ular musculature)

1 NASA–TLX software is available for free download at tlx.play-

graph.com. Additional information can be found at humansys-

tems.arc.nasa.gov/groups/TLX.

Surg Endosc

123

workload for them from a pair of choices. The weights

are calculated from the tally of these choices from 15

combinatorial pairs created from the six subscales. The

weights range from 0 to 5 (from least to most relevant).

The ratings and weights are then combined to calculate a

weighted average for an overall workload score. The

significance level was set at 0.05 for all parameters. All

statistical analyses were performed using R Software

version 3.0.3.2

Results

The data on 100 consecutive VATS wedge resections (50

triportal vs. 50 uniportal VATS) were collected and ana-

lysed. All 100 VATS procedures were completed without

adverse events, major or minor complications. The average

operating time was 54 ± 13 min, with no significant dif-

ferences between the two techniques. Surgical indications

are shown in Table 2. The target tissue sites were the same

in all surgeries, which further minimized technical bias

between the two approaches (metastases were localized in

the upper lobes; wedge resection for interstitial lung

disease was performed in the lingula or middle lobe, while

pneumothorax was treated by wedge resection of the apex

of the lung in all cases).

For body posture assessment, the head–trunk axial

rotation, head flexion in the sagittal plane, and viewing

direction were successfully analysed for both techniques.

Head–trunk axial rotation was significantly reduced during

uniportal VATS (p = 0.03). The uniportal VATS settings

were found to significantly prevent neck extension, and the

viewing direction was significantly declined (p = 0.01).

The angle of gaze was not influenced by the settings

(p = 0.76) (Table 3).

Evaluation of physical discomfort on the Borg CR-10

scale showed that the body posture during triportal access

was perceived as significantly more stressful (p = 0.006),

particularly in the right shoulder (p = 0.006) and the back

(p = 0.02) (Table 4).

Table 5 presents the results of the NASA–TLX cogni-

tive workload assessment. The major difference was the

physical component, which was rated higher in triportal

than in uniportal VATS (47.47 ± 2.66 vs. 24.32 ± 5.53;

p = 0.006). The NASA–TLX score was significantly

higher for uniportal than triportal VATS, demonstrating

that the overall workload the surgeons experienced during

uniportal VATS was significantly greater than during

triportal VATS (39.71 ± 3.54 vs. 23.46 ± 29.92;

p = 0.041). The mental demand was rated higher for uni-

portal than triportal VATS (39.52 ± 3.21 vs.

28.94 ± 3.33; p = 0.20). Conversely, the physical demand

was rated significantly lower during uniportal than triportal

VATS (24.32 ± 3.53 vs. 47.47 ± 2.66; p = 0.0006). The

ratings for the temporal demand were substantially similar

for uniportal and triportal VATS (41.88 ± 3.63 vs.

40.67 ± 5.53; p = 0.89). The effort was rated significantly

lower with the uniportal than with the triportal VATS

settings (21.33 ± 4.52 vs. 48.72 ± 4.33; p = 0.001).

There was no significantly difference in performance

between uniportal and triportal VATS (37.13 ± 5.25 vs.

39.84 ± 4.94; p = 0.76). The NASA–TLX frustration

scale scores showed that frustration was significantly

greater with the uniportal than with the triportal VATS

setting (45.68 ± 3.64 vs. 26.24 ± 3.31; p = 0.02).

Table 2 Surgical indications for the 100 VATS wedge resections

Triportal VATS

(n = 50)

Uniportal

VATS (n = 50)

p value

Primary spontaneous

pneumothorax

23 28 0.48

Upper lobe lung

metastasis

6 4 0.53

Interstitial lung

disease

21 18 0.63

Table 1 Subscales and items on the NASA-TLX rating scale

Scale Description

Mental

demand

How much mental and perceptual activity was

required (e.g. thinking, deciding, calculating,

remembering, searching, etc.)?

Was the surgical operation easy or demanding,

simple or complex?

Physical

demand

How much physical activity was required (e.g.

pushing, pulling, turning, controlling, activating,

etc.)?

Was the surgical operation easy or demanding, slack

or strenuous, restful or laborious?

Temporal

demand

How much time pressure did you feel due to the rate

or pace at which the surgical operation elements

occurred?

Was the pace slow and leisurely or rapid and frantic?

Performance How successful do you think you were in

accomplishing the goals of the surgical operation?

How satisfied were you with your performance in

accomplishing these goals?

Effort How hard did you have to work (mentally and

physically) to accomplish your level of

performance?

