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Surgical intervention in patients with infected necrotizing pancreatitis generally consists of laparotomy and necrosectomy. This is an invasive procedure that is associated with high morbidity and mortality rates. In this report, we present an alternative minimally invasive technique: videoscopic assisted retroperitoneal debridement (VARD). This technique can be considered a hybrid between endoscopic and open retroperitoneal necrosectomy. A detailed technical description is provided and the advantages over various other minimally invasive retroperitoneal techniques are discussed. [ABSTRACT FROM AUTHOR]

Early-onset colorectal cancer has been on the rise in Western populations. Here, we compare patient characteristics between those with early- (<50 years) vs. late-onset (≥50 years) disease in a large multinational cohort of colorectal cancer patients ( n = 2193). We calculated descriptive statistics and assessed associations of clinicodemographic factors with age of onset using mutually-adjusted logistic regression models. Patients were on average 60 years old, with BMI of 29 kg/m 2 , 52% colon cancers, 21% early-onset, and presented with stage II or III (60%) disease. Early-onset patients presented with more advanced disease (stages III-IV: 63% vs. 51%, respectively), and received more neo and adjuvant treatment compared to late-onset patients, after controlling for stage (odds ratio (OR) (95% confidence interval (CI)) = 2.30 (1.82-3.83) and 2.00 (1.43-2.81), respectively). Early-onset rectal cancer patients across all stages more commonly received neoadjuvant treatment, even when not indicated as the standard of care, e.g., during stage I disease. The odds of early-onset disease were higher among never smokers and lower among overweight patients (1.55 (1.21-1.98) and 0.56 (0.41-0.76), respectively). Patients with early-onset colorectal cancer were more likely to be diagnosed with advanced stage disease, to have received systemic treatments regardless of stage at diagnosis, and were less likely to be ever smokers or overweight.

Background: Plasma microRNAs (miRNAs) are promising non-invasive biomarkers for colorectal cancer (CRC) prognosis. However, the published studies to date have yielded conflicting and inconsistent results for specific plasma miRNAs., Methods: We have conducted a study using robust assays to assess a panel of nine miRNAs for CRC prognosis and early detection of recurrence. Plasma samples from 144 patients in a prospective CRC cohort study were collected at diagnosis, 6, 12, and 24 months after diagnosis. miRNAs were assayed by Taqman qRT-PCR to generate miRNA normalised copy numbers., Results: Preoperative high plasma miRNA levels were associated with increased recurrence risk for miR-200b (HR [95% CI]=2.04 [1.00, 4.16], P=0.05), miR-203 (HR=4.2 [1.48, 11.93], P=0.007), miR-29a (HR=2.61 [1.34,5.07], P=0.005), and miR-31 (HR=4.03 [1.76, 9.24], P=0.001). Both plasma miR-31 (AUC: 0.717) and miR-29a (AUC: 0.703) could discriminate recurrence from these patients without recurrence. In addition, high levels of miR-31 during surveillance was associated with a three-fold increased risk of recurrence across all time points. Dynamic postoperative plasma miR-141 and 16 levels correlated with recurrence in the surveillance samples., Conclusions: Pre-operative plasma miR-29a, 200b, 203, and 31 are potential CRC prognosis biomarkers. In addition, dynamic postoperative miR-31, 141 and 16 levels are potential biomarkers for the early detection of recurrence during CRC surveillance.

Patients with the HLA-B*1502 allele have a high risk of serious allergic cutaneous reactions from antiepileptic drugs used in the management of trigeminal neuralgia. Awareness of this uncommon but potentially fatal reaction will help to avoid the use of these drugs in patients from racial groups at high risk., (Copyright © 2010 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.)

