JOURNAL OF ENDOUROLOGY
`Volume 25, Number 3, March 2011
`ª Mary Ann Liebert, Inc.
`Pp. 523–528
`DOI: 10.1089=end.2010.0306
`
`Differences in Grip Forces Among Various Robotic
`Instruments and da Vinci Surgical Platforms
`
`Phillip Mucksavage, M.D., David C. Kerbl, B.S., Donald L. Pick, M.D., Jason Y. Lee, M.D.,
`Elspeth M. McDougall, M.D., and Michael K. Louie, M.D.
`
`Abstract
`Introduction: The da VinciÒ surgical platform is becoming increasingly available and utilized. Due to the lack of
`haptic feedback, visual cues are necessary to estimate grip forces and tissue tensions during surgery. We directly
`Ò instruments using the three available da Vinci robotic surgical
`measured the grip forces of robotic EndoWrist
`platforms.
`Methods: Robotic instruments were tested in the da Vinci S, Si, and Standard systems. A load cell was placed in a
`housing unit that allowed for measurement of the grip forces applied by the tip of each robotic instrument. Each
`instrument was tested six times, and all data were analyzed using Student’s t-tests or analysis of variance when
`appropriate.
`Results: Slight differences in grip force were seen when the instrument was tested through 2 degrees of freedom
`at the tip ( p ¼ 0.02, analysis of variance) and when comparing a new instrument to an older instrument
`( p ¼ 0.001 at the neutral position). There was no statistical difference in grip force between the left and right
`robotic arms. There was a broad range of grip forces between the various robotic instruments. The lowest grip
`force was registered in the double fenestrated grasper (2.26  0.15 N), whereas the highest was seen in the Hem-
`Ò clip applier (39.92  0.89 N). In comparison to the S and Si, the Standard platform appeared to have
`o-lok
`significantly higher grip forces.
`Conclusion: Different grip forces were observed among the various robotic instruments commonly used during
`urologic surgery and between the Standard and the S and Si platforms.
`
`Introduction
`
`Approximately 200,000 surgical operations have been
`
`performed using the da Vinci robotic surgical system
`the last year, with >1000 robots now available
`over
`throughout the United States.1 An estimated 80% of all radical
`prostatectomies will be performed using robotic assistance in
`the upcoming year, while robot-assisted renal and bladder
`surgery volumes continue to increase.2–4 Despite the costs to
`acquire, maintain, and operate the platform, it has gained
`widespread acceptance as an alternative to many laparo-
`scopic and open surgical procedures.
`Although there are numerous studies examining robotic
`surgical outcomes and novel uses for the robot, very little is
`known about the inner workings of the robot. Few surgeons
`question the capabilities or limitations of the machine. We
`sought to help elucidate one of the most basic elements of the
`robot: the grip force of the robotic instruments. Using a load
`cell testing device, we investigated the specific grip forces
`Ò
`(closing pressures) exerted by the tips of various EndoWrist
`
`robotic instruments across the three commercially available
`da Vinci Surgical platforms.
`
`Methods
`A Standard da Vinci Robotic platform in an accredited ro-
`botic training center was used for the initial experiments. A
`2.2-mm button style compression load cell transducer (Inter-
`face Advanced Force Measurement, Scottsdale, AZ) was
`placed in a specially designed aluminum housing unit that
`allowed for the measurement of grip force for fine tipped
`instruments (Fig. 1). All instrument tips were placed in the
`middle of the housing unit with the tip extending to the
`shoulder of the shelved out platform (Fig. 2). Bulldog clamps
`were used to determine the force conversion factor inherent in
`the load cell housing unit by measuring the forces directly on
`the load cell and with the load cell within the housing unit.
`Initially, the differences in grip force at various wrist po-
`sitions, including the neutral position, positive and negative
`major deflection (deflection at
`the proximal wrist
`joint)
`
`Department of Urology, University of California–Irvine, Orange, California.
`
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`524
`
`MUCKSAVAGE ET AL.
`
`FIG. 1. Load cell and housing unit. The load cell (left)
`consists of a small circular disc connected by a wire to the
`interfaceÒ 9820 strain gage transducer (not pictured). The
`housing unit (right) holds the load cell in its long interior
`chamber for the testing of all robotic instruments.