Frustration

level

How insecure, discouraged, stressed, or secure,

gratified, content did you feel during the surgical

operation?

2 R is a free software environment for statistical computing and

graphics. It compiles and runs on a wide variety of UNIX platforms,

Windows and MacOS (www.r-project.org).

Surg Endosc

123

Discussion

There is no uniform consensus on port placement for

advanced VATS operations. The configuration is currently

dictated by the surgeons’ preference based on individual

experience. To facilitate instrument manipulation and

adequate visualization during thoracoscopy, trocars are

usually placed in a triangular fashion. This geometric

configuration allows the instruments to work at a 60�–90�angle with the target tissue, while trying to avoid the

problems with long-handled tools (too far or too near port

sites, chest wall interferences, etc.) [16]. In standard trip-

ortal VATS, the geometric configuration of a parallelogram

meddling with the optical source creates a plane with a

torsion angle that is ergonomically unfavourable. Likewise,

the operating team derives the visual feedback of the sur-

gical field from a monitor outside the operative field and

away from the patient [17]. Due to this position, the line of

vision is driven away from the line of action, creating a

difficult posture that may cause musculoskeletal com-

plaints [6]. On the other hand, one of the geometrical

advantages of single-port access VATS is the translational

alignment of instruments along the sagittal plane, bringing

them to reach the target lesion from a caudo-cranial per-

spective. Therefore, by taking better advantage of these

spatial and ergonomic features, surgeons can bring the

operative fulcrum inside the chest to approach the target

lesion in a fashion similar to open surgery [17].

The surgeon maintains a relatively static posture

throughout most of VATS, which, from an ergonomic point

of view, contributes to inefficiency [18]. Static postures

have been demonstrated to be more stressful than dynamic

positions, since muscles and tendons build up lactic acid

and toxins when held for prolonged periods in the same

position [18]. Moreover, the human body requires contin-

uous active control to maintain proper balance. However,

because two-thirds of the body mass are concentrated in the

upper part, this creates an unstable balance system.

Moreover, because the standing posture is similar to an

inverted pendulum [19], the position during quiet standing

actually relies on dynamic control even if the posture may

seem static [20]. Indeed, the increased workload caused by

poor ergonomics may substantially worsen the quality of

surgical performance [9, 21].

Despite the notable technical advances in thoracoscopic

surgery, little improvement in the surgeon’s working

environment has been made to reduce the physical strains

that this technique imposes [20]. Ergonomic studies have

shown that thoracoscopy is more static than open thoracic

surgery and recommended that postures during surgery

should be as neutral as possible when a prolonged static

posture is maintained throughout an intervention [7].

Our analysis suggests that the surgeon’s position during

uniportal VATS reduces muscular effort and spares the

involved joints (shoulder, forearm, etc.) from the excessive

traction otherwise required in the triportal approach.

Unfortunately, operating tables are not usually designed for

performing VATS, and tall surgeons find it very difficult to

lower the table to a height that would allow them to work

comfortably with a natural, neutral ergonomic posture.

This places an additional physical workload on the surgeon

Table 3 Ergonomic parameters for rotation, flexion and viewing

direction in 100 VATS wedge resections

Triportal

VATS

(n = 50)

Uniportal

VATS

(n = 50)

p value

Head–trunk axial

rotation (degree)

9.65 ± 5.45 2.13 ± 3.56 0.03

Head flexion in sagittal

plane (degree)

4.32 ± 1.23 3.46 ± 2.23 0.76

Viewing direction -15.47 ± 4.69 -4.26 ± 3.32 0.01

Table 4 Borg CR-10 scale scores for 100 VATS wedge resections

Triportal VATS

(n = 50)

Uniportal VATS

(n = 50)

p value

Neck 3.81 ± 1.03 3.45 ± 1.24 0.67

Shoulder

Left 3.84 ± 0.47 3.27 ± 0.14 0.50

Right 6.87 ± 1.31 4.02 ± 1.12 0.006

Forearm

Left 4.96 ± 1.31 5.24 ± 1.06 0.78

Right 5.12 ± 1.39 4.47 ± 1.64 0.51

Back 5.27 ± 0.89 4.51 ± 1.11 0.02

Legs 2.45 ± 0.44 2.34 ± 0.38 0.87

Overall 4.66 ± 0.94 3.86 ± 0.99 0.006

Table 5 Results of the NASA–TLX questionnaire in 100 VATS

wedge resections

Triportal VATS

(n = 50)

