**4.1 Ovako working posture analysis system**

As during the performance of laparoscopic surgery a standing posture is adopted, it is important to regulate and adapt the height of the operating table, the height of the monitor, and its orientation and the space for the feet to be able to operate near the surface of the operating table to the morphological and functional characteristics of the surgeon. The placement of the elements in the surgeon's environment should facilitate the adoption of a comfortable posture, especially in the early stages of learning laparoscopic techniques, avoiding excessive inclinations and/or torsions of the trunk and head, as well as abduction of the shoulders. In this context, characterization studies of the adopted position and its consequences during simulations of laparoscopic operations have been carried out. In the first phase of performed studies, the application of the OWAS protocol [23] was used as a standardized process to characterize the level of risk for tasks and for postures that were forced, nonrepetitive, and without defined work cycles, taking into account the posture of the trunk, arms, and legs as well as depending on the level of the load or force exerted by the surgeon. This process allowed to assess the level of risk for surgeons caused by the maintenance of the analyzed postures for a prolonged period of time. The position of 13 surgeons (four women and nine men) with different levels of experience and specialties was analyzed. The surgeons performed a simulation of a 60-minute laparoscopic surgery at the Jesús Usón Minimally Invasive Surgery Centre, and the adopted position was coded every 20 seconds (**Figure 9**) using a 3D video photogrammetry.

The effective time of the operation was identified as the time during which the subject looks at the screen and handles the surgical instruments with both hands (**Figure 10**). Interruptions could be due to the training process, change in surgical instruments, change in simulation material in the pelvitrainer, and distracting attention.

In the obtained data (**Figure 11**), it can be observed that during the procedures, 12 of the surgeons adopted a posture with **level 2** risk, meaning that intervention is necessary, although not immediate.

The position of this level adopted by a greater number of surgeons sometimes during the intervention (**10 of the surgeons**) was coded as **2121**, which corresponds to a posture with the back inclined, the arms below the shoulder, and standing with both legs straight with a light load ≤10 kg. Furthermore, four surgeons adopted a posture with **level 3** risk of musculoskeletal injuries, implying that the working method should be modified as soon as possible. The posture of this level adopted by a greater number of surgeons sometimes during the intervention was coded as **4231**, which corresponds to a posture with the back bent and turned, one arm above the shoulder, standing with one straight leg, and with a force ≤10 kg. Only one surgeon adopted a posture with a **level 4** risk of musculoskeletal injuries, meaning that corrective measures must be taken immediately.

### **4.2 3D photogrammetry**

As observed previously, it is necessary to use instrumental techniques with a greater discriminatory capacity to characterize the position adopted by surgeons due to the fact that some movements such as bending and rotation of the trunk and head as well as flexion and abduction of the arms have been detected. 3D photogrammetry was utilized in order to quantify the posture of the body segments in 3D. The mechanical model (**Figure 12**) that was used to

**17**

**Figure 11.** *Report of risk levels.*

record the spatial coordinates of the anatomical markers (15 real + 3 virtual) was defined according to the standardized procedures of the kinematic analysis of the International Society of Biomechanics [24]. In this sense, the position was characterized in terms of the Euler angles [25] and the "Joint Coordination System" (JCS) [26], which allow to determine the variation of the orientation of a segment in three dimensions with respect to a local RS. Three markers associated with the monitor and three markers associated with the operating table were

added to the mechanical model (**Figure 12**).

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*

*Recorded surgery time. Blue: effective time and white: EMG record time.*

**Figure 10.**

**Figure 9.** *OWAS protocol (ergo/IBV software®).*

#### **Figure 10.**

*Recent Advances in Laparoscopic Surgery*

necessary, although not immediate.

video photogrammetry.

taken immediately.

