therapeutic laparoscopy was incorporated into the practice of general surgery more than 25 years ago . since that time
, several modifications to minimally invasive access and surgery have been developed with the purpose of further minimizing surgical trauma and improving results : minilaparoscopy , computer - assisted robotic surgery , single - incision laparoscopic surgery , and natural orifice surgery .
the lack of clear improvement in overall safety , effectiveness , and value has kept these other approaches from replacing conventional laparoscopy .
smaller diameter ( 23 mm ) instruments , trocars , and scopes for use in procedures usually termed minilaparoscopy were introduced in the mid 1990s .
minilaparoscopy was promoted to minimize scarring , reduce postoperative pain , improve visualization in small fields , and improve surgical results , but it failed to become mainstream for a variety of reasons .
renewed interest in this approach has developed recently on the part of surgeons and medical device companies .
significant effort is being devoted to improving the ease of use , functionality , quality , and durability of minilaparoscopic instruments .
a novel design of mini instruments was recently developed and precisely manufactured to minimize friction between instruments and trocars ( 0.1 n vs. 4.3 n ) , based on exact experimentally determined optimal tolerances ( minimal gap between trocar and instrument ) and absence of trocar valves .
we conducted a study to evaluate these new low - friction mini instruments , comparing them to both 3-mm mini instruments and 5-mm traditional instruments , in a standardized set of simulation exercises .
the authors submitted the proposal for this study to the institutional review board at the university of pernambuco , and a full exemption was provided , with consideration that the study subjects were medical students and residents working in a dry lab setting , with no patients or patient data involved .
study participants were selected by testing surgical novices ( medical students ) and individuals with beginner  intermediate surgical experience ( postgraduate year [ pgy]-1 and -2 surgical residents ) ; excluding participants with known visual , motor , or other impairment ; excluding participants with prior advanced training in conventional or minilaparoscopy ( experts ) ; and training all study participants on all instrument designs , with at least 2 h of training occurring on 2 separate days .
we opined that the results would be cleaner and easier to interpret if we excluded surgeons who could have been expert in the use of any of the 3 instrument designs . including an expert in the use of any of the instruments could have biased that group toward that instrument , thus potentially confounding any actual differences attributable to the design .
based on pilot studies , it was determined that 22 medical students and 22 surgical residents would provide an adequate sample size to detect a difference in instrument performance ( power , 80% ; confidence level , 95% ; win episcope version 2.0 statistical software ; developed by the veterinary faculty , university of zaragoza , spain , and the department of animal husbandry , wageningen agricultural university , the netherlands ) .
the surgical simulator was selected for its recognized applicability , portability , and ease of use ( prodelphus e - knot , olinda , brazil ) ( figure 1a ) .
four standardized tasks were selected to simulate grasping , 2-handed movement , manipulation , and suturing , respectively : bean collection  grasping and moving 5 beans , one by one , into a bowl ; small rings  passing a suture through 5 variously oriented fixed metal rings ( eye bolts ) ; pearl necklace2-handed threading of a suture through four beads to create a necklace ; and suture and knot  passing a curved needle and suture through a laceration in a penrose drain , using a simple suture technique and a single square knot , with a 15-cm - long 5 - 0 polyglactin suture ( vicryl ; ethicon , sao paulo , brazil ) ( figure 2 ) .
a , the surgical simulator used for the 4 tasks ( prodelphus e - knot , olinda , brazil ) .
b , c , photographs of the 5-mm conventional laparoscopic instruments , 3-mm mini instruments , and 3-mm low - friction mini instruments ( karl storz endoscopy , tuttlingen , germany ) . b1 , 5-mm needle - holder ; b2 , 5 mm grasper forceps ; b3 , 5-mm maryland forceps ; b4 , 3-mm needle holder ; b5 , 3-mm grasper forceps ; b6 , 3-mm maryland forceps ; c7 , 3.5-mm - diameter , 15-cm - long low - friction mini trocar ; c8 , 3.8-mm - diameter , 15-cm - long conventional mini trocar ; and c9 , 6-mm diameter , 10.5-cm - long laparoscopic trocar .