Uniportal VATS

(n = 50)

p value

Overall 23.46 ± 2.92 39.71 ± 3.54 0.04

Mental demand 28.94 ± 3.33 39.52 ± 3.21 0.20

Physical

demand

47.47 ± 2.66 24.32 ± 3.53 0.006

Temporal

demand

40.67 ± 5.53 41.88 ± 3.63 0.89

Effort 48.72 ± 4.33 21.33 ± 4.52 0.001

Performance 39.84 ± 4.94 37.13 ± 5.25 0.76

Frustration level 26.24 ± 3.31 45.68 ± 3.64 0.02

Surg Endosc

123

who is much more sensitive to physical strain than to

mental stress. While the burden of mental stress declines

with experience acquired through repeating procedures, the

strain perceived during the execution of physical tasks

remains bothersome, with the ensuing toll on these sur-

geons’ health causing concern for long-term consequences

unless preventive measures are taken. Furthermore, there is

evidence that physical discomfort during VATS is very

common [4, 7, 22, 23].

In the Ergon-Trial, we chose to observe only thoraco-

scopic wedge resection, since it is a frequently performed

and relatively short procedure with technically standard-

ized and clearly identifiable stages. For this surgical tech-

nique, we demonstrated that significant ergonomic benefits

may be gained in the uniportal VATS suite. In uniportal

VATS, the viewing direction is brought back to the path

orientation and restores the natural eye-hand-target axis

[10]. We also demonstrated that the physical workload is

significantly less challenging with uniportal than with

triportal VATS.

The physical demand, self-reported after performing

uniportal VATS, was rated significantly lower than after

triportal VATS. The body posture during triportal VATS

required more elbow flexion (causing prolonged activation

of the biceps) and more wrist flexion (causing greater fati-

gue). In particular, due to instrument manipulation and

interference from the surgical assistant (usually from his/

her arm supporting the camera), the surgeon has to raise and

abduct his shoulders, thus overloading the trapezius muscle.

In contrast, the more neutral ergonomic posture during

uniportal VATS may have resulted from manipulation

without influencing instrument movements [6, 7, 17, 24].

Cognitive workload assessment, as measured with the

NASA–TLX, demonstrated that the global workload score

was higher with uniportal VATS, primarily because of the

greater mental demand involved. These contradictory evi-

dences against uniportal VATS might have resulted from

familiarity and pre-existing expertise with the three-port

approach. Our performance analysis showed no statistically

significant difference in task performance between uniportal

and triportal VATS. Previous studies investigating laparo-

scopic surgical ergonomics were conducted with minimally

invasive surgery novices [21]. In contrast, the Ergon-Trial

involved only skilled surgeons to ensure that the subjects

already possessed the basic surgical skills needed to perform

the training tasks of varying difficulty levels. Novice sur-

geons, unfamiliar with basic surgical skills, would have

experienced greater mental workloads and thus introduced a

bias. The surgical results being equal, a surgeon skilled in

both uniportal and triportal approaches will most likely

prefer the one that provides better physical well being.

There are several limitations of this study. First, because

the trial was involved only three experienced surgeons at a

single centre, the results cannot be generalized to other

clinical settings. Second, only thoracoscopic wedge resec-

tion VATS was observed. Nonetheless, since VATS is

finding an ever-increasing role in the diagnosis and treat-

ment of a wide range of thoracic disorders, larger-scale

studies are desirable to better understand the ergonomics of

other common VATS procedures. Future research should

inform ergonomic guidelines for VATS and investigate the

effect of ergonomic interventions on physical and mental

workload.

In conclusion, the uniportal VATS setting can signifi-

cantly improve body posture during surgery: the surgeons

can stand straight facing the monitor with minimal neck

extension/rotation, thus benefitting from the ergonomic

advantages this setting offers. However, uniportal VATS

was associated with greater frustration.

Acknowledgments The authors thank Mario Viti, a gifted multi-

media artist, for his valuable help with the artwork. The authors

thank Dr. Diego Gonzalez Rivas who kindly offered to review this

paper.

Disclosures Luca Bertolaccini, Andrea Viti, and Alberto Terzi

declare no conflicts of interest or financial ties to disclose

References

1. Walker WS, Casali G (2008) The VATS lobectomist: analysis of

costs and alterations in the traditional surgical working pattern in

the modern surgical unit. Thorac Surg Clin 18:281–287

2. Rocco G (2012) One-port (uniportal) video-assisted thoracic

surgical resections—a clear advance. J Thorac Cardiovasc Surg

144:S27–S31

3. Gonzalez Rivas D, Fernandez R, De La Torre M, Martin Ucar AE

(2012) Thoracoscopic lobectomy through a single incision.