**4.2 3D photogrammetry**

attention.

time. The position of 13 surgeons (four women and nine men) with different levels of experience and specialties was analyzed. The surgeons performed a simulation of a 60-minute laparoscopic surgery at the Jesús Usón Minimally Invasive Surgery Centre, and the adopted position was coded every 20 seconds (**Figure 9**) using a 3D

The effective time of the operation was identified as the time during which the subject looks at the screen and handles the surgical instruments with both hands (**Figure 10**). Interruptions could be due to the training process, change in surgical instruments, change in simulation material in the pelvitrainer, and distracting

In the obtained data (**Figure 11**), it can be observed that during the procedures, 12 of the surgeons adopted a posture with **level 2** risk, meaning that intervention is

The position of this level adopted by a greater number of surgeons sometimes during the intervention (**10 of the surgeons**) was coded as **2121**, which corresponds to a posture with the back inclined, the arms below the shoulder, and standing with both legs straight with a light load ≤10 kg. Furthermore, four

surgeons adopted a posture with **level 3** risk of musculoskeletal injuries, implying that the working method should be modified as soon as possible. The posture of this level adopted by a greater number of surgeons sometimes during the intervention was coded as **4231**, which corresponds to a posture with the back bent and turned, one arm above the shoulder, standing with one straight leg, and with a force ≤10 kg. Only one surgeon adopted a posture with a **level 4** risk of musculoskeletal injuries, meaning that corrective measures must be

As observed previously, it is necessary to use instrumental techniques with a greater discriminatory capacity to characterize the position adopted by surgeons due to the fact that some movements such as bending and rotation of the trunk and head as well as flexion and abduction of the arms have been detected. 3D photogrammetry was utilized in order to quantify the posture of the body segments in 3D. The mechanical model (**Figure 12**) that was used to

**16**

**Figure 9.**

*OWAS protocol (ergo/IBV software®).*

*Recorded surgery time. Blue: effective time and white: EMG record time.*


record the spatial coordinates of the anatomical markers (15 real + 3 virtual) was defined according to the standardized procedures of the kinematic analysis of the International Society of Biomechanics [24]. In this sense, the position was characterized in terms of the Euler angles [25] and the "Joint Coordination System" (JCS) [26], which allow to determine the variation of the orientation of a segment in three dimensions with respect to a local RS. Three markers associated with the monitor and three markers associated with the operating table were added to the mechanical model (**Figure 12**).

**Figure 12.** *Mechanical model used for the evaluation of posture by 3D photogrammetry.*

The sequence of turns used for the head was Zt-Yh-Xh (**Figure 12**) of the JCS method. Axes are defined as follows:


For the body segment of the shoulder, the sequence of turns Yt-Xh-Yh (**Figure 13**) of the Euler angles is as follows:


**19**

muscular effort.

**Figure 13.**

**4.3 Variability study: uncontrolled manifold analysis**

As a consequence of what has been described in Section 4.2, it is important to study the variability of the posture in order to test whether variability in upper limbs-joint configuration stabilizes or destabilizes head posture on the sagittal plane as its position is constrained by the displacement of the monitor during

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*

*Definition of the rotations of the right upper limb.*

The measurements performed to characterize the position adopted by surgeons

during the simulation of laparoscopic operations allowed for the first time to quantify the order of magnitude of the relative orientation of the body segments in laparoscopic surgery. The results obtained on the shoulder joint show that the range of the elevation angle oscillates between 11 and 46.1° with an average of 26.2° ± 7.8 (coeficient of varation (CV) 30%) for the skillful arm, while for the nonskillful arm, it varies between 9.1 and 52.6° with an average of 27.1° ± 10.1 (CV 37%). In both cases, the coefficient of variation is high, a fact that demonstrates the high variability in the position adopted by the surgeons during the surgical procedure as a consequence of the nonexistence of ergonomic criteria for the configuration of the work environment. A high percentage of surgeons operate with an elevation angle close to or greater than 30° associated with the appearance of local muscle fatigue in the shoulder as suggested by other studies [3, 27]; therefore, it is recommended that the range of elevation of the arms is below 30°. The position of the arm is directly related to the height at which the laparoscopic instruments are manipulated. These data suggest adapting the surgical environment to the characteristics of the surgeon taking into account the order of magnitude of the variability found in the studies performed. As regards the posture of the head, the following values were found: flexion of 14.76° ± 9.86 (CV 67%), extension of 2.8° ± 2.6 (CV 93%), left lateral inclination of 4.75° ± 4.09 (CV 86%), right lateral inclination of 10.71° ± 6.17 (86% CV), internal rotation of 14.21° ± 12.18 (86% CV), and external rotation of 9.31° ± 7.17 (77% CV). The results confirm that the head barely moves (range of motion) as a consequence of the observation of the monitor, and therefore, the muscles that intervene in the maintenance of the posture during relatively long time intervals can experience fatigue [28–30]. As could be seen so far, it is very important to take into account the high variability of the geometric parameters associated with the posture adopted by the analyzed surgeons. Therefore, the question arises whether this variability is "biopositive" or "bionegative" from the point of view of ergonomics and of the prevention of musculoskeletal pathologies of personnel as a consequence of postural and