`
`(Fig. 3), and left and right minor deflection (deflection at the
`distal wrist joint) (Fig. 4) were measured in a new (previously
`unopened) Maryland bipolar extended training instrument
`(8 mm) and an *3-year-old large needle driver (8 mm, ex-
`tended use training instrument). Once the wrist position was
`achieved, the housing unit was firmly grasped and move-
`ments of the instruments were deactivated by removing the
`head from the console visor. The new 8-mm Maryland bipolar
`grasper was also used to evaluated the left versus the right
`robotic arm, and was compared with an older (*2 years old)
`training instrument. All instrument trials were repeated six
`times at each EndoWrist position. Open surgical instruments
`
`FIG. 2. Experimental apparatus. A da VinciÒ Maryland
`Bipolar Forceps grasps the housing unit, which holds the
`load cell in place. All instruments were tested by gripping
`the middle of the housing unit with the tips fit tightly against
`the shoulder of the shelved out platform as seen above. The
`interface 9820 strain gage transducer can be seen in the
`background.
`
`FIG. 3. Side view of a da Vinci Maryland bipolar forceps.
`The neutral position is defined as being parallel to the in-
`strument arm, with no net displacement of the proximal or
`distal wrist joint. The positive major deflection is defined as a
`maximum upward or positive displacement from the neutral
`position via movement of the proximal wrist joint only. The
`negative major deflection is defined as a maximum down-
`ward or negative displacement from the neutral position via
`movement of the proximal wrist joint only.
`
`were also tested in a similar manner. The Aesculap Instru-
`ments (Long Kelly Curved, Product #: BH165R, Kelly Curved
`(Hemostat) Product #: BH135R, Baby-Mosquito Product #:
`BH115R, and Long Allis Product #: EA097R) were placed on
`the load cell housing and locked at one click. All instrument
`trials were repeated six times.
`Leak point pressure was determined using a similar setup
`described by Lee et al.5 A freshly harvested porcine renal ar-
`tery was occluded by the tips of an *2-year-old 8-mm Bowel
`grasper using the Standard robotic platform. Methylene blue
`dye mixed with saline was then infused through the artery at a
`constant rate of 30 mL=minute using an infusion pump. The
`maximum pressure in mm Hg required for leakage distal to
`the Bowel grasper was recorded using a Cole-Parmer (Vernon
`Hills, IL) digital pressure measuring device.
`A Standard, S, and Si da Vinci surgical systems were all
`available for testing at the same time and place during
`an American Urologic Association (AUA) robotic educational
`course at the University of California, Irvine. At this time,
`instruments commonly used during urologic surgery were
`tested across all platforms. All instruments were tested in the
`neutral position and each test was taken in triplicate. When
`comparing the S and the Si, the same instrument was used for
`each patient side cart and compared with the same type of
`instrument in the Standard system.
`Statistical analysis was performed using one-way analysis
`of variance and unpaired Student’s t-tests where appropriate.
`A p-value of <0.05 was considered significant. All statistical
`analysis was performed using STATA software, version 9.0
`(Stata Corp, College Station, TX).
`
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`GRIP FORCES IN ROBOTIC INSTRUMENTS
`
`525
`
`FIG. 4. Top view of a da Vinci Maryland bipolar forceps.
`The neutral position is defined as being parallel to the in-
`strument arm, with no net displacement via the proximal or
`distal wrist joint. The right minor deflection is defined as a
`maximum rightward—in this view upward—displacement
`from the neutral position via movement of the distal wrist
`joint only. The negative major deflection is defined as a
`maximum leftward—in this view downward—displacement
`from the neutral position via movement of the distal wrist
`joint only.
`
`Results
`A new Maryland bipolar grasper and large needle driver
`were found to have significant differences in grip forces at the
`neutral, major defection (positive and negative), and minor
`deflection (left or right) positions (Maryland p¼ 0.02, large
`needle driver p < 0.001, analysis of variance). Grip forces at the
`neutral position and minor deflections were not significantly
`different
`in both the Maryland grasper (neutral vs.
`left
`[p¼ 0.507] neutral vs. right [p¼ 0.147] right vs. left [p¼ 0.937])
`and needle driver (neutral vs. left [p¼ 0.357] neutral vs. right
`[p¼ 0.484] right vs. left [p¼ 0.999]). A significant difference did
`exist between the major deflections compared with the neutral
`and minor deflections in both the Maryland grasper and large
`needle driver (Fig. 5a, b). The total difference between the
`neutral position and average major deflections was 6.72% of
`the neutral position in the Maryland grasper and 4.3% in the
`large needle driver. These results were also confirmed with the
`Maryland grasper on the left arm (data not shown).