Background: The feasibility of video-assisted retroperitoneal debridement (VARD) for infected pancreatic walled-off necrosis is established. We provide prospective data on the safety and efficacy of VARD., Design: Multicenter, prospective, single-arm phase 2 study., Setting: Six academic medical centers., Patients: We evaluated 40 patients with pancreatic necrosis who had infection determined using Gram stain or culture., Interventions: Percutaneous drains were placed at enrollment, and computed tomographic scans were repeated at 10 days. Patients who had more than a 75% reduction in collection size were treated with drains. Other patients were treated with VARD. Crossover to open surgery was performed for technical reasons and/or according to surgeon judgment., Main Outcome Measures: Efficacy (ie, successful VARD treatment without crossover to open surgery or death) and safety (based on mortality and complication rates). Patients received follow-up care for 6 months., Results: We enrolled 40 patients (24 men and 16 women) during a 51-month period. Median age was 53 years (range, 32-82 years). Mean (SD) Acute Physiology and Chronic Health Evaluation II score at enrollment was 8.0 (5.1), and median computed tomography severity index score was 8. Of the 40 patients, 24 (60%) were treated with minimally invasive intervention (drains with or without VARD). Nine patients (23%) did not require surgery (drains only). For 31 surgical patients, VARD was possible in 60% of patients. Most patients (81%) required 1 operation. In-hospital 30-day mortality was 2.5% (intent-to-treat). Bleeding complications occurred in 7.5% of patients; enteric fistulas occurred in 17.5%., Conclusions: This prospective cohort study supports the safety and efficacy of VARD for infected pancreatic walled-off necrosis. Of the patients, 85% were eligible for a minimally invasive approach. We were able to use VARD in 60% of surgical patients. The low mortality and complication rates compare favorably with open debridement. An unexpected finding was that a reduction in collection size of 75% according to the results of computed tomographic scans at 10 to 14 days predicted the success of percutaneous drainage alone.

Accurate knowledge of biomechanical characteristics of tissues is essential for developing realistic computer-based surgical simulators incorporating haptic feedback, as well as for the design of surgical robots and tools. As simulation technologies continue to be capable of modeling more complex behavior, an in vivo tissue property database is needed. Most past and current biomechanical research is focused on soft and hard anatomical structures that are subject to physiological loading, testing the organs in situ. Internal organs are different in that respect since they are not subject to extensive loads as part of their regular physiological function. However, during surgery, a different set of loading conditions are imposed on these organs as a result of the interaction with the surgical tools. Following previous research studying the kinematics and dynamics of tool/tissue interaction in real surgical procedures, the focus of the current study was to obtain the structural biomechanical properties (engineering stress-strain and stress relaxation) of seven abdominal organs, including bladder, gallbladder, large and small intestines, liver, spleen, and stomach, using a porcine animal model. The organs were tested in vivo, in situ, and ex corpus (the latter two conditions being postmortem) under cyclical and step strain compressions using a motorized endoscopic grasper and a universal-testing machine. The tissues were tested with the same loading conditions commonly applied by surgeons during minimally invasive surgical procedures. Phenomenological models were developed for the various organs, testing conditions, and experimental devices. A property database-unique to the literature-has been created that contains the average elastic and relaxation model parameters measured for these tissues in vivo and postmortem. The results quantitatively indicate the significant differences between tissue properties measured in vivo and postmortem. A quantitative understanding of how the unconditioned tissue properties and model parameters are influenced by time postmortem and loading condition has been obtained. The results provide the material property foundations for developing science-based haptic surgical simulators, as well as surgical tools for manual and robotic systems.

Surgical simulators are excellent training tools for minimally invasive procedures but are currently lacking in realistic tissue rendering and tissue responses to manipulation. Accurate color representation of tissues may add realism to simulators and provide medically relevant information. The goal of this study was to determine feasible methods for measuring color of in vivo tissue, specifically liver, in a standardized color space. Several compressions were applied to in vivo porcine liver. Three methods were then used to determine the CIELab and/or sRGB colors of normal and damaged liver. Results suggest that there are significant differences between normal and damaged liver color.

With the development of new technologies in surgery, minimally invasive surgery (MIS) has drastically improved the way conventional medical procedures are performed. However, a new learning curve has resulted requiring an expertise in integrating visual information with the kinematics and dynamics of the surgical tools. The Red DRAGON is a multi-modal simulator for teaching and training MIS procedures allowing one to use it with several modalities including: simulator (physical objects and virtual objects) and an animal model. The Red DRAGON system is based on a serial spherical mechanism in which all the rotation axes intersect at a single point (remote center) allowing the endoscopic tools to pivot around the MIS port. The system includes two mechanisms that incorporate two interchangeable MIS tools. Sensors are incorporated into the mechanism and the tools measure the positions and orientations of the surgical tools as well as forces and torques applied on the tools by the surgeon. The design is based on a mechanism optimization to maximize the manipulability of the mechanism in the MIS workspace. As part of a preliminary experimental protocol, five expert level surgeons performed three laparoscopic tasks--a subset of the Fundamental Laparoscopic Skill (FLS) set as a baseline for skill assessment protocols. The results provide an insight into the kinematics and dynamics of the endoscopic tools, as the underlying measures for objectively assessing MIS skills.