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*

*Recent Advances in Laparoscopic Surgery*

method. Axes are defined as follows:

**Figure 12.**

movement takes place.

of the Euler angles is as follows:

positive).

The sequence of turns used for the head was Zt-Yh-Xh (**Figure 12**) of the JCS

ii.Yh axis of the head representing the axis with respect to which the right

iii.Xh axis has the direction of the "vector product" of the other two axes, representing the axis with respect to which the right (negative)/left (posi-

For the body segment of the shoulder, the sequence of turns Yt-Xh-Yh (**Figure 13**)

i.First rotation: the Yt axis of the coordinate system associated with the trunk that represents the axis with respect to which the azimuthal angle takes place

ii.Second rotation: the Xh axis of the humerus that represents the axis with respect to which the lifting movement of the humerus takes place (elevation:

iii.Third rotation: the Yh axis of the humerus that represents the axis with respect to which the internal (positive)/external (negative) rotation move-

(negative)/left (positive) rotation movement takes place.

tive) inclination movement takes place in the articulation.

(0° is abduction and 90° is forward flexion).

*Mechanical model used for the evaluation of posture by 3D photogrammetry.*

ment of the humerus takes place.

i.Zt axis of the coordinate system associated with the trunk, which represents the axis with respect to which the flexion (negative)/extension (positive)

**18**

**Figure 13.** *Definition of the rotations of the right upper limb.*

The measurements performed to characterize the position adopted by surgeons during the simulation of laparoscopic operations allowed for the first time to quantify the order of magnitude of the relative orientation of the body segments in laparoscopic surgery. The results obtained on the shoulder joint show that the range of the elevation angle oscillates between 11 and 46.1° with an average of 26.2° ± 7.8 (coeficient of varation (CV) 30%) for the skillful arm, while for the nonskillful arm, it varies between 9.1 and 52.6° with an average of 27.1° ± 10.1 (CV 37%). In both cases, the coefficient of variation is high, a fact that demonstrates the high variability in the position adopted by the surgeons during the surgical procedure as a consequence of the nonexistence of ergonomic criteria for the configuration of the work environment. A high percentage of surgeons operate with an elevation angle close to or greater than 30° associated with the appearance of local muscle fatigue in the shoulder as suggested by other studies [3, 27]; therefore, it is recommended that the range of elevation of the arms is below 30°. The position of the arm is directly related to the height at which the laparoscopic instruments are manipulated. These data suggest adapting the surgical environment to the characteristics of the surgeon taking into account the order of magnitude of the variability found in the studies performed.

As regards the posture of the head, the following values were found: flexion of 14.76° ± 9.86 (CV 67%), extension of 2.8° ± 2.6 (CV 93%), left lateral inclination of 4.75° ± 4.09 (CV 86%), right lateral inclination of 10.71° ± 6.17 (86% CV), internal rotation of 14.21° ± 12.18 (86% CV), and external rotation of 9.31° ± 7.17 (77% CV). The results confirm that the head barely moves (range of motion) as a consequence of the observation of the monitor, and therefore, the muscles that intervene in the maintenance of the posture during relatively long time intervals can experience fatigue [28–30].