`The right and the left robotic arms were compared using
`the same instrument and found to be equivalent at each po-
`sition (Table 1). When compared with an older training in-
`strument, the newer instrument had a significantly higher
`grip force at each position (Table 1).
`Table 2 is a summary of all of the available training
`instruments tested on the Standard, S, and Si platform.
`Grip forces
`ranged from lowest
`(Double Fenestrated
`grasper 2.26  0.15 N) to highest (Hem-o-lokÒ clip applier
`39.92  0.89 N). There were no significant differences seen
`
`(a, b) Evaluation of the Maryland grasper (a) and
`FIG. 5.
`large needle driver (b) at the various wrist positions. *Sig-
`nificantly different from neutral and minor deflections. All
`data were converted into newtons and the Y axis has been
`scaled to show differences.
`
`when the same instrument was tested on the S and the Si
`surgical platforms; however, the Standard platform had a
`statistically significant higher grip force in most instruments
`when compared with the S and the Si. (Fig. 6).
`Leak point pressure was calculated using a bowel grasper
`and freshly harvested porcine renal artery. Leak point pres-
`sure was observed to be *830 mm Hg while using the 8 mm
`Bowel Grasper. Finally, commonly used open instruments
`were tested on the load cell as a reference point for compari-
`son to the robotic instruments. These findings are summa-
`rized in Table 3.
`
`Discussion
`Robotic surgery has quickly gained in popularity and ac-
`ceptance as an alternative to some open and laparoscopic
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`526
`
`MUCKSAVAGE ET AL.
`
`Table 1. Differences in Grip Forces Between
`Robotic Arms and New Versus Old Instruments
`
`Position
`
`Neutral
`Positive major
`deflection
`Negative major
`deflection
`Right minor
`deflection
`Left minor
`deflection
`
`Neutral
`Positive major
`deflection
`Negative major
`deflection
`
`Left arm
`in N (SD)
`
`8.91 (0.17)
`8.39 (0.11)
`
`Right arm
`in N (SD)
`
`8.78 (0.11)
`8.29 (0.31)
`
`8.28 (0.26)
`
`8.25 (0.21)
`
`8.89 (0.32)
`
`9.08 (0.10)
`
`8.98 (0.14)
`
`8.98 (0.14)
`
`Old instrument
`in N (SD)
`
`New instrument
`in N (SD)
`
`8.05 (0.36)
`7.53 (0.30)
`
`8.78 (0.11)
`8.29 (0.31)
`
`7.41 (0.57)
`
`8.25 (0.21)
`
`p-Value
`
`0.139
`0.501
`
`0.805
`
`0.204
`
`0.990
`
`0.001
`0.002
`
`0.007
`
`A new Maryland grasper was tested on the left or right robotic
`arms for grip forces at each position. A new Maryland grasper was
`tested versus an *2-year-old Maryland grasper. (Since earlier tests
`revealed no differences between neutral and minor deflection, these
`results were omitted.) All p-values were determined using unpaired
`Student’s t-tests.
`N¼ newtons; SD ¼ standard deviation.
`
`procedures. As the only commercially available robotic sur-
`gical platform, over 150,000 urologic procedures are expected
`to be performed with the da Vinci surgical system in the up-
`coming year.1
`The current robotic platforms do not employ the use of
`haptic feedback. Surgeons must use visual cues to estimate the
`
`force and tension placed on tissues and sutures during the
`operation. Although the lack of haptic feedback does not
`appear to increase tissue injury or result in poorer oncologic
`outcomes,6,7 the specific amount of force applied by the ro-
`botic instruments has never been examined. To our knowl-
`edge, this is the first study directly measuring the grip forces
`exerted by the robot instruments on the three different plat-
`forms.
`We first examined the grip force at various angles afforded
`by the seven degrees of freedom. Minor deflections (move-
`ments along the distal wrist joint) and the neutral position
`exhibit the same amount of grip force, whereas major de-
`flections (movements at the proximal wrist joint) result in a
`significantly lower grip force. This was confirmed in the right
`and left hand as well as between two different instruments.
`Although these differences were significant, the actual grip
`force difference was only *5% of the neutral position in the
`Maryland grasper and Large Needle driver. As a result, this
`difference is unlikely to be of any major clinical significance.