As the field of surgical robotics continues to evolve, it is important to keep patient safety in mind. This paper describes a safety control architecture aimed at moving an experimental system in the direction of intrinsically safe operation. The system includes safety features such as: a small number of states, Programmable Logic Controller (PLC) state transition control, active enable, brakes, E-STOP, and a surgeon foot pedal.

We hypothesized that the use of muscle flaps, known as tissue transfer (TT), at the time of abdominoperineal resection (APR) reduces perineal wound complications. A restrospective review of patients undergoing an APR at the University of Washington (1984-2003) was conducted. Perineal wound complications and eventual wound healing were compared in patients with and without TT. Ninety-two patients (mean age, 56.6 years) underwent APR; 23.9 per cent (n = 22) had concurrent TT. Patients undergoing TT were more likely to have cancer (91% vs. 77%, P = 0.05) and radiation therapy (86% vs. 52%, P < 0.01). Operative times were nearly 2 hours longer in patients having TT (7.4 hours +/- 2.5 hours vs. 5.6 hours +/- 1.8 hours, P = 0.03), but lengths of stay were similar (13 +/- 5.9 days vs. 12 +/- 7.6 days, P = 0.5). Patients undergoing TT had a higher rate of all wound-healing complications (59% vs. 40%, P = 0.1) and major wound-healing complications (32% vs. 26%, P = 0.6). However, these differences were not statistically significant. No differences in major complications were identified in patients with and without preoperative radiation therapy (26% vs. 28%, P = 0.8). Fifteen per cent (n = 14) of all patients failed to heal wounds at 6 months, but only 9 per cent (n = 2) of patients undergoing TT failed to heal their wounds at 6 months compared with 17 per cent (n = 12) in the non-TT group (P = 0.3). After controlling for important covariates, patients undergoing TT during an APR did not have a significantly lower rate of wound complications. The impact of TT on wound healing in patients with recurrent cancer and preoperative radiation therapy is suggestive of a benefit but requires prospective investigation.

Recent advances in technology have led to the fusion of MIS techniques and robot devices. However, current systems are large and cumbersome. Optimizing the surgical robot mechanism will eventually lead to its integration into the operating room (OR) of the future becoming the extended presence of the surgeon and nurses in a room occupied by the patient alone. By optimizing a spherical mechanism using data collected in-vivo during MIS procedures, this study is focused on a bottom-up approach to developing a new class of surgical robotic arms while maximizing their performance and minimizing their size. The spherical mechanism is a rotational manipulator with all axes intersecting at the center of the sphere. Locating the rotation center of the mechanism at the MIS port makes this class of mechanism a suitable candidate for the first two links of a surgical robot for MIS. The required dexterous workspace (DWS) is defined as the region in which 95% of the tool motions are contained based on in-vivo measurements. The extended dexterous workspace (EDWS) is defined as the entire abdominal cavity reachable by a MIS instruments. The DWS is defined by a right circular cone with a vertex angle of 60 degrees and the EDWS is defined by a cone with an elliptical cross section created by two orthogonal vertex angles of 60 degrees and 90 degrees. A compound function based on the mechanism's isotropy and the mechanism stiffness was considered as the performance metric cost function. Optimization across both the DWS and the EDWS lead to a serial mechanism configuration with link length angles of 74 degrees and 60 degrees for a serial configuration. This mechanism configuration maximized the kinematic performance in the DWS while keeping the EDWS as its reachable workspace. Surgeons, using a mockup of two mechanisms in a MIS setup, validated these results experimentally. From these experiments the serial configuration was deemed most applicable for MIS robotic applications compared to a parallel mechanism configuration. The mechanical design of a cable actuated surgical robot was based on optimized link length angles. The system is currently being integrated into a fully operated two-arm system. Small form-factor surgical robotic arms with optimized dexterous workspaces will facilitate the integration of multiple arms while avoiding self-collision in the OR of the future.