As could be seen so far, it is very important to take into account the high variability of the geometric parameters associated with the posture adopted by the analyzed surgeons. Therefore, the question arises whether this variability is "biopositive" or "bionegative" from the point of view of ergonomics and of the prevention of musculoskeletal pathologies of personnel as a consequence of postural and muscular effort.

#### **4.3 Variability study: uncontrolled manifold analysis**

As a consequence of what has been described in Section 4.2, it is important to study the variability of the posture in order to test whether variability in upper limbs-joint configuration stabilizes or destabilizes head posture on the sagittal plane as its position is constrained by the displacement of the monitor during

conventional laparoscopy (LAP) and Laparoendoscopic Single Site (LESS) surgery approaches. Also, the introduction of a framework to quantify joint coordination and its influence on the posture adopted by surgeons seems to be relevant. Therefore, an uncontrolled manifold (UCM) hypothesis model has been proposed that allows to quantify, globally, kinematic variability in task-relevant and taskirrelevant components and to determine whether the analyzed laparoscopic tasks are performed in healthy ranges or not. The UCM provides a quantitative approach to analyze the influence of imposed constraints, e.g., workplace layout and instruments design on the postural strategy that surgeons choose to accomplish surgical tasks, and it allows to map the variance of three individual joint angles onto the head position variance. Also, it allows separation of the combinations of the mentioned angles that are equally able to stabilize the head position within an acceptable margin of error for those combinations that are irrelevant for the ongoing task (**Figure 14**).

The UCM framework has been used recently to examine whether teleoperation with the da Vinci Si Surgical System manipulator (grip fixture attached to master manipulator) changes the structure of joint variability relative to the freehand (holding the grip fixture alone) in experienced and novice surgeons [31] as well as to analyze whether joint angles cooperate to adjust head position during laparoscopy work [32] (**Figure 15**).

It was shown that the effect of teleoperation on hand movements' stabilization depends on experience and that the head control variable defines an uncontrolled manifold, i.e., joint configurations of upper arm during laparoscopy do not destabilize head position. The motor redundancy, due to the numerous degrees of freedom of the human locomotor apparatus, compared with the substantially lower anatomical constraints that are imposed by the structure of the musculoskeletal system at the level of the joints, gives the surgeons the possibility to adopt an infinite number of postures during work and consequently the ability to execute countless voluntary motor patterns in order to accomplish their tasks.

Eight right-handed experienced surgeons in laparoscopic surgery (>100 laparoscopic procedures) and LESS surgery (>20 procedures using LESS approach) voluntarily accepted to participate in the study. Subjects performed a dissection of the serosa layer on an ex vivo porcine stomach inside a laparoscopic box trainer for

**Figure 14.** *Mechanical UCM model.*

**21**

**Figure 15.** *UCM resume.*

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*

10 minutes. This task was carried out by both laparoscopic surgical approach (LAP) and by LESS surgery [33]. A 3D photogrammetry was used to calculate the spatial coordinates of anatomical markers, using the same model as described in Section 4.2. The 3D coordinates of digitized points were obtained using the algorithm known as direct linear transformation (DLT) and were specified with respect to the defined origin of the global reference system. The 3D coordinates were obtained for a total of 40 events (N = 40), an event in every 15 seconds of surgical activity. For the same events, the posture of the head was defined with respect to the trunk, considering posture as the position and orientation of body segments. The trunk and head body segments were defined as solids, and their spatial position and orientation were obtained fixing them to segmental reference frames (SRF). This process allows the measurement of the posture adopted by surgeons in terms of clinically interpreted position and orientation of body segments. The results of the study show that kinematic redundancy enables surgeons to adopt an appropriate posture during surgical tasks, allowing them to avoid uncomfortable postures. However, other constraints other than the anatomical ones may have an impact, in particular joint configurations, i.e., workspace layout and instrumental design. Therefore, the goal of the UCM analysis was to test whether variability in upperlimb joint configuration during two different surgery approaches stabilized or destabilized head posture on the sagittal plane. Although the intertrial variability in joint configuration space should be organized to stabilize manual operation-task movements, by definition, it could also be organized to stabilize other important controlled variables as well. The head posture is a plausible candidate as its position is constrained by the displacement of the monitor. The results of the UCM analysis showed a positive degrees of freedom synergy index indicating that the covariation of the upper-limb joint angles stabilizes the head posture of the surgeons in the anterior-posterior direction. This synergy is stronger in some surgeons (**Figure 16**). Even though the synergy index takes different values between the LAP and LESS approach (**Figure 17**), there was not a statistically significant difference in the synergy index between the LAP and LESS approach for the UCMs of both the left (t(7) = 1.76 and p = 0.12) and right joint spaces (t(7) = 0.127 and p = 0.902). As can be seen in the results of 3D kinematics of the posture of the head with respect to the trunk (**Figure 18**), there is a high variability of the postures adopted by