four standardized tasks were selected to simulate grasping , 2-handed movement , manipulation , and suturing , respectively : a , collect beans  grasping and moving five beans , one by one , into a bowl ; b , small rings  passing a suture through 5 variously oriented and fixed metal rings ( eye bolts ) ; c , pearl necklace2-handed threading of a suture through 4 beads to create a necklace ; and d , suture and knot  passing a curved needle and suture through a laceration in a penrose drain , using a simple suturing technique and a single square knot with a 15-cm - long 5 - 0 polyglactin suture .
the conventional laparoscopic instruments ( 5 mm ) and trocars ( 6 mm ) and the conventional - friction mini instruments ( 3 mm ) and trocars ( 3.8 mm ) are commercially available from karl storz endoscopy ( tuttlingen , germany ) .
the low - friction configuration was created by replacing the conventional mini trocars with the new low - friction valveless trocars and retaining the same 3-mm mini instruments ( figure 1b , c ) . to increase precision of movement and decrease surgical stress for the surgeon and the patient during minilaparoscopic procedures , no seal or valve
is used with the novel low - friction trocars , thus minimizing ( essentially eliminating ) the usual friction forces between trocar and instrument .
the special trocar was designed to resemble a long needle , with very precise tolerances matching exactly the diameter of the corresponding 3-mm instruments . with this trocar system ,
the space between the instrument and the trocar is minimal , thereby eliminating the need for a rubber seal or valve to prevent gas loss .
these low - friction mini trocars ( 3.5 mm ) are also commercially available from karl storz endoscopy .
for each of the 3 instrument lines , the following instruments were chosen for use in this study : grasping forceps , curved maryland dissectors , and needle drivers .
the exercises were performed with the surgical trainer placed on a surgical table in a hospital operating room ( university hospital oswaldo cruz , recife , brazil ) .
they were randomly assigned to perform each of the 4 standardized tasks , with each of the 3 sets of instruments ( 5-mm , mini , and low - friction mini ) used in random order .
the order of tasks and instruments was randomized to avoid potential confounding by serial performance or learning effects .
data analysis was performed by two independent consultant biostatisticians who had no interest in the study outcome ( ulisses ramos montarroyos , university of pernambuco ; jose edmilson mazza batista , federal university of pernambuco ) . before the study was conducted , we decided to analyze the results for the 22 medical students and the 22 surgical residents as 2 separate groups .
the biostatisticians recommended that all 5 replicates for each exercise  instrument combination be included in the analysis ( there were insufficient outlier values to exclude highest and lowest values ) .
the data are graphically presented as mean ( sd ) for each exercise  instrument  participant group combination .
paired samples were compared by student 's t test ,  = 0.05 ( stata , version 12.0 ; statacorp , college station , texas ) .
the authors submitted the proposal for this study to the institutional review board at the university of pernambuco , and a full exemption was provided , with consideration that the study subjects were medical students and residents working in a dry lab setting , with no patients or patient data involved .
study participants were selected by testing surgical novices ( medical students ) and individuals with beginner  intermediate surgical experience ( postgraduate year [ pgy]-1 and -2 surgical residents ) ; excluding participants with known visual , motor , or other impairment ; excluding participants with prior advanced training in conventional or minilaparoscopy ( experts ) ; and training all study participants on all instrument designs , with at least 2 h of training occurring on 2 separate days .
we opined that the results would be cleaner and easier to interpret if we excluded surgeons who could have been expert in the use of any of the 3 instrument designs . including an expert in the use of any of the instruments could have biased that group toward that instrument , thus potentially confounding any actual differences attributable to the design . based on pilot studies ,
it was determined that 22 medical students and 22 surgical residents would provide an adequate sample size to detect a difference in instrument performance ( power , 80% ; confidence level , 95% ; win episcope version 2.0 statistical software ; developed by the veterinary faculty , university of zaragoza , spain , and the department of animal husbandry , wageningen agricultural university , the netherlands ) .
the surgical simulator was selected for its recognized applicability , portability , and ease of use ( prodelphus e - knot , olinda , brazil ) ( figure 1a ) .
