Engineering, 2012, 5, 46-49
doi:10.4236/eng.2012.410B012 Published Online October 2012 (http://www.SciRP.org/journal/eng)
A Comparison of Pinch Force between Finger and Palm Grasp
tec hniques i n L ap aroscopic G ras ping
Susmitha Wi ls K1,4, George Mathew2, M. Manivannan3, Suresh R Devasahayam4
1Department of Biotechnology, Indian Institute of Technology Madras, India
2Faculty of Medicine, Universitas Pelita Harapan, Indonesia
3Department of Applied Mechanics, Indian Institute of Technology Madras, India
4Depar tm ent of Bio engineer ing , Chris tian Med ica l Co lleg e Vellore, I ndia
Received 2012
ABSTRACT
Laparoscopic surgery is a new abdominal surgical procedure which helps the patients in many ways like less hospital stay, faster
recovery and reduced pain. The main disadvantage in this surgical procedure is the reduced haptic perception by the surgeons due to
the usage of laparoscopic instrument to handle tissues which in turn cause damage of it as compared to an open surgery. The primary
aim of this investigation was to compare the pinch force applied during two different methods of laparoscopic grasping: Finger and
Palm grasp. A low cost force sensing resistor tailor made for the grasper tip was designed and fabricated for quantifying the grasper
tip force in the study. The results indicate more pinch force was applied during palm grasp as compared to finger grasp so as to pre-
vent the slippage of the tiss ues from the jaws of the laparoscopic grasper s.
Keywords: Pinch Force; Grasp ing; Laparoscopic Surgery; Fo r ce Sensing Resistor; Laparoscopic Grasper
1. Introduction
Minimally Invasive Surgery (MIS) is a modern surgical proce-
dure, which has made its presence felt since three decades and
is slowly replacing the conventional open surgery. Laparoscop-
ic surgery (LS) is one of the MIS techniques done in the abdo-
men with 3-4 small incisions through which surgeons insert
long handled laparoscopic instruments and laparoscope so as to
manipulate the target organ in the abdominal cavity [1,2].The
use of long handled instruments leads to reduced haptic percep-
tion which in turn may result in excess force being delivered at
the target tissue cau sing un wanted ti ssue damage. Laparo scop ic
graspers are one of the most indispensable instruments used for
grasping the target tissue in any laparoscopic procedure. The
force involved while grasping an object is the pinch force and
it’s defined as the force with which an individual holds/ grasps
an object without letting it slip off the grasper jaws. There are
two methods of grasping: Palm and Finger grasp [3]. In palm
grasp (Figure 1(a)), the palm of the operating hand rest on the
ring of the movable handle with the fingers 2-5 on the fixed
hand while in the finger grasp (Figure 1(b)), the thumb will be
inside the ring of the movable handle with other fingers on the
fixed hand opposing the thumb.
Sensorized laparoscopic tool with/without modification of a
commercial tool were used in various studies related to force
measurements [4-11]. Different types of force sensors used in
the MIS techniques with respect to their size, sterilizability etc
were explained in [12]. The objective of our study was to find
whether there is any significant difference in pinch force during
finger and palm grasping techniques in the laparoscopic surgic-
al setup. In this study an efficient force measurement arrange-
ment was setup using a cost effective custom made force sens-
ing resistor for tip pinch force sensing and strain gauges for
handle pinch force measurements.
2. Materials and Methods
An atraumati c fenestr ated lap aros cop ic grasp er was us ed for th e
finger and palm grasp pin ch force experiment. The grasper was
sensorized (Figure 2) and it consists of two force sensors. One
sensor was on the handle and another on the tip of the grasper.
Custom made force sensing resistor (FSR) was used as tip
pinch force sensor. FSR was developed with conductive foam
sandwiched between the copper sheets an d wires sold ered on to
these sheets were connected to the preamplifier circuit. The
sensor was designed in such a way that it fits to the grasper tip
and dimension was 2.2x0.4x0.1cm. The custom made FSR ex-
hibits decrease in the resistance as the applied force increases.
The sensor was calibrated by placing known weights on it and
has a sensitivity of 0.224V/N. Silicone gel and plastic sheet
were used to insulate the sensor from the conductive grasper tip.
In addition to the above sensor arrangement on the grasper,
strain gauge senso rs were attach ed to the handl e of it to get t he
handle pinch force. The handle of the grasper was assumed as a
Figure 1. Picture showing (a) Palm grasping technique (b) Finger
grasping techni que usi ng lapar os cop i c grasp er.

S. W. K ET AL.
47
Figure 2. Picture showing (a) Grasper handle attached with strain
gauges (b) Grasper tip attached with custom made FSR (c) Senso-
rized atraumat ic fenest rated l ap a ro scopic grasp e r.
cantilever and was filed and smoothened to ensure proper
placement of the strain gauge and for better sensitivity of the
sensor towards the applied force. The pair of foil type strain
gauges (EC-AL-3 FG1-120) from IPA Private Limited, Banga-
lore; were pasted one on each sides of the movable handle. The
strain gauge based cantilever arrangement was then calibrated
with known weights and has a sensitivity of 0.021V/N. The
connection from the sensors were taken to their respective
preamplifier circuit which was in turn connected to the USB
port of the computer, (where the signals were acquired for fur-
ther an alysis) through th e CMC DAQ (four ch annel data acqui-
sition system).