`Differences also existed between new instruments and old
`instruments. It is not surprising that a previously unused in-
`strument had a significantly higher grip force at all grasping
`angles compared with the same older instrument. In our trials
`we tested an extended use training instrument that had been
`used for over 2 years and compared it to an unused instru-
`ment. The actual differences were statistically significant, but
`by <10% in the neutral position for the new instrument. In a
`clinical setting where most EndoWrist instruments are limited
`to 10 uses, it is unlikely that these differences would be noted.
`More importantly, grip force between the left and right
`arms of the robot did not differ when using the same instru-
`ment. Significant differences were observed among the vari-
`ous EndoWrist instruments and varied widely among the
`different types of instruments. Grasping or tissue handling
`instruments, such as the PK Maryland dissector and bipolar
`
`Instrument
`
`Standard N (SD)
`
`S N (SD)
`
`Si N (SD)
`
`p-Value
`
`Rank
`
`Table 2. Grip Forces for All Robotic Instruments Tested
`
`Double fenestrated grasper
`Bowel grasper (8 mm)
`Atrial retractor
`Grasping retractor
`Tenaculum forceps
`Long tip forceps
`PK dissecting forceps
`Fenestrated bipolar forceps
`Cadiere forceps
`Maryland bipolar forceps
`Resano forceps
`DeBakey forceps
`Round tip scissors
`Monopolar curved scissors
`Prograsp forceps
`Needle driver (5 mm)
`Large needle driver
`Suturecut needle driver
`Hem-o-lok clip applier
`
`2.26 (0.15)
`2.52 (0.19)
`3.11 (0.07)
`
`4.59 (0.19)
`6.67 (0.07)
`6.88 (0.16)
`7.62 (0.06)
`7.95 (0.38)
`8.76 (0.22)
`11.34 (0.52)
`11.38 (0.40)
`12.57 (0.33)
`12.10 (0.35)
`
`19.83 (0.52)
`21.64 (0.90)
`15.59 (0.13)
`37.57 (1.63)
`
`4.14 (0.28)
`
`3.78 (0.30)
`
`5.52 (0.13)
`
`5.74 (0.67)
`
`7.01 (0.35)
`8.54 (0.22)
`
`6.72 (0.20)
`7.77 (0.55)
`
`10.11 (0.96)
`10.38 (0.84)
`17.22 (0.53)
`
`17.74 (1.06)
`19.83 (0.29)
`39.92 (0.89)
`
`10.04 (0.34)
`10.38 (0.16)
`17.56 (0.36)
`
`18.49 (0.47)
`19.94 (0.17)
`38.00 (1.92)
`
`0.200a
`
`0.013b
`
`0.008b
`0.035b
`
`0.003b
`0.012b
`0.412a
`
`0.003b
`0.020b
`0.219b
`
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Low
`Medium
`Medium
`Medium
`Medium
`High
`
`All instruments were 8 mm unless otherwise stated.
`ap-Value determined by unpaired Student’s t-test.
`bp-Value determined by analysis of variance.
`Standard, da Vinci Standard Platform; S, da Vinci S Platform; Si, da Vinci Si Platform.
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`GRIP FORCES IN ROBOTIC INSTRUMENTS
`
`527
`
`FIG. 6. Comparison of grip forces in various instruments among different da Vinci robotic platforms. White bar ¼ da Vinci
`Standard; striped bar ¼ da Vinci S; gray bars¼ da Vinci Si; * ¼ Standard platforms significantly different from the Si and S
`platforms on post hoc analysis of variance test.
`
`Maryland, had less grip force compared with needle drivers
`and Hem-o-lok clip appliers. This suggests that they will
`produce less tissue trauma or injury during surgery.
`The Standard da Vinci surgical system displayed a signif-
`icantly higher grip force for nearly all of the instruments tes-
`ted when compared with the S and Si platforms. It was not
`surprising that the S and Si surgical platforms displayed
`similar grip forces among instruments, as much of the ad-
`vancement between the two systems is at the surgeon console
`and not the patient side cart; however, there were differences
`between the Si=S and Standard systems. Much of these dif-
`ferences in grip force (which again were small) could be the
`result of using instruments of differing ages. Alternatively, the
`differences may be a result of the construction of the Standard
`instruments or patient side cart.
