endoscopic surgery , either by laparoscopy or thoracoscopy , was achieved through a trocar that inserted into the cavity where the target organ was located . all surgeons were obliged to use trocars as long as they adopted the co2 gas insufflation method . because the first trocar was always inserted through the abdominal or chest wall , a risk has always been present of inadvertently injuring an abdominal or thoracic organ , as well as the possibility of bleeding . reusable trocars have the potential advantage of costing less than disposable trocars , if they can be used many times without losing the sharpness of the knife . dull reusable trocars might tear the abdominal wall much more than a sharp disposable trocar on insertion . injury on insertion of the trocar has been among the possible major complications of laparoscopic surgery . the safety shield system in which the knife popped in and out across the tip of the trocar was later developed , and this improvement has decreased injuries . however , a problem that surgeons can not ignore has remained in regard to the procedure for inserting the trocar : bleeding from abdominal wall muscles torn by the trocar knife . drops of blood along the trocar conceal the target organ from laparoscopic view and create problems for surgeons . in a french survey , we developed an ultrasonic ( us ) vibrating trocar , the sharpness of which was not diminished even with more than 900 repetitive insertions , overcoming the disadvantages of commercially available trocars , and also preventing bleeding from the tract at insertion . however , the friction due to movement of the obturator generated heat in the adjacent tissue along the insertion tract . therefore , we examined the degree of histological damage along the insertion tract and the recovery of abdominal wall tension by comparing port - site skin tensile strength with each trocar , in a porcine model . a generator and ultrasonic vibrating trocar ( olympus optical co. , tokyo , japan ) were used in this study . the frequency of the generator was set at 23.5 khz , the vibration amplitude at 150 m . the ultrasonic trocar is composed of an obturator , which conducts ultrasonic vibratory movements , and a trocar ( figure 1 ) . the diameter of the obturator is 12.6 mm , and the diameter of the trocar is 14.8 mm . swine were purchased from sumichiku limited , and six 9- to 11-week - old female swine were raised on specific - pathogen - free food for young swine purchased from shimizukou feed company . general anesthesia was achieved with midazolam ( yamanouchi , japan ) 0.2 mg / kg and medetomidine hydrochloride ( meiji seika , japan ) 40 g / kg for presedation , ketamine hydrochloride ( sankyo , tokyo , japan ) 10 to 15 mg / kg for induction , and isoflurane ( dainihon pharm . sodium sulbactam / sodium ampicillin ( 1.5 g ) was administered intravenously during the operation . veterinary ampicillin was administered orally ( 2 g / day ) for 5 days after the operation . the phantom was a block of swine muscle 200 mm x 300 mm x 35 mm . the ultrasonic trocar attached to a digital push - pull gauge ( aiko engineering co. , tokyo , japan , model-9500 ) ( figure 2 ) was pushed into the muscle block , and the strength of the force was measured and recorded by a computer . four trocars were compared : a new ultrasonic trocar ( usn ) , a conventional trocar ( uso ) that had been inserted 900 times , a 12-mm dilating tip ( dt ) trocar ( ethicon endosurgery , usa ) and a 12-mm versaport ( ve ) trocar ( us surgical co. , tokyo , japan ) . the force required for insertion into the abdominal wall could be varied according to the means of insertion . therefore , we kept in mind the necessity of arranging the times for insertion so as to be the same length , and compared the levels of force among the trocars . it took an average of 6.5 seconds to completely insert the new and conventional us trocars ; the average insertion time was 6.6 seconds for the dt trocar and 6.4 seconds for the ve trocar . the average force was calculated and statistical significance was evaluated with the student t test . an 18-mm incision was made in the skin of a pig , and the us trocar , dilating tip trocar , and versaport trocar were inserted into the abdominal cavity through the incision . trocars were then removed , and the wound was closed with 2 skin staples . bleeding from under the skin was equally controlled by monopolar electrocautery with all 3 types of trocars . in the actual procedure , 1 vertical full - thickness skin stitch up to the muscle fascia layer was placed 1 cm from the wound line , and the suture was retracted with a digital push - pull gauge . the force at which the wound opened 5 mm was recorded as the break strength . the port site not used in the tensile strength evaluation was saved for pathological examination . the full thickness of the abdominal wall around the port was removed , fixed with formalin , and stained with hematoxylin - eosin ( he ) . the temperature around the port site was measured and recorded with a thermal video system tvs 8000 ( nihon avionics , tokyo , japan ) to detect temperature elevations . statistical analysis was performed with the student t test , and p < 0.05 was considered significant . we compared the force necessary to insert the trocar through swine muscle ( table 1 ) . the new and conventional us trocar insertion forces were significantly less than the forces of the other 2 trocars , but the insertion procedure was performed in almost the same time . the dt and ve trocars required the same level of force . required force at insertion . usn = new us trocar ; uso = conventional us trocar ; dt = dilating tip trocar ; ve = versaport trocar . the respective break forces at 1 and 2 weeks were 2.4  0.7 kg ( n = 4 ) and 4.8  0.3 kg ( n = 4 ) for the us trocar , 1.3  0.2 kg ( n = 4 ) and 5.7  0.6 kg ( n = 3 ) , for the dt trocar ; and 2.9  0.9 kg ( n = 4 ) and 3.9  0.4 kg ( n = 4 ) for the