The experiment setup (Figure 3) for measuring the pinch
force while using the sensorized atraumatic fenestrated grasper
consists of an abdomen model (Turtle) from Ethicon Endo
Surgery, camera, TV monitor, four channels CMC DAQ and a
computer. Four different objects [PVC (O1), Foam (O2), Ethaf-
lex (O3) and Plexiglas s (O4)] of same dimensions (2x1x0.5cm),
shown in Figure 4, were placed inside the turtle. The subjects
were asked to grasp the objects for 20 seconds ensuring that the
grasped object did not slip off from the grasper jaws, the above
procedure was repeated for all the four objects using both finger
and palm grasping techniques. Also the subject was instructed
to operate the grasper using his/her right hand throughout the
experiment. Total of 10 subjects (3 females and 7 males) all
above 25 years of age volunteered for the experiment. The in-
clusio n criteri a for the subject s was that they have normal func-
tional hand and should be able to use a handle operated instru-
ment like a laparoscopic grasper without much physical dis-
comfort. The group excluded from volunteering in this study
were people with loss of sensory feedback in the arm, people
with tremors while holding objects and people lacking proper
visual feedb ack. Before acq uiring the pin ch force data, subjects
were asked to operate the laparoscopic grasper in finger and
palm grasping techniques to get comfortable using it so as to
avoid discrepancies in data due to subject’s anxiety. Statistical
analysis of the acquired data was carried out using SPSS 16.0
software. D ata of two tr ials were acquired for each subject and
the mean value of handle and tip pinch forces were found out
for all objects over the range of subjects, this was done for both
the grasping methods. The paired sample t- test were carried
out between the finger and palm grasp methods for both handle
and tip pinch forces.
3. Results and Discussions
Force profile for a subject grasping an object (O3) using palm
grasping technique is shown in Figure 5. The graph on the
upper half depicts handle pinch force and that on the lower half
depicts tip pinch force.
Figure 3. Step up for Pinch Force Measurement.
Figure 4. A pictu re of objects used for gras ping: (from left to right)
PVC (O1), Foam (O2), Ethaflex (O3) and Pl exigla s s (O4)
Figure 5. Handle and Tip Pinch Force profile for an object (O3)
grasped by a subject usi ng palm grasping technique.

S. W. K ET AL.
48
The handle and tip pinch force was found to be consistently
higher during palm grasp for all the grasped objects as com-
pared to finger grasp (Figures 6 & Figure 7).The Figures 6 &
Figure 7, represents the mean value of handle and tip pinch
forces in Newton with respect to the various grasped objects for
finger and palm grasping methods, respectively. The study
shows statistically a significant difference in tip pinch force
between the two grasping methods (p = 0.005) and also in the
case of hand le pinch force (p = 0.001) a greater sign ificant dif-
ference was obtained. The handle and tip pinch forces measured
while grasping; PVC (O1) and Plexiglass (O4) without slipping
were relati vely higher th an the other two obj ects. This observa-
tion was as expected as the first and fourth samples were rela-
tively hard materials as compared to Foam (O2) and Ethaflex
(O3) which are compressive. As is evident from the graph, it
was observed that the handle pinch force is much higher than
the tip pinch force this is in line with the findings reported by
researchers earlier [4]. A justification for the above observed
force pattern is the fact that the finger tips are innervated by
Figure 6. Mean handle pinch force for different objects grasped
using Finger and Palm graspi ng techniques .
Figure 7. Mean tip pinch force for different objects grasped using
Finger and Palm grasping techniques.
more number of mechanoreceptors as compared to the palm
[13] . And hence have a b etter n atural/ n eural feedback mechan-
ism that perceive the force felt on the handle which in turn is
the force act ual ly delivered to the t issu e at the tip. P alm grasp is
preferred to finger grasp due to its postural advantage as re-
ported by surgeons but it has the adverse effect of delivering
more force which may in tur n cause t issue d amage.
4. Conclusion
This study compared the pinch force for two laparoscopic
grasping techniques- Finger Grasp and Palm Grasp; it was ob-
served that the latter technique requ ires more forc e as compared
to the former. From the observed results it can be concluded
that even though palm grasp is preferable owing to its anatomi-
cal advant age to th e surgeon, it may cause un wanted d amage to
the target tissue and h ence finger grasp is preferabl e over palm
grasp from a patient safety point of view. The number of sub-
jects was limited to ten and the grasping technique was not
compared between experienced surgeons and novice. The ob-
jects grasped in th is study are rigid and elast ic which is not the
case in a normal laparoscopic procedure. Using viscoelastic
objects which closely depict animal tissue properties would be
necessary to get a better understanding of the procedure in real
surgical situations. An extended study on similar lines with
more number of participants, classified into surgeons and no-
vice with tissue mimicking objects for grasping would pave the
way for evolving safer laparoscopic procedures.
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