`Using an 8-mm bowel grasper (which some surgeons may
`utilize on the fourth arm as a vascular clamp during a robotic
`partial nephrectomy), we occluded a freshly harvested por-
`cine renal artery and tested for leak pressures. When com-
`pared with the leak pressures reported by Lee et al.5 (who
`compared leak pressures in handheld Satinsky clamps and
`various bulldog clamps), the robotic leak pressures were
`greater than the bulldog clamps but less than the handheld
`Satinsky clamps. This suggests that using a robotic bowel
`
`Table 3. Open Instruments
`
`Instrument
`
`Force in newtons (SD)
`
`Long allis forceps (255 mm)
`Kelly curved forceps (160 mm)
`Kelly curved (Hemostat)
`Forceps (140 mm)
`Baby–mosquito forceps (100 mm)
`
`11.19 (0.10)
`32.48 (0.29)
`47.69 (0.42)
`
`70.10 (0.70)
`
`grasper as a vascular clamp may be safe and effective; how-
`ever, further testing, including histologic analysis, should be
`performed.
`Finally, we compared the obtained grip forces in common
`open instruments. Each open instrument set at one click, with
`the exception of the long 255-mm Allis, was much higher than
`the commonly used robotic instruments. This finding offers
`some reassurance that the robot is exerting less force when
`grasping tissue compared with commonly used open instru-
`ments.
`This study had some limitations, including the use of ex-
`tended use training instruments for most of the measure-
`ments, as well as the use of the Standard platform patient side
`cart that is over 5 years old. Extended use training instruments
`are not validated to maintain the programmed closing forces
`that are standard for clinically used instruments. Second,
`because of the small tips of the robotic instruments, a housing
`unit was manufactured to measure closing force, introducing
`another degree of uncertainty into the measurements. Finally,
`histological analysis of direct tissue damage was not per-
`formed. Despite these limitations, we feel that this article
`highlights the differences found in grip force among various
`robotic instruments, various robotic platforms, and at the
`various degrees of freedom. Future studies are needed with
`limited use patient instruments.
`The da Vinci robot is a major advancement in minimally
`invasive surgery, and urologists have been at the forefront in
`pursuing and utilizing this new technology. Although the
`current technology may be limited by the lack of direct haptic
`feedback, this study is the first to establish direct forces ex-
`erted by the robotic instruments. It provides an initial step in
`creating data that may eventually lead to the utilization of
`computer-generated haptics for the surgeon and may be im-
`portant for instrument selection during the delicate portions
`of an operation.
`
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`528
`
`MUCKSAVAGE ET AL.
`
`Conclusion
`Different grip forces were observed among the various
`robotic training instruments commonly used during urologic
`surgery and between the Standard and the S and Si platforms.
`The grip force of the robotic instruments tends to be less than
`that observed in comparable open surgery instruments, sug-
`gesting the general safety of robotic instruments in handling
`delicate urologic tissues. Further evaluation of the grip force
`of clinical, limited-use robotic instruments is needed.
`
`5. Lee HJ, Box GN, Abraham JBA, et al. Laboratory evaluation
`of laparoscopic vascular clamps using a load-cell device—Are
`all clamps the same? J Urol 2008;180:1267–1272.
`6. Coelho RF, Chauhan S, Palmer KJ, Rocco B, Patel MB, Patel
`VR. Robotic-assisted radical prostatectomy: A review of cur-
`rent outcomes. BJU Int 2009;104:1428–1435.
`7. Ficarra V, Novara G, Artibani W, et al. Retropubic, laparo-
`scopic, and robot-assisted radical prostatectomy: A system-
`atic review and cumulative analysis of comparative studies.
`Eur Urol 2009;55:1037–1063.
`
`Disclosure Statement
`No competing financial interests exist.
`
`References
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`1. Intutive Surgical. Annual Report 2008–2009; Jan 29, 2010.
`2. Brandina R, Gill IS. Robotic partial nephrectomy: New be-
`ginnings. Eur Urol 2010;57:778–779.
`3. Benway BM, Bhayani SB, Rogers CG, Dulabon LM, Patel MN,
`Lipkin M, Wang AJ, Stifelman MD. Robot assisted partial
`nephrectomy versus laparoscopic partial nephrectomy for
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`
`Address correspondence to:
`Phillip Mucksavage, M.D.
`Department of Urology
`University of California–Irvine
`101 The City Drive
`Building 55, Room 304
`Orange, CA 92868
`
`E-mail: pmucksav@uci.edu
`
`Abbreviations Used
`N ¼ newtons
`SD ¼ standard deviation
`
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