four standardized tasks were selected to simulate grasping , 2-handed movement , manipulation , and suturing , respectively : bean collection  grasping and moving 5 beans , one by one , into a bowl ; small rings  passing a suture through 5 variously oriented fixed metal rings ( eye bolts ) ; pearl necklace2-handed threading of a suture through four beads to create a necklace ; and suture and knot  passing a curved needle and suture through a laceration in a penrose drain , using a simple suture technique and a single square knot , with a 15-cm - long 5 - 0 polyglactin suture ( vicryl ; ethicon , sao paulo , brazil ) ( figure 2 ) .
a , the surgical simulator used for the 4 tasks ( prodelphus e - knot , olinda , brazil ) .
b , c , photographs of the 5-mm conventional laparoscopic instruments , 3-mm mini instruments , and 3-mm low - friction mini instruments ( karl storz endoscopy , tuttlingen , germany ) . b1 , 5-mm needle - holder ; b2 , 5 mm grasper forceps ; b3 , 5-mm maryland forceps ; b4 , 3-mm needle holder ; b5 , 3-mm grasper forceps ; b6 , 3-mm maryland forceps ; c7 , 3.5-mm - diameter , 15-cm - long low - friction mini trocar ; c8 , 3.8-mm - diameter , 15-cm - long conventional mini trocar ; and c9 , 6-mm diameter , 10.5-cm - long laparoscopic trocar .
four standardized tasks were selected to simulate grasping , 2-handed movement , manipulation , and suturing , respectively : a , collect beans  grasping and moving five beans , one by one , into a bowl ; b , small rings  passing a suture through 5 variously oriented and fixed metal rings ( eye bolts ) ; c , pearl necklace2-handed threading of a suture through 4 beads to create a necklace ; and d , suture and knot  passing a curved needle and suture through a laceration in a penrose drain , using a simple suturing technique and a single square knot with a 15-cm - long 5 - 0 polyglactin suture .
the conventional laparoscopic instruments ( 5 mm ) and trocars ( 6 mm ) and the conventional - friction mini instruments ( 3 mm ) and trocars ( 3.8 mm ) are commercially available from karl storz endoscopy ( tuttlingen , germany ) .
the low - friction configuration was created by replacing the conventional mini trocars with the new low - friction valveless trocars and retaining the same 3-mm mini instruments ( figure 1b , c ) . to increase precision of movement and decrease surgical stress for the surgeon and the patient during minilaparoscopic procedures , no seal or valve
is used with the novel low - friction trocars , thus minimizing ( essentially eliminating ) the usual friction forces between trocar and instrument .
the special trocar was designed to resemble a long needle , with very precise tolerances matching exactly the diameter of the corresponding 3-mm instruments . with this trocar system ,
the space between the instrument and the trocar is minimal , thereby eliminating the need for a rubber seal or valve to prevent gas loss .
these low - friction mini trocars ( 3.5 mm ) are also commercially available from karl storz endoscopy . for each of the 3 instrument lines ,
the following instruments were chosen for use in this study : grasping forceps , curved maryland dissectors , and needle drivers .
the exercises were performed with the surgical trainer placed on a surgical table in a hospital operating room ( university hospital oswaldo cruz , recife , brazil ) .
they were randomly assigned to perform each of the 4 standardized tasks , with each of the 3 sets of instruments ( 5-mm , mini , and low - friction mini ) used in random order .
the order of tasks and instruments was randomized to avoid potential confounding by serial performance or learning effects .
data analysis was performed by two independent consultant biostatisticians who had no interest in the study outcome ( ulisses ramos montarroyos , university of pernambuco ; jose edmilson mazza batista , federal university of pernambuco ) . before the study was conducted , we decided to analyze the results for the 22 medical students and the 22 surgical residents as 2 separate groups .
the biostatisticians recommended that all 5 replicates for each exercise  instrument combination be included in the analysis ( there were insufficient outlier values to exclude highest and lowest values ) .
the data are graphically presented as mean ( sd ) for each exercise  instrument  participant group combination .
paired samples were compared by student 's t test ,  = 0.05 ( stata , version 12.0 ; statacorp , college station , texas ) .