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*


*Recent Advances in Laparoscopic Surgery*

(**Figure 14**).

copy work [32] (**Figure 15**).

motor patterns in order to accomplish their tasks.

conventional laparoscopy (LAP) and Laparoendoscopic Single Site (LESS) surgery approaches. Also, the introduction of a framework to quantify joint coordination and its influence on the posture adopted by surgeons seems to be relevant. Therefore, an uncontrolled manifold (UCM) hypothesis model has been proposed that allows to quantify, globally, kinematic variability in task-relevant and taskirrelevant components and to determine whether the analyzed laparoscopic tasks are performed in healthy ranges or not. The UCM provides a quantitative approach to analyze the influence of imposed constraints, e.g., workplace layout and instruments design on the postural strategy that surgeons choose to accomplish surgical tasks, and it allows to map the variance of three individual joint angles onto the head position variance. Also, it allows separation of the combinations of the mentioned angles that are equally able to stabilize the head position within an acceptable margin of error for those combinations that are irrelevant for the ongoing task

The UCM framework has been used recently to examine whether teleoperation with the da Vinci Si Surgical System manipulator (grip fixture attached to master manipulator) changes the structure of joint variability relative to the freehand (holding the grip fixture alone) in experienced and novice surgeons [31] as well as to analyze whether joint angles cooperate to adjust head position during laparos-

It was shown that the effect of teleoperation on hand movements' stabilization depends on experience and that the head control variable defines an uncontrolled manifold, i.e., joint configurations of upper arm during laparoscopy do not destabilize head position. The motor redundancy, due to the numerous degrees of freedom of the human locomotor apparatus, compared with the substantially lower anatomical constraints that are imposed by the structure of the musculoskeletal system at the level of the joints, gives the surgeons the possibility to adopt an infinite number of postures during work and consequently the ability to execute countless voluntary

Eight right-handed experienced surgeons in laparoscopic surgery (>100 laparoscopic procedures) and LESS surgery (>20 procedures using LESS approach) voluntarily accepted to participate in the study. Subjects performed a dissection of the serosa layer on an ex vivo porcine stomach inside a laparoscopic box trainer for