Effective airway management during laparoscopic anesthesia is important to minimize the adverse consequences of the carbon dioxide (CO2) pneumoperitoneum (PP). During PP, reduced respiratory excursion and tidal volumes with increased CO2 absorption may lead to hypoxia, hypercapnia, and respiratory acidosis. Although these problems can usually be avoided by use of positive pressure ventilation and an endotracheal tube, patients with a restricted airway who cannot be intubated pose a unique challenge. High-frequency jet ventilation (HFJV) has been described as an alternative to endotracheal intubation in other settings. The use of the small-diameter jet tube allows relatively unobstructed access to the larynx during laryngeal surgery. In patients with glottic impairment related to vocal fold immobility, jet ventilation allows positive pressure ventilation without the use of an endotracheal tube or tracheostomy in cases where lung and diaphragmatic compliance permit adequate excursion for ventilation and glottal diameter permits an adequate outflow of air. In this report, we describe the successful use of HFJV combined with an abdominal lifting technique and low-pressure PP for laparoscopic surgery in a patient with glottic compromise related to vocal fold immobility. Using these techniques, a laparoscopic cholecystectomy was performed successfully without endotracheal intubation or the need for a tracheostomy.

The analogy between Minimally Invasive Surgery (MIS) and the human language inspires the decomposition of a surgical task into its primary elements. The frequency of different elements or words" and their sequential associations or "grammar" both hold critical information about the process and outcome of the procedure. Modeling these sequential element expressions using a multi finite states model (Markov model) reveals the grammatical structure of the surgical task and is utilized as one of the key steps in objectively assessing surgical performance. The experimental protocol included 30 surgeons at different levels of training (5xR1,R2,R3,R4,R5, and experts) performing Laparoscopic suturing on an animal model (pig). The kinematics and dynamics of left and right endoscopic tools along with the visual view of the surgical scene were acquired by the Blue DRAGON system. The methodology of decomposing the surgical task is based on a fully connected, finite-states (30 states) Markov model (MM) where the left and right hands are represented by 15 states each. In addition to the MM objective analysis, a scoring protocol was used by an expert surgeon to subjectively assess the subjects' technical performance. An objective learning curve was defined based on measuring quantitative statistical distance (similarity) between MM of experts and MM of residents at different levels of training. The objective learning curve (e.g. statistical distance between MM) was similar to that of the subjective performance analysis. The MM proved to be a powerful and compact mathematical model for decomposing a complex task such as laparoscopic suturing. Systems like surgical robots or virtual reality simulators that inherently measure the kinematics and dynamics of the surgical tool may benefit from inclusion of the proposed methodology for analysis of efficacy and objective evaluation of surgical skills during training.

Minimally invasive surgeiy (MIS) involves a multi-dimensional series of tasks requiring a synthesis between visual information and the kinematics and dynamics of the surgical tools. Analysis of these sources of information is a key step in mastering MIS surgery but may also be used to define objective criteria for characterizing surgical performance. The BIueDRAGON is a new system for acquiring the kinematics and the dynamics of two endoscopic tools along with the visual view of the surgical scene. It includes two four-bar mechanisms equipped with position and force torque sensors for measuring the positions and the orientations (P/O) of two endoscopic tools along with the forces and torques applied by the surgeons hands. The methodology of decomposing the surgical task is based on a fully connected, finite-states (28 states) Markov model where each states corresponded to a fundamental tool/tissue interaction based on the tool kinematics and associated with unique F/T signatures. The experimental protocol included seven MIS tasks performed on an animal model (pig) by 30 surgeons at different levels of their residency training. Preliminary analysis of these data showed that major differences between residents at different skill levels were: (i) the types of tool/tissue interactions being used, (ii) the transitions between tool/tissue interactions being applied by each hand, (iii) time spent while perfonning each tool/tissue interaction, (iv) the overall completion time, and (v) the variable F/T magnitudes being applied by the subjects through the endoscopic tools. Systems like surgical robots or virtual reality simulators that inherently measure the kinematics and the dynamics of the surgical tool may benefit from inclusion of the proposed methodology for analysis of efficacy and objective evaluation of surgical skills during training.

Accurate biomechanical characteristics of tissues are essential for developing realistic virtual reality surgical simulators utilizing haptic devices. Surgical simulation technology has progressed rapidly but without a large database of soft tissue mechanical properties with which to incorporate. The device described here is a computer-controlled, motorized endoscopic grasper capable of applying surgically relevant levels of force to tissue in vivo and measuring the tissue's force-deformation properties.

