Correspondence Address: Source of Support: None, Conflict of Interest: None DOI: 10.4103/0028-3886.355125
Source of Support: None, Conflict of Interest: None
Keywords: 3D printing, ergonomics, handle design, instrument, neuroendoscopy
The use of high-definition neuroendoscopes for minimally invasive neurosurgery has resulted in significant improvement in patient outcome. The smaller incisions result in less blood loss, less postoperative pain, minimal scarring, and faster recovery. However, these technological advancements of minimally invasive procedures have posed several challenges to the neurosurgeons. The image from the surgical site is transmitted to a monitor and surgery is performed through small operating channels. This results in loss of depth perception and eye–hand coordination. The entry hole acts a pivot point and results in movement of instruments in the opposite direction to the neurosurgeon's hand movements. This fulcrum effect leads to conflict between visual and proprioceptive feedback.
The current design of hand-held instrument in neuroendoscopy comprises of a finger grasping-based handle. It has one fixed and one moving ring at the handle, long shaft, and an end effector attached at another end of the shaft [Figure 1]. There are various types of end effectors with varying functionality used for cutting, grasping, punching, and dilating. Functionality is achieved by a push-pull rod-based mechanism assembled with the moving ring of the instrument. Literature shows that such design of neuroendoscopic instruments results in tendon and ligament stress, spinal deviation, and numbness of fingers., The difficulty of operating these neuroendoscopic instruments is further amplified due to limited maneuverability in the constrained environment. Several palm grasping-based handle designs have been developed and validated for other surgical branches such as laparoscopy, but there is very limited development for neuroendoscopic instruments., Palm grasping-based design of laparoscopy grasper shows that the palm grasp is preferable owing to its anatomical advantage to the surgeon, but it results in the higher pinch forces, which can result into unwanted damage to the tissues. Therefore, the optimal design of palm-based handle should provide an anatomical advantage to the surgeon as well as allow application of defined pinch force to the tissues.
The aim of the present study was development and validation of an ergonomically aesthetic handle with defined pinch force for endonasal trans-sphenoidal instruments of neuroendoscopy. The hypothesis of the study was that the palm grasping-based handle of biopsy forceps would result in ergonomic improvement and can lead to better task performance.
It involved obtaining design features by observing the endoscopic surgeries and from the analysis of the database of existing neurosurgical instruments. It was followed by computer-aided designing (CAD), obtaining concurrence from expert neurosurgeons, physical development, and simulation-based validation. From now onwards, the existing standard biopsy forceps with finger grasping will be referred to as control instrument and the modified biopsy forceps with ergonomic palm grasping handle as study instrument.
Hand clenching pattern was selected to hold and operate the end effector of the instrument. The contours of thenar and hypothenar eminence were measured from 10 adult subjects to decide the dimensions. The design parameters for the study instrument handle are shown in [Table 1].
The study instrument handle comprises a fixed part and a moving part connected with a riveted joint. The fixed part of the handle was designed to match the contour of the palm. At the moving part, a ring was made that provides a lock to prevent accidental falling of the instrument. Fingers recesses were provided at the moving part of the handle for better holding. The linear grip span of the instrument was kept as 80 mm. A double spring of 0.6 mm thickness was made for spring-back action of the handle. It allows self-retaining of the grasped objects with constant applied force and prevents unwanted damage due to the tissues.
The baseline data of the standard biopsy forceps was acquired from the virtual repository of neurosurgical instruments. The 3D model was imported into Siemens NX10 software (Unigraphic Solutions Inc, Plano, Texas, USA). CAD was performed to create the ergonomic handle design according to the design considerations. The STL file of the CAD model was exported for the fabrication of the study instrument using additive manufacturing [Figure 2].
Fabrication: Direct metal laser sintering
The study instrument was initially fabricated in ABS plastic material using FDM (Stratasys Dimension Elite 3D printer). The fabricated prototype was demonstrated to the expert neurosurgeons for their concurrence in the proposed design. Several alterations were made to the design based on their feedback and ABS prototypes were fabricated and the design was finalized. The finalized design was then fabricated in stainless steel material by direct metal laser sintering (DMLS). The working assembly of existing biopsy forceps was also fabricated using DMLS and assembled with the ergonomic handle. [Figure 3] shows the prototype of the assembled study instrument.
Testing of the instruments: Volunteers and tasks
Fifteen participants with no endoscopic experience were recruited after written consent that included novices, medical students, and neurosurgeons. The expert neurosurgeons were not included in the study to avoid the influence of the previous use of the control instrument. The ergonomic characteristics of the control and study instrument were assessed by performing defined grasp and pick-place activity on neuro-endo-trainer (NET). The selection of the instrument was random for each trial, and they performed the task on straight, left-tilt, and right-tilt of the activity plate using 0° and 30° endoscopes, respectively.