ve trocar ( figure 3 ) . the break forces for the us and ve trocars were higher than that of the dt trocar at 1 week , while that of the dt trocar was highest at 2 weeks . . tensile strength at the us trocar site was greater than at the sites where the other 2 tro - cars were used . degenerative changes caused by burning were found in the muscle tissue when the us trocar was used . no difference was found between the us and dt trocars in the epidermal layer ( figure 4 ) . the width of the scar was greater at the us port site than that at the dt port site . we measured temperature changes produced by the us trocar because the other 2 trocars did not produce friction that generated heat . skin temperature around the port site started to increase after the trocar was inserted , and rose to 78.8c just before the peritoneum was broken . we developed an ultrasonic trocar that does not lose blade edge sharpness , and prevents the problem of bleeding . the insertion force of the new us trocar through the abdominal wall was 34% of the force required by commercially available dt trocars . we examined the force with the conventional us trocar , which had been used 900 times . the conventional us trocar insertion force decreased to only 22% less than that of the new us trocar , maintaining ease of insertion as compared with other trocars . the value of the insertion force for the conventional us trocar was only 42.3% of that of the dt trocar , and 45.8% of that of the ve trocar . the us trocar maintained its capacity even with 900 insertions , and this novel instrument had the added advantage that the heat generated by friction between the ultrasonic vibrating trocar and adjacent tissue induced protein denaturation and thereby decreased bleeding . the force of the us trocar insertion was less than that required by the dt and ve trocars . this meant that the us trocar was inserted through the abdominal wall more easily than either the dt or the ve trocar . when we did not insert the trocar smoothly through the abdominal wall , we pushed the trocar more forcefully than usual . the insertion force through the abdominal wall by the us trocar was less than that required by either the dt or the ve trocar . the us trocar had the advantage of a lower probability of abdominal organ injury when not vibrated , even when an organ was touched , because the edge of the us trocar tip was made nontraumatic in order to decrease injuries . therefore , we speculated that the us trocar might decrease the probability of injuring an abdominal organ , or vessels , or both , and thereby decrease potentially fatal complications . this observation indicated that we had developed a reusable trocar with the advantage of cost - effectiveness . bleeding from the port requiring conversion to open surgery was reported in 10 out of 537 cholecystectomies in the japan society of endoscopic surgery 1998 survey . we have used us tro - cars in clinical practice since 1998 and have performed 35 cholecystectomies , 5 gastrectomies , and 10 colonic resections . we have never encountered bleeding when inserting the us trocar . this advantage may be attributable to the nontraumatic tip of the us trocar , which decreased the likelihood of injuring vessels and may also be ascribed to the ultrasonic vibrating tip dividing tissues and thereby preventing vessels from being torn . the us trocar produced friction that generated heat in adjacent tissues . despite the wider scar generated by the us trocar , as compared to the dt trocar , in he - stained specimens , the tensile strength of port site at 1 week was 2.4 kg , which was no less strong than those of the others . the strength at 2 weeks was 4.8 kg and was almost the same as the 5.7 kg achieved with the dt trocar and was stronger than the 3.9 kg achieved with the ve trocar . these findings confirmed the absence of clinical problems in regard to the tensile strength of the port site with the us trocar . however , this thermal scar might allow surgeons to add a stitch between the fascia split made by the us trocar . the skin burn injury associated with temperature elevation has the potential to delay the healing process . shortening the time of contact between the obturator and tissue could decrease the degree of the burn injury . this was accomplished by making the trocar surface smoother and thinner , which decreased resistance during insertion and allowed the trocar to be inserted quickly . the issue of the burning effect on the peritoneum remains to be resolved , but it is anticipated that resolution will be achieved with a smoother and thinner trocar . we developed a reusable ultrasonic vibrating trocar that could be bloodlessly and smoothly inserted more than 900 times through the abdominal wall .
reusable trocars have the advantage of being more cost - effective than disposable trocars . 
 however , the reusable trocar does lose its sharpness on insertion with repetitive insertion . 
 nonreusable trocars are expensive , but the sharpness of the knife facilitates insertion . 
 nonreusable trocars have a safety shield system designed to decrease abdominal organ injury , though the potential problem of bleeding from the abdominal wall port site has yet to be resolved . 
 we therefore developed a novel ultrasonic vibrating trocar that does not lose its sharpness even with repetitive insertion . 
 this trocar prevents bleeding by means of an ultrasonic cavitation effect . 
 the ultrasonic vibrating trocar has the advantage of ease of insertion , and the force required for new reusable trocar insertion was only 34% of the force required for insertion of commercially available nonreusable trocars . 
 the force required for multiply used conventional reusable ultrasonic vibrating trocar insertion , ie , 900 insertions , was maintained at less than 46% of the force required by the corresponding nonreusable trocars . 
 bleeding from the abdominal wall was prevented by an ultrasonic cavitation effect .