Objective: Evaluation of the laparoscopic surgical skills of surgical residents is usually a subjective process carried out in the operating room by senior surgeons. The two hypotheses of the current study were: (1) haptic information and tool/tissue interactions (types and transitions) performed in laparoscopic surgery are skill-dependent, and (2) statistical models (Hidden Markov Models--HMMs) incorporating these data are capable of objectively evaluating laparoscopic surgical skills., Materials and Methods: Eight subjects (six residents--two first-year (R1), two third-year (R3), and two fifth-year (R5)--and two expert laparoscopic surgeons) performed laparoscopic cholecystectomy on pigs using an instrumented grasper equipped with force/torque (F/T) sensors at the hand/tool interface, and F/T data was synchronized with video of the operative maneuvers. Fourteen types of tool/tissue (T/T) interactions, each associated with unique F/T signatures, were defined from frame-by-frame video analysis. HMMs for each subject and step of the operation were compared to evaluate the statistical distance between expert surgeons and residents with different skill levels., Results: The statistical distances between HMMs representing expert surgeons and residents were significantly different (alpha < 0.05). Major differences occurred in: (1) F/T magnitudes; (2) type of T/T interactions and transitions between them; and (3) time intervals for each T/T interaction and overall completion time. The greatest difference in performance was between R1 (junior trainee) and R3 (midlevel trainee). Smaller changes were seen as expertise increased beyond the R3 level., Conclusion: HMMs incorporating haptic and visual information provide an objective tool for evaluating surgical skills. Objective evidence for a "learning curve" suggests that surgical residents acquire a major portion of their laparoscopic skill between year 1 and year 3 of training.

Background: Common bile duct (CBD) injury is a serious complication of laparoscopic cholecystectomy (LC). Predictors of this adverse outcome have not been well documented., Hypothesis: Surgeon experience and the use of intraoperative cholangiography (IOC) are associated with a decreased rate of major CBD injury during LC., Design: A retrospective population-based cohort study., Setting: Washington State hospital discharge database reports from 1991 through 1998., Patients: Discharge reports were searched for International Classification of Diseases, Ninth Revision, procedure codes consistent with LC and then evaluated for procedure codes for CBD repair and reconstruction within 90 days of LC., Main Outcome Measure: The rate of CBD injury in patients undergoing LC based on the surgeon's experience and IOC use., Results: In all, 30 630 LCs and 76 major CBD injuries (2.5/1000 operations) were identified in this analysis. There were no significant differences between injured and noninjured patients in demographics, disease, payer status, or hospital variables. A CBD injury occurred in 3.2 of 1000 LCs in the early case order of surgeons compared with 1.7 per 1000 at later points (P = .01) (relative risk, 1.81; 95% confidence interval, 1.44-2.88). The rate of injury in LCs performed without IOC was 3.3 per 1000 compared with 2.0 per 1000 in LCs with IOC (P = .02) (relative risk, 1.7; 95% confidence interval, 1.1-2.6). Surgeon's experience and IOC use were independent predictors of injury., Conclusions: The rate of CBD injury is significantly lower when IOC is used. This effect is magnified during the early experience of surgeons. Systematic use of IOC may significantly reduce the rate of CBD injury.

Background: Percutaneous drainage has been shown to be an acceptable method for treating both pancreatic abscesses and infected pancreatic necrosis. However, percutaneous techniques have certain shortcomings, including the time and labor required and failure of the catheters to adequately drain the particulate debris. Growing experience around the world indicates that there is a role for retroperitoneal laparoscopy as a means of facilitating the percutaneous drainage of infected pancreatic fluid collections and avoiding a laparotomy. Our technique is discussed in this paper., Methods: Once infection is documented in a pancreatic fluid collection by fine-needle aspiration, one or more percutaneous drains are placed into the fluid collection(s). A computed tomography (CT) scan is repeated. If further drainage is indicated, retroperitoneoscopic debridement is performed. Using a combination of the percutaneous drain(s) and the post-drain CT scan, ports are placed and retroperitoneoscopic debridement of the necrosectum is performed under direct visualization. Prior to completion of the operation, a postoperative lavage system is created., Results: Six patients with infected pancreatic necrosis have been treated with this technique. Prior to commencement of our laparoscopic protocol, all six patients would have required open necrosectomy. Four of the six patients were managed with retroperitoneoscopic debridement and catheter drainage alone. Complications included a colocutaneous fistula and a small flank hernia. There were no bleeding complications and no deaths., Conclusion: Although open necrosectomy remains the standard of care for the treatment of infected pancreatic necrosis and pancreatic abscess, there is growing evidence that laparoscopic retroperitoneal debridement is feasible.