A Likert-like questionnaire [Table 2] was used to obtain the postexperiment feedback using the control and study instruments. The feedback was obtained on a scale of 0–10, where 0 is the least, and 10 is the highest score. The lower the score obtained in the Likert scale, the better was the instrument performance.
The performance evaluation of the control and study instruments was done by analyzing the videos of the activity on the straight plate (0° scopes) and tilted plate (30° scopes) of NET. The performance criteria were adapted from the Skills Assessment Scale score. The parameters used for comparison included (i) hitting events, hitting of the pegs or activity plate, (ii) tugging events, tugging of the ring while grasping or placing ring on the pegs, (iii) ring drops while moving the ring from one peg to another, (iv) jerky movements during the moving state of the ring, (v) average time taken for moving rings from one peg to another, and (vi) number of attempts for picking/grasping the ring from the peg.
The recorded video was analyzed by a neurosurgeon who was blinded to the subjects using an application developed for marking the performed activity [Figure 4]. The application has the provision for play and pause the video and record the events. The events were recorded for every frame, and the output of all the frames was stored in text file format for further analysis. The data was then loaded in MATLAB and categorized into the corresponding parameters for evaluation.
The subjective analysis included questionnaires 1–5 in which the scores were based on Likert scale for Q1–Q3. For objective evaluation, six parameters obtained from the video analysis of a pick and place activity were used to assess the performance of the control and study instruments. The cumulative value of Q1–Q3 and objective evaluation parameters were obtained and compared using the Mann–Whitney U-test to analyze the statistical significance, whereas for the qualitative variables obtained from Q4 and Q5, the percentages were used.
The statistical results for Q1–Q3 of the subjective evaluation parameters are shown in [Figure 5]. The results for question Q1 show the degree of difficulty of completing the task on the straight plate. The control instrument had a mean score of 5.60 and an SD of 2.23, whereas the mean score of the study instrument is 3.27 with an SD of 1.03. The difference was significant with P = .0061 and strongly favorable to the study instrument. The answers to question Q2 reported the degree of difficulty of completing the task on the tilted plate. The control instrument had a mean score of 6.13 and an SD of 2.29, and for the study instrument, mean score was 3.67 with an SD of 0.97. The P value was. 0010, and the result favors the study instrument. The intensity of the pain while using each instrument is reflected by the answers to question Q3. The control instrument had a mean score of 5.80 and an SD of 1.66, and the study instrument had a mean score of 3.00 with an SD of 1.13. The difference was significant with P = .0001 and is advantageous to the study instrument. [Table 3] shows the mean, standard deviation, and P values of the Mann-Whitney U Test obtained from the data analysis of subjective validation.
The answers to question Q4 addressed the preferences of the volunteers for using the self-holding feature of the study instrument. The answers to question Q5 addressed the preferences of the volunteers on the ergonomic handle and which instrument they would prefer for the same task. Out of 15 volunteers, 12 preferred the study instrument over the control for both these questions. The percentage of volunteers favoring the study instrument over the control instrument is 80%. The results show that the study instrument was ergonomically improved than the control instrument for the simulated surgical task.
The NET activity plate was kept at the median position, and the 0° endoscope was used to perform the task. The results of the video analysis were statistically analyzed. [Figure 6] shows the graphical representation of the six parameters compared for the control and study instrument on the straight activity plate.
The total number of hitting events of all participants was 115 for the control instrument, whereas for the study instrument, it was 36 (P = 0.0015). This shows that study instrument resulted in a significant decrease in hitting events. The total number of tugging events using the control instrument was 120, whereas for the study instrument, it was 39 (P = 0.00001). This shows that the use of study instrument resulted in a significant reduction in tugging events. For the ring-drop event, three subjects dropped rings once and one subject dropped the ring twice using the control instrument, whereas five subjects dropped the ring once using the study instrument (P = 0.8493). The number of jerks for control instrument was 16, and for the study instrument was 8 (P = 0.6312). The average time taken to move the ring using the control instrument was 19.57 s, and for the study instrument was 15.48 s (P = 0.1052). The number of picking attempts for the control instrument was 229, whereas using study the instrument was 194 (P = 0.0403). This shows that there was a statistically significant improvement in attempts to grasp the ring using study instrument.