the results are summarized in table 1 and are presented graphically in figure 3 , with means and standard deviations shown for every task  instrument  participant combination .
for all 4 tasks , the instrument design that performed the best was the same for both the medical student group and the surgical resident group . for the bean - collection
gross - grasping exercise , the 5-mm instruments performed best , followed by the low - friction mini instruments . for the other 3 more complex and precise exercises  small rings , pearl necklace , and suturing and knot  the low - friction mini instruments performed best , followed by the conventional mini instruments .
time to completion of the 4 tasks average times are shown in seconds ( mean  sd ) for the 3 laparoscopic instrument designs : 5-mm conventional laparoscopy , 3-mm conventional minilaparoscopy , and 3-mm low - friction minilaparoscopy .
the results of all comparisons  conventional vs. conventional mini , conventional vs. low - friction mini , and conventional mini vs. low - friction mini
average times for both participant groups are shown in seconds ( mean , sd ) for the 3 different laparoscopic instrument designs : 5-mm conventional , 3-mm conventional mini , and 3-mm low - friction mini .
all comparisons ( conventional vs. conventional mini , conventional vs. low - friction mini , and conventional mini vs. low - friction mini ) showed significant differences for all 4 tasks .
the potential advantages of minilaparoscopy are apparent and applicable to multiple stakeholders . to patients ,
the advantages of minilaparoscopy over traditional laparoscopy seem clear : smaller incisions , less scaring , and reduced postoperative pain . for surgeons ,
the transition from conventional laparoscopy to minilaparoscopy is intuitive : trocar and instrument positions are preserved , triangulation is maintained , operative technique is the same or similar , and the technical challenges inherent to natural orifice and single incision approaches are avoided . for payers and hospitals , there is no need to purchase giant equipment , and operating room costs are lower .
clinical studies have demonstrated some advantages of minilaparoscopy in technical feasibility , safety , effectiveness , and cost effectiveness for certain procedures . for laparoscopic cholecystectomy ( lc ) , sajid et al concluded in a meta - analysis that mini - lc results in less postoperative pain and better cosmesis than does conventional lc ; lima et al found a lower bile duct injury rate with mini - lc ; and carvalho et al demonstrated reduced hospital costs for clipless mini - lc .
for laparoscopic inguinal hernia repair performed by using a mini technique , lau and lee found , in a prospective comparative study , less postoperative pain , and carvalho et al found a shorter operative time . for transanal endoscopic microsurgery ( tem ) ,
araujo et al concluded that mini instruments provide improved visualization in this limited working space compared to conventional 5-mm instruments .
improved visualization within in a small space may have contributed to the better results for the suturing task in this study . as we can see , in the endoscopic view , visualization was improved with the 3-mm mini instruments versus that attained with the 5-mm instruments at the same vantage point ( figure 4 ) .
other clinical studies have found minilaparoscopy and conventional laparoscopy to yield similar outcomes . for mini - lc ,
for mini- versus conventional laparoscopic appendectomy , sajid et al found similar perioperative outcomes and hospital stay .
for hysterectomy , ghezzi et al found no difference in postoperative pain with mini- versus conventional laparoscopy .
none of these investigators used low - friction mini instruments , and none found standard - friction mini instruments to be inferior to conventional 510-mm laparoscopic instruments .
endoscopic views taken by a 10-mm 30 scope ( karl storz ) of the suture - and - knot task .
photographs were taken at exactly the same vantage point for ( a ) 5-mm and ( b ) 3-mm instruments . the better visualization obtained with the mini instruments can be observed
. why has minilaparoscopy failed to become more mainstream ? in an elegant study in a dry lab , rosser et al showed a decrease in the performance of laparoscopic surgeons when using early minilaparoscopic instruments when compared with traditional laparoscopic instruments .
early generations of 2- to 3-mm laparoscopic instruments had several mechanical limitations , including instrument bending , lack of insulation and electrocautery , suboptimal effector tip functionality , and poor durability .
as computer - assisted robotic surgery , single - incision laparoscopy , and natural orifice surgery appeared , but then struggled to replace conventional laparoscopy , a renewed interest developed in minilaparoscopy , causing surgeon - innovators and industry leaders to begin developing newer generations of mini instruments with improved performance .