MMCTS. doi:10.1093/mmcts/mms007

4. Welcker K, Kesieme EB, Internullo E, Kranenburg van Koppen

LJC (2012) Ergonomics in thoracoscopic surgery: results of a

survey among thoracic surgeons. Interact CardioVasc Thorac

Surg 15:197–200

5. Joice P, Hanna GB, Cuschieri A (1998) Ergonomic evaluation of

laparoscopic bowel suturing. Am J Surg 176:373–378

6. Wauben LSGL, Van Veelen MA, Gossot D, Goossens RHM

(2006) Application of ergonomic guidelines during minimally

invasive surgery: a questionnaire survey of 284 surgeons. Surg

Endosc 20:1268–1274

7. Kranenburg L, Gossot D (2004) Ergonomic problems encoun-

tered during video-assisted thoracic surgery. Minim Invasive

Ther Allied Technol 13:147–155

8. Hanna GB, Shimi SM, Cuschieri A (1998) Task performance in

endoscopic surgery is influenced by location of the image display.

Ann Surg 227:481–484

9. Van Det MJ, Meijerink WJHJ, Hoff C, Totte ER, Pierie JPEN

(2009) Optimal ergonomics for laparoscopic surgery in mini-

mally invasive surgery suites: a review and guidelines. Surg

Endosc 23:1279–1285

10. Van Det MJ, Meijerink WJHJ, Hoff C, Van Veelen MA, Pierie

JPEN (2008) Ergonomic assessment of neck posture in the

minimally invasive surgery suite during laparoscopic cholecys-

tectomy. Surg Endosc 22:2421–2427

Surg Endosc

123

11. Seghers J, Jochem A, Spaepen A (2003) Posture, muscle activity

and muscle fatigue in prolonged VDT work at different screen

height settings. Ergonomics 46:714–730

12. Borg G (2008) A general scale to rate symptoms and feelings

related to problems of ergonomic and organizational importance.

G Ital Med Lav Ergon 30:A8–A10

13. Cao A, Chintamani KK, Pandya AK, Ellis RD (2009) NASA

TLX: software for assessing subjective mental workload. Behav

Res Methods 41:113–117

14. Noyes JM, Bruneau DPJ (2007) A self-analysis of the NASA-TLX

workload measure. Ergonomics 50:514–519

15. Hubert N, Gilles M, Desbrosses K, Meyer JP, Felblinger J, Hubert J

(2013) Ergonomic assessment of the surgeon’s physical workload

during standard and robotic assisted laparoscopic procedures. Int J

Med Robot Comput Assist Surg 9:142–147

16. Trejo A, Jung MC, Oleynikov D, Hallbeck MS (2007) Effect of

handle design and target location on insertion and aim with a

laparoscopic surgical tool. Appl Ergon 38:745–753

17. Bertolaccini L, Rocco G, Viti A, Terzi A (2013) Geometrical

characteristics of uniportal VATS. J Thorac Dis 5:S214–S216

18. Menozzi M, Von Buol A, Krueger H, Miege C (1994) Direction

of gaze and comfort: discovering the relation for the ergonomic

optimization of visual tasks. Ophthalmic Physiol Opt 14:393–399

19. Gage WH, Winter DA, Frank JS, Adkin AL (2004) Kinematic

and kinetic validity of the inverted pendulum model in quiet

standing. Gait Posture 19:124–132

20. Lee G, Lee T, Dexter D, Godinez C, Meenaghan N, Catania R,

Park A (2009) Ergonomic risk associated with assisting in min-

imally invasive surgery. Surg Endosc 23:182–188

21. Lee GI, Lee MR, Clanton T, Sutton E, Park AE, Marohn MR

(2014) Comparative assessment of physical and cognitive ergo-

nomics associated with robotic and traditional laparoscopic sur-

geries. Surg Endosc 28:456–465

22. Van Veelen MA, Nederlof EAL, Goossens RHM, Schot CJ, Ja-

kimowicz JJ (2003) Ergonomic problems encountered by the

medical team related to products used for minimally invasive

surgery. Surg Endosc 17:1077–1081

23. Psihogios JP, Sommerich CM, Mirka GA, Moon SD (2001) A

field evaluation of monitor placement effects in VDT users. Appl

Ergon 32:313–325

24. Lee G, Kavic SM, George IM, Park AE (2007) Postural insta-

bility does not necessarily correlate to poor performance: case in

point. Surg Endosc 21:471–474

Surg Endosc

123