The difference between ring drops, number of jerks, and average moving time was not significant. The cumulative values of the six parameters calculated from video analysis on straight activity plate are shown in [Table 4].
The NET activity plate was tilted to -30° and + 30° (randomly), and angled endoscope of 30° was used to perform the same task as in straight plate. A neurosurgeon examined the auxiliary video feed and marked events were statistically analyzed. [Figure 7] shows the graphical representation of the six parameters compared for the study and control instrument on the tilted activity plate.
The total number of hitting events for control instrument was 96 and using the study instrument was 60 (P = 0.0403). This shows that hitting events were significantly less using the study instrument. The tugging events using the control instrument was 106, and using the study instrument was 41 (P = 0.00001). This shows that the tugging remarkably reduced while using the study instrument. In the ring-drop events, four subjects dropped rings once, and one subject dropped the ring twice using the control instrument, whereas four subjects dropped the ring once using the study instrument (P = 0.7113). Considering the number of jerks in the movement of the ring from one peg to another, the total number of jerks were 24 using the control instrument and 16 using the study instrument (P = 0.3734). The average time taken to move the ring from one peg to another was 16.45 s using the control instrument and 15.33 s using the study instrument (P = 0.4532). The total number of picking attempts using the control instrument was 287 and using the study instrument was 208 (P = 0.0004), which shows that the study instrument performed better for picking the rings at the tilted plate and using high degree endoscope. The cumulative values of the six parameters on tilted activity plate are shown in [Table 5].
The results of the objective evaluation show that the study instrument performed significantly better for the parameters including hitting, tugging, and picking attempts. The jerks and average moving time also improved, but their results were not statistically significant and there was no difference in the ring drops.
The ring handle of endoscopic instruments has been reported to cause ergonomic discomfort to surgeons., The objective of the present study was to design and validate a novel ergonomic handle for neuroendoscopic instruments. Hand clenching is one of the most natural movements in humans. Hence, the ergonomic handle was designed to be operated by hand clenching movement to control the end effector. The handle was designed to naturally match the hand contours, and hence reducing the pressure zones of the traditional ring handle. The problem of higher applied force associated with existing palm-grasping-based handles was removed by using a double-leaf spring mechanism that allows exertion of constant applied force. However, the calculation of optimal applied force for grasping tissues needs further exploration to finalize the thickness of double-leaf spring.
The handle was compared with the typical ring handle configuration. The experimental NET trials have demonstrated the differences between the two handles in both subjective and objective validation studies. In subjective validation, most of the participants (80%) preferred the new design. Objective validation through the auxiliary camera video recording also showed improvement in the parameters including hitting, tugging, and picking attempts on both straight and tilted plates. However, the number of ring drops, jerks during the movement of rings, and the average time taken to move the ring did not improve significantly using the study instrument. These parameters may not able to reflect the ergonomic variations in the design and may include other variables including dexterity and skills involved in endoscopic procedures.
In literature, several studies have shown that palm grasping-based handle improves ergonomics and provides fine control for laparoscopy. The validation results also showed that the palm grasp-based handle results in improvement in the maneuverability during the simulated surgical tasks. Therefore, our study opined that palm grasp can provide the required finesse for neuroendoscopic surgeries. The study can be extended to the other neuroendoscopic instruments along with sensor-based evaluation of the ergonomics for parameters such as force, acceleration, and muscle fatigue.
A novel ergonomic handle for skull base neuroendoscopy was developed and validated. The findings of this study reveal that the hand clenching-based structure of the palm-grasping handle provides ergonomic advantages. It improves the usability of endo-nasal trans-sphenoidal neuroendoscopic instruments and provides stable operation by reducing the extreme motions of finger and thumb. The validation studies demonstrate that ergonomically designed study handle enhances the comfort of neurosurgeons and also lead to better task performance for the pick-and-place task. The study handle can also be used with the end effectors of other surgical instruments.
Financial support and sponsorship
This manuscript is the result of Research Projects funded by extramural grants from (i) BT/PR13455/CoE/34/24/2015 – Department of Biotechnology (DBT), Ministry of Science and Technology, Govt. of India, (ii) BT/HRD/35/01/01/2015 – Department of Biotechnology (DBT), Ministry of Science and Technology, Govt. of India, (iii) DHR/HRD/Support to Institute/Type-VIII (3)/2015 – Department of Health Research, Ministry of Health and Family Welfare, Govt. of India, (iv) SR/FST/LSII-029/2012 – Department of Science and Technology (DST), Ministry of Science and Technology, Govt. of India and (v) AI-37 - AIIMS-IITD Collaborative Research Project.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]