Objective and subjective workload evaluation in the operating room: A study on DIEP Flap surgeries
Event Type
Oral Presentations
TimeWednesday, April 141:10pm - 1:30pm EDT
LocationHospital Environments
DescriptionSurgeons are attempting more complex procedures with potentially higher mental and physical demand as new procedures with new technology move the boundary of what is possible. This increases the risks of physical pain, burnout and development of musculoskeletal disorders (MSDs). Quantifying the physical and mental workload on surgeons will provide valuable information for targeted ergonomic intervention and it has received attention across various surgical sub-specialties in recent studies (Lowndes et al., 2018; Davila et al., 2018).
There is a wide range of different assessment tools to evaluate the workload and exposure to risk factors for work-related MSDs. Two well-known assessment tools are self-reports, and objective direct measurements (David, 2005). While self-reports (questionnaires, interviews, checklists, etc.) are subjective and their output depends on the participants’ self-evaluation, the direct measurements (e.g. electromyography (EMG), inertial measurement units (IMU), etc.) are objective. It is not easy to initially determine which assessment tool would best capture a specific occupation or task. Self-report methods have different advantages such as being easy to use, low-cost, and applicability in different situations (Li & Buckle, 1999; David, 2005). However, the participants’ comprehension of the question and their perception of exposure may not be accurate enough to make the results reliable (Spielholz et al., 2001; David, 2005). Thus, reliability and validity of self-reported methods have been reported to be too low for what we need as a basis for ergonomics interventions (Li and Buckle, 1999). Direct measurements as an objective assessment allow the data collection for different variables in large quantities and with high accuracy (David, 2005). However, it is not easy to measure all aspects of physical and mental workload using objective assessment tools. For example, pain, discomfort, or frustration is not objectively measurable using currently available technology. Also, using direct assessment tools inside the operating room (OR) may not always be feasible or practical. For example, attaching EMG sensors to the surgeons’ skin to collect their muscle activity during long surgical procedures is difficult as is anything below the elbow, like a galvanic skin response in the palms.

In this study, the surgeons’ workload during Deep Inferior Epigastric Perforator Breast Reconstruction Procedures (DIEP Flap surgery or autologous breast reconstruction) was evaluated using both subjective and objective assessment tools. The main goal was to validate the eligibility of both subjective (surveys) and objective (postural exposure using IMUs data) assessment tools inside the OR and to investigate their applicability and complementarity. The DIEP flap procedure is ergonomically challenging to surgeons as it is often a long and complex procedure, often lasting upwards of 12 hours. Different phases of the surgery each require different surgical equipment; in particular, the use of loupes and headlights during flap harvest and vessel dissection at the chest, as well as surgical microscopes (Howarth, 2018) during the anastomosis each have been associated with distinct ergonomic risks to the surgeon. Additionally, the DIEP flap procedure is typically performed with a larger team of two attending surgeons, two residents, and several surgical staff which further increases the resource needs during a DIEP flap procedure. We hypothesized that due to the complex nature of DIEPs that combine long surgical durations, use of adjunctive surgical equipment, and coordination between two surgeons and their staff, evaluation of workload during the DIEP flap procedure would require the use of both objective measurements (IMUs) and subjective measurements (surveys) in order to comprehensively evaluate the surgeon workload.
A survey was presented electronically to each of the attending surgeons following the completion of DIEP flap procedure. The survey contained six items from the NASA-TLX (Hart and Staveland, 1988) as well as items from the SURG-TLX (Wilson, et. al., 2011). Each item was rated on a scale from 0 (lowest) to 20 (highest). The survey covered different aspects of workload subscales including mental demand, physical demand, temporal demand, performance, effort, frustration, distraction, difficulty, and fatigue.
To measure the postures of surgeons during each DIEP flap surgery, IMUs were attached to the right arm, left arm, upper back, and head of each surgeon before the start of each case. From the IMUs, joint angles as a deviation from the vertical axis for each body part was calculated.

The basic statistics (mean and standard deviation (SD)) of the subjective and objective assessments were calculated. The relation between the physical demand from the survey and the postural exposure measured by the IMUs was evaluated using Spearman’s rank correlation coefficient.
Combined survey and IMU data were taken from two surgeons over a total of 7 cases for surgeon 1 and 9 cases for surgeon 2. Mean (SD) of the joint angles (degrees) were as follows: neck=23.7 (5.2), torso=17.4 (5.7), right arm=21.7 (8.2), and left arm=23.8 (11.6). The mean (SD) of the survey subscales were as follows: mental demand=12.7 (3.8), physical demand=12.8 (3.6), temporal demand=11.3 (3.3), performance=16.6 (2.3), effort=15.4 (2.8), frustration=10.6 (6.5), distraction=8.0 (6.1), difficulty=12.2 (3.5), and fatigue=13.3 (4.8).
There were no significant correlations between joint angles and reported physical demand. This may have occurred because the reported workload and the postures are measuring different aspects of the task, which indicates that there is need for both subjective and objective measures to evaluate complex surgical procedures.

Joint angles during surgery highlighted extremely flexed neck angles that could potentially led to an increased risk of developing musculoskeletal disorders. However, there was high variability in the joint angles which may have been a result of the complex nature of the DIEP flap surgery. The survey responses indicated that DIEP flap surgeries are associated with a moderately high workload. Collectively, our study highlighted the potential of using both subjective workload tools (surveys) and objective measures (postural data from IMUs) inside the OR to identify potential ergonomic issues in healthcare delivery. It was also shown that subjective physical demand was not significantly correlated to the postural data, suggesting that the two methods can assess different aspects of workload. It should be noted that one of the main goals of workload assessment are to design and recommend appropriate ergonomic interventions to prevent or mitigate the risk factors for MSDs. Both objective measurements and subjective assessments are helpful to ergonomists to design the most effective ergonomic interventions.


David, G. C. (2005). Ergonomic methods for assessing exposure to risk factors for work-related musculoskeletal disorders. Occupational Medicine-Oxford, 55(3), 190-199.
Davila, V. J., Weidner, T. K., Morrow, et al., (2018). RS10. Real-Time Ergonomic Issues in Vascular Surgeons: How We Are Hurting Ourselves While Operating. Journal of Vascular Surgery, 67(6), e242.
Hart SG, Staveland LE (1988). Development of NASA-TLX (Task Load Index): Results of Empirical and Theoretical Research. In: Hancock PA, Meshkati N (eds) Advances in Psychology, North-Holland, pp 139-183
Howarth, A.L., Hallbeck, S., Mahabir, R.C., et al.,(2019). Work-Related Musculoskeletal Discomfort and Injury in Microsurgeons, J Reconstr Microsurg, 35(5):322-328
Li, G. Y., & Buckle, P. (1999). Current techniques for assessing physical exposure to work-related musculoskeletal risks, with emphasis on posture-based methods. Ergonomics, 42(5), 674-695.
Lowndes, B. R., Forsyth, K. L., Blocker, R. C., et al.,(2018). NASA-TLX Assessment of Surgeon Workload Variation Across Specialties. Annals of Surgery, (September), 1.
Spielholz, P., Silverstein, B., Morgan, M., et al.,(2001). Comparison of self-report, video observation and direct measurement methods for upper extremity musculoskeletal disorder physical risk factors. Ergonomics, 44(6), 588-613.
Wilson MR, Poolton JM, Malhotra N, et al.,(2011) Development and validation of a surgical workload measure: the surgery task load index (SURG-TLX). World J Surg 35:1961-1969