**20**

**Figure 14.**

*Mechanical UCM model.*

10 minutes. This task was carried out by both laparoscopic surgical approach (LAP) and by LESS surgery [33]. A 3D photogrammetry was used to calculate the spatial coordinates of anatomical markers, using the same model as described in Section 4.2. The 3D coordinates of digitized points were obtained using the algorithm known as direct linear transformation (DLT) and were specified with respect to the defined origin of the global reference system. The 3D coordinates were obtained for a total of 40 events (N = 40), an event in every 15 seconds of surgical activity. For the same events, the posture of the head was defined with respect to the trunk, considering posture as the position and orientation of body segments. The trunk and head body segments were defined as solids, and their spatial position and orientation were obtained fixing them to segmental reference frames (SRF). This process allows the measurement of the posture adopted by surgeons in terms of clinically interpreted position and orientation of body segments. The results of the study show that kinematic redundancy enables surgeons to adopt an appropriate posture during surgical tasks, allowing them to avoid uncomfortable postures. However, other constraints other than the anatomical ones may have an impact, in particular joint configurations, i.e., workspace layout and instrumental design. Therefore, the goal of the UCM analysis was to test whether variability in upperlimb joint configuration during two different surgery approaches stabilized or destabilized head posture on the sagittal plane. Although the intertrial variability in joint configuration space should be organized to stabilize manual operation-task movements, by definition, it could also be organized to stabilize other important controlled variables as well. The head posture is a plausible candidate as its position is constrained by the displacement of the monitor. The results of the UCM analysis showed a positive degrees of freedom synergy index indicating that the covariation of the upper-limb joint angles stabilizes the head posture of the surgeons in the anterior-posterior direction. This synergy is stronger in some surgeons (**Figure 16**).

Even though the synergy index takes different values between the LAP and LESS approach (**Figure 17**), there was not a statistically significant difference in the synergy index between the LAP and LESS approach for the UCMs of both the left (t(7) = 1.76 and p = 0.12) and right joint spaces (t(7) = 0.127 and p = 0.902). As can be seen in the results of 3D kinematics of the posture of the head with respect to the trunk (**Figure 18**), there is a high variability of the postures adopted by

#### **Figure 16.**

*UCM synergy. (A) Left body side and (B) right body side.*

#### **Figure 18.**

*Results of variability of 3D neck rotation depending on monitor and trunk.*

the surgeons. This is due to the fact that surgeons are free to adopt their postures according to their personal judgment. Kinematics of surgeon heads' posture with respect to the trunk indicates high variability because of the adoption of the posture according to the subjective perception. Upper-body joint variability quantified using the framework of the UCM hypothesis allowed to separate the combination of joint angles that were equally able to stabilize mean head posture on sagittal plane for those solutions that destabilized head mean posture.

**23**

**Figure 20.**

**Figure 19.**

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*

**4.4 Inertial unit measurement system**

In the last few years, introduction and use of inertial sensors in the analysis and characterization of posture variability in the context of minimally invasive surgery has been a great advance in biomechanics methodology, as 3D photogrammetry requires a lot of time for digitation of images. This has been the most important reason for BioẼrgon Research group to record and analyze laparoscopic procedures in 3D using this technology, being a pioneer and probably the only one group to use it. Undoubtedly, this is much more an efficient instrumental technique for the characterization of posture in minimally invasive surgery [34]. In this sense, a study using the commercial system XSens MVN Biomech (**Figure 19**) was carried out in the Jesus Usón Minimal Invasive Surgery Center. Eight surgeons participated in the study (four novices and four experts) and performed 24 simple sutures with conventional instruments. The results obtained regarding the position of the surgeons corroborate the high variability found in the studies carried out with 3D photogrammetry. The values found show CV greater than 70% in all joints and especially in the wrist joint flexion-extension and radial and ulnar deviation (**Figure 20**).

*Sensorized surgeon with inertial measurement units (IMUs) and biomechanical model used by XSens.*

*Results from capture of surgeons' posture performing a simple suture.*

*Advanced Ergonomics in Laparoscopic Surgery DOI: http://dx.doi.org/10.5772/intechopen.84233*

*Recent Advances in Laparoscopic Surgery*

*UCM synergy. (A) Left body side and (B) right body side.*

**22**

**Figure 18.**

**Figure 16.**

**Figure 17.**

*LAP (left) vs. LESS (right).*

*Results of variability of 3D neck rotation depending on monitor and trunk.*

for those solutions that destabilized head mean posture.

the surgeons. This is due to the fact that surgeons are free to adopt their postures according to their personal judgment. Kinematics of surgeon heads' posture with respect to the trunk indicates high variability because of the adoption of the posture according to the subjective perception. Upper-body joint variability quantified using the framework of the UCM hypothesis allowed to separate the combination of joint angles that were equally able to stabilize mean head posture on sagittal plane