Background: Percutaneous drainage of infected pancreatic fluid collections is often unsuccessful. Alternatively, open necrosectomy techniques are very morbid. We hypothesized that in selected cases, laparoscopic techniques could be used to facilitate percutaneous drainage of the residual particulate necrosectum and avoid a laparotomy. We report our experience with laparoscopic assisted retroperitoneal debridement as an adjunct to percutaneous drainage for patients with infected pancreatic necrosis., Methods: Case studies were reviewed retrospectively. We analyzed the course of six patients undergoing laparoscopic assisted debridement of infected pancreatic necrosis after failure of percutaneous drainage. With the drains and computed tomography (CT) scan used as a guide, laparoscopic debridement of the necrosectum was performed., Results: Between November 1995 and December 1999, six patients were treated with this method. In four patients, laparoscopic assisted percutaneous drainage was successful. Two patients required open laparotomy. Complications included a self-limited enterocutaneous fistula and a small flank hernia. No deaths occurred., Conclusions: This early, limited experience has demonstrated the feasibility of laparoscopic assisted percutaneous drainage for infected pancreatic necrosis. With this technique, two-thirds of our patients avoided the morbidity of a laparotomy.

The best method of training for laparoscopic surgical skills is controversial. Some advocate observation in the operating room, while others promote animal and simulated models or a combination of surgery-related tasks. A crucial process in surgical education is to evaluate the level of surgical skills. For laparoscopic surgery, skill evaluation is traditionally performed subjectively by experts grading a video of a procedure performed by a student. By its nature, this process uses fuzzy criteria. The objective of the current study was to develop and assess a skill scale using Markov models (MMs). Ten surgeons [five novice surgeons (NS); five expert surgeons (ES)] performed a cholecystectomy and Nissen fundoplication in a porcine model. An instrumented laparoscopic grasper equipped with a three-axis force/torque (F/T) sensor was used to measure the forces/torques at the hand/tool interface synchronized with a video of the tool operative maneuvers. A synthesis of frame-by-frame video analysis and a vector quantization algorithm, allowed to define F/T signatures associated with 14 different types of tool/tissue interactions. The magnitude of F/T applied by NS and ES were significantly different (p < 0.05) and varied based on the task being performed. High F/T magnitudes were applied by NS compared with ES while performing tissue manipulation and vise versa in tasks involved tissue dissection. From each step of the surgical procedures, two MMs were developed representing the performance of three surgeons out of the five in the ES and NS groups. The data obtained by the remaining two surgeons in each group were used for evaluating the performance scale. The final result was a surgical performance index which represented a ratio of statistical similarity between the examined surgeon's MM and the MM of NS and ES. The difference between the performance index value, for a surgeon under study, and the NS/ES boundary, indicated the level of expertise in the surgeon's own group. Using this index, 87.5% of the surgical procedures were correctly classified into the NS and ES groups. The 12.5% of the procedures that were misclassified were performed by the ES and classified as NS. However in these cases the performance index values were very close to the NS/ES boundary. Preliminary data suggest that a performance index based on MM and F/T signatures provides an objective means of distinguishing NS from ES. In addition, this methodology can be further applied to evaluate haptic virtual reality surgical simulators for improving realism in surgical education.

Endoscopic haptic surgical devices have shown promise in addressing the loss of tactile sensation associated with minimally invasive surgery. However, these devices must be capable of generating forces and torques similar to those applied on the tissue with a standard endoscopic tool. Geared motors are a possible solution for actuation; however, they possess mechanical characteristics that could potentially interfere with tactile perception of tissue qualities. The aim of the current research was to determine how the characteristics of a geared motor suitable for a haptic surgical device affect a user's perception of stiffness. The experiment involved six blindfolded subjects who were asked to discriminate the stiffness of six distinct silicone rubber samples whose mechanical properties are similar to those of soft tissue. Using a novel testing device whose dimensions approximated those of an endoscopic grasper, each subject palpated 30 permutations of sample pairs for each of three types of mechanical loads; the motor (friction and inertia), a flywheel (with the same inertia as motor), and a control (no significant mechanical interference). One factor ANOVA of the error scores and palpation time showed that no significant difference existed among error scores, but mean palpation time for the control was significantly less than for the other two methods. These results indicated that the mechanical characteristics of a geared motor chosen for application in a haptic surgical device did not interfere with the subjects' perception of the silicone samples' stiffness, but these characteristics may significantly affect the energy expenditure and time required for tissue palpation. Therefore, before geared motors can be considered for use in haptic surgical devices, consideration should be given to factors such as palpation speed and fatigue.