the new low - friction trocars consist of an outside part , such as a needle , but are longer than the traditional mini trocars .
the insert , with a progressively dilating tip and minimal gap , causes less damage to muscle layers and skin during insertion than do traditional trocars . to facilitate placement
, the insert fits very firmly into a luer lock connector type that can also be used for suction or gas inflation and is specially useful for creating the retroperitoneal space for totally extraperitoneal ( tep ) hernia repair and lumbar sympathectomy .
research and development of these devices revealed that very narrow , exact clearances between precisely manufactured instruments and trocars would allow for the elimination of the co2 valve from the trocar .
doing so resulted in a decrease in instrument friction from 4.3 to 0.13 n , with minimum leakage of co2 ( 0.1 l / min ) .
early bench model tests of these low - friction mini instruments noted favorable surgeon perceptions .
the notable reduction of the friction forces between the trocar and the mini instruments results in less trocar movement and fewer trocar dislocations from the abdominal wall , which should reduce abdominal wall trauma and contribute to improved cosmetics results .
the experimental study reported herein was undertaken to test these low - friction instruments objectively , in a variety of simulated laparoscopic tasks , compared to both conventional minilaparoscopic instruments and conventional 5-mm instruments . in this study , for the bean - collection task ( a simple gross - movement exercise ) , the larger effector tips of the 5-mm instruments appeared to have the advantage over the smaller effector tips of the mini instruments .
it is of interest , however , even with this task , that the low - friction mini instruments outperformed the conventional - friction mini instruments .
for the other 3 tasks , all of which require 2-handed precise movements , the low - friction mini instruments outperformed either of the other 2 designs . in these experimental models ,
the low - friction design seemed to offer an advantage for precise coordinated surgical movements .
whether this same advantage will be observed with the clinical application of these low - friction trocars remains to be seen .
some early results from their application to mini - lc suggest that it may . the limitations of this study include those inherent in simulator - based basic research .
the participants ( intentionally ) included novices , beginners , and those with intermediate experience , not specialists in minimally invasive surgery .
metrics were time based only , with no metrics for efficiency of movement , surgeon ergonomics , or surgeon perception of the experience .
finally , the simulated surgical tasks were of various levels of complexity , but still were less complex than the human surgical experience .
in standard surgical simulator exercises , low - friction minilaparoscopic instruments outperformed both conventional 3- and 5-mm laparoscopic instruments in executing precise tasks .
 background and objectives : therapeutic laparoscopy was incorporated into surgical practice more than 25 y ago . 
 several modifications have since been developed to further minimize surgical trauma and improve results . 
 minilaparoscopy , performed with 2- to 3-mm instruments was introduced in the mid 1990s but failed to attain mainstream use , mostly because of the limitations of the early devices . 
 buoyed by a renewed interest , new generations of mini instruments are being developed with improved functionality and durability . 
 this study is an objective evaluation of a new set of mini instruments with a novel low - friction design.method:twenty-two medical students and 22 surgical residents served as study participants . 
 three designs of laparoscopic instruments were evaluated : conventional 5 mm , traditional 3 mm , and low - friction 3 mm . 
 the instruments were evaluated with a standard surgical simulator , emulating 4 exercises of various complexities , testing grasping , precise 2-handed movements , and suturing . the metric measured was time to task completion , with 5 replicates for every combination of instrumentexerciseparticipant.results:for all 4 tasks , the instrument design that performed the best was the same in both the medical student and surgical resident groups . 
 for the gross - grasping task , the 5-mm conventional instruments performed best , followed by the low - friction mini instruments . for the 3 more complex and precise tasks , the low - friction mini instruments outperformed both of the other instrument designs.conclusion:in standard surgical simulator exercises , low - friction minilaparoscopic instruments outperformed both conventional 3- and 5-mm laparoscopic instruments for precise tasks . 
INTRODUCTION
METHOD
Institutional Review Board Approval
Study Participants
Laparoscopic Simulation
Instruments
Data Acquisition
Data Analysis
RESULTS
DISCUSSION
